# Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and Polar Vortices With VLT/VISIR

Deborah Bardet, Padraig T. Donnelly, Leigh N. Fletcher, Arrate Antuñano, Michael T. Roman, James A. Sinclair, Glenn S. Orton, Chihiro Tao, John H. Rogers, Henrik Melin, et al.

<figure><img src="image_1.png" /></figure>

► To cite this version:

Deborah Bardet, Padraig T. Donnelly, Leigh N. Fletcher, Arrate Antuñano, Michael T. Roman, et al. Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and Polar Vortices With VLT/VISIR. Journal of Geophysical Research. Planets, 2024, 129, 10.1029/2023JE007902. insu-04729906

HAL Id: insu-04729906

https://insu.hal.science/insu-04729906v1

Submitted on 10 Oct 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
JGR Planets

RESEARCH ARTICLE

10.1029/2023JE007902

**Special Section:**

The Frontiers in Jupiter Science
and Exploration

**Key Points:**

* Jupiter's belt/zone thermal structure extends from the equator to the edge of the polar vortices and correlates with the zonal jets

* The cold polar vortices coincides with reflective aerosols, suggesting dynamical entrainment by the northernmost and southernmost jets

* Temporal evolution of the southern auroral hotspot shows a stratospheric cooling after a solar wind compression event

**Supporting Information:**

Supporting Information may be found in
the online version of this article.

**Correspondence to:**

D. Bardet,
db528@leicester.ac.uk

**Citation:**

Bardet, D., Donnelly, P. T., Fletcher, L. N., Antuñano, A., Roman, M. T., Sinclair, J. A., et al. (2024). Investigating thermal contrasts between Jupiter's belts, zones, and polar vortices with VLT/VISIR. *Journal of Geophysical Research: Planets*, 129, e2023JE007902. https://doi.org/10.1029/2023JE007902

Received 17 MAY 2023
Accepted 8 JAN 2024

**Author Contributions:**

**Data curation:** Deborah Bardet, Padraig T. Donnelly, Leigh N. Fletcher, John H. Rogers

**Formal analysis:** Deborah Bardet,
Padraig T. Donnelly, John H. Rogers

**Funding acquisition:** Leigh N. Fletcher

**Investigation:** Deborah Bardet, Padraig T. Donnelly

© 2024. The Authors.

This is an open access article under
the terms of the Creative Commons
Attribution License, which permits use,
distribution and reproduction in any
medium, provided the original work is
properly cited.

<figure><img src="image_3.png" /></figure>

Investigating Thermal Contrasts Between Jupiter's Belts,
Zones, and Polar Vortices With VLT/VISIR

Deborah Bardet¹ ID, Padraig T. Donnelly², Leigh N. Fletcher¹ ID, Arrate Antuñano³ ID,
Michael T. Roman¹ ID, James A. Sinclair⁴ ID, Glenn S. Orton⁴ ID, Chihiro Tao⁵ ID, John H. Rogers⁶,
Henrik Melin¹ ID, and Jake Harkett¹

¹School of Physics and Astronomy, University of Leicester, Leicester, UK, ²Laboratoire de Météorologie Dynamique/Institut Pierre-Simon Laplace (LMD/IPSL), Sorbonne Université, Centre National de la Recherche Scientifique (CNRS), École Polytechnique, Institut Polytechnique de Paris, École Normale Supérieure (ENS), PSL Research University, Paris, France, ³Escuela Ingernieria de Bilbao, Fisica Aplicada, UPV/EHU, Bilbao, Spain, ⁴Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA, ⁵National Institute of Information and Communications Technology (NICT), Tokyo, Japan, ⁶British Astronomical Association, London, UK

**Abstract** Using images at multiple mid-infrared wavelengths, acquired in 2018 May using the Very Large Telescope Imager and Spectrometer (VISIR) instrument on ESO's Very Large Telescope (VLT), we study Jupiter's pole-to-pole thermal, chemical and aerosol structure in the troposphere and stratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones and warm cloud-free cyclonic belts persists throughout the mid-latitudes, up to the polar boundaries, and evidence a strong correlation with the vertical maximum windshear and the locations of Jupiter's zonal jets. At high latitudes, VISIR images reveal a large region of mid-infrared cooling poleward ~64°N and ~67°S extending from the upper troposphere to the stratosphere, co-located with the reflective aerosols observed by JunoCam, and suggesting that aerosols play a key role in the radiative cooling at the poles. Comparison of zonal-mean thermal properties and high-resolution visible imaging from Juno allows us to study the variability of atmospheric properties as a function of altitude and jet boundaries, particularly in the cold southern polar vortex. However, the southern stratospheric polar vortex is partly masked by a warm mid-infrared signature of the aurora. Co-located with the southern main auroral oval, this warming results from the auroral precipitation and/or joule heating which heat the atmosphere and thus cause a significant stratospheric emission. This high emission results from a large enhancement of both ethane and acetylene in the polar region, reinforcing the evidence of enhanced ion-related chemistry in Jupiter's auroral regions.

**Plain Language Summary** A fundamental inquiry driving NASA's Juno mission was the investigation of the potential changes of Jupiter's famous banded structure below the top most clouds. As NASA's Juno spacecraft lacks instrumentation sensitive to the mid-infrared, we have used the ground-based Very Large Telescope Imager and Spectrometer (VISIR) on ESO's Very Large Telescope (VLT) to support the mission since 2016. The 2018 May data set provides a comprehensive view of Jupiter's pole-to-pole thermal, chemical, and aerosol structure; including the Great Red Spot; and the auroral-related heating in the southern polar stratosphere. We show that the alternating pattern of cool cloudy zones and warm cloud-free belts correlate to the zonal winds locations, extends from the equator to the boundary of the polar vortices (~64°N and ~67°S). Comparing this ground-based data set with Juno observations, we show that the polar regions experience radiative cooling from the upper troposphere to the stratosphere, probably induced by the reflective polar aerosols, and confined at the poles by the polar vortices. However, the southern stratospheric polar vortex is partly masked by a large auroral emission, a signature of an interaction between the magnetosphere and stratosphere of Jupiter, which causes a ~20 K warming as deep as the middle stratosphere. Excess hydrocarbons within the polar domain reinforces the evidence of enhanced ion-related chemistry in Jupiter's auroral regions, resulting from charged particles precipitating from the top of the atmosphere to lower altitudes.

**1. Introduction**

The meridional distribution of chemical trace species in the middle atmosphere of Jupiter provide crucial insights
into the thermal and dynamical processes occurring in this planetary atmosphere. Despite being observed
**Methodology:** Deborah Bardet, Padraig T. Donnelly, Leigh N. Fletcher, Arrate Antuñano, Michael T. Roman, James A. Sinclair, Glenn S. Orton, John H. Rogers, Henrik Melin, Jake Harkett

**Project Administration:** Leigh N. Fletcher

**Resources:** James A. Sinclair, Glenn S. Orton, Chihiro Tao, John H. Rogers, Henrik Melin

**Software:** Leigh N. Fletcher, Arrate Antuñano, Michael T. Roman

**Supervision:** Leigh N. Fletcher

**Validation:** Leigh N. Fletcher, Arrate Antuñano, Michael T. Roman

**Writing – original draft:** Deborah Bardet

**Writing – review & editing:** Deborah Bardet, Padraig T. Donnelly, Leigh N. Fletcher, Arrate Antuñano, Michael T. Roman, James A. Sinclair, Glenn S. Orton, Chihiro Tao, John H. Rogers, Henrik Melin, Jake Harkett

for decades, Jupiter remains enigmatic in terms of its global circulation, eddy-to-mean interaction from the troposphere to the upper atmosphere, chemical processes and the meridional and vertical transport of chemicals.

For instance, the latitudinal distribution of chemical species such as ammonia (Achterberg et al., 2006; de Pater et al., 2016; Gierasch et al., 1986; C. Li et al., 2017), phosphine (Fletcher et al., 2009; Giles et al., 2017; Grassi et al., 2020) and para-hydrogen (Conrath et al., 1998; Fletcher, de Pater, et al., 2017), combined with the observed temperature and aerosol distributions, may suggest that Jupiter's banded appearance of belts and zones is related to meridional circulation patterns associated with each zonal jet, and that the sense of the circulation changes dramatically as a function of height in Jupiter's troposphere (Fletcher et al., 2021). This proposed "stacked-cell" circulation may be comprised of deep Ferrel-like cells below the clouds, dominated by eddy forcing of zonal winds (Duer et al., 2021), and upper cells above the clouds of eddy dissipation and zonal wind decay with altitude (Fletcher, Kaspi, et al., 2020; Ingersoll, 2020; Showman & de Pater, 2005). The vertical shear on the zonal winds may be inferred from the meridional temperature gradients via the thermal wind equation (Holton, 2004), and previous studies have shown that the zonal winds appear to decay with altitude from the cloud top to the tropopause (Conrath et al., 1990; Pirraglia et al., 1981). The dissipation mechanism, and its source, remains unclear and has never been directly observed, but could result from wave or vortex stresses opposing the winds (Orsolini & Leovy, 1993; Pirraglia, 1989).

These meridional circulation cells could explain the differences in temperatures, aerosols, and gaseous composition between the cold, cloudy anticyclonic zones and the warm, comparatively cloud-free cyclonic belts. In the upper troposphere, zones experience adiabatic expansion above the clouds and below the stably stratified tropopause, and are favorable to condensation of ices that enhance aerosol reflectivity; whereas belts experience adiabatic compression, explaining their comparatively cloud-free structure. Moreover, zones are surrounded by eastward-propagating jets at their polar edges, and westward-propagating jets on their equatorward edges. Conversely, the belts exhibit westward jets along their poleward boundaries and eastward jets on their equatorward boundaries. Strong alternating eastward- and westward-propagating zonal jets generate potential vorticity gradients that act as barriers to meridional mixing (Read et al., 2006). Observations from Voyager/IRIS and Cassini/CIRS suggest that this banded pattern of temperature, aerosol and zonal winds persists up to high latitudes near 60° in the upper troposphere (Conrath & Pirraglia, 1983; Flasar & Gierasch, 1986; Fletcher et al., 2016; Simon-Miller et al., 2006), but neither spacecraft provided good coverage of the mid-infrared brightness gradients at Jupiter's high latitudes in the polar domains. To explore Jupiter's polar regions in the mid-infrared, we require the high spatial resolution offered by world-class ground-based observatories with primary mirror diameters of 8 m or larger to mitigate the blurring effects of diffraction.

Jupiter's stratosphere shows signs of equally rich dynamics as its troposphere, with numerous wave signatures in the temperature fields and isolated thermal disturbances in tropical and auroral regions (Fletcher, Orton, et al., 2017; Giles et al., 2023; Sinclair et al., 2017). As with the circulations in the troposphere, stratospheric circulations are mostly deduced from the observation of anomalies in the distribution of trace species, such as hydrocarbons. The main by-products of methane photochemistry, ethane ($C_2H_6$) and acetylene ($C_2H_2$), display surprising differences in their meridional distribution in the middle stratosphere (from 1 to 10 mbar). While acetylene displays a maximum at low latitudes, following the yearly averaged insolation as is expected from photochemistry, long-lived ethane increases toward the poles up to the ~70°-boundary (Fletcher et al., 2016; Giles et al., 2021; Melin et al., 2018; Nixon et al., 2007, 2010; Zhang et al., 2013). In the same vein, HCN and $CO_2$, introduced into Jupiter's stratosphere following comet Shoemaker-Levy 9 (SL 9) impact in 1994, follow different migration schemes: HCN has been efficiently mixed from the impact site (44°S) to northern mid-latitudes, while $CO_2$ has been greatly enhanced near the south pole (Cavalié et al., 2017; Griffith et al., 2004; Lellouch et al., 2006; Moreno et al., 2003; Sinclair et al., 2023). Photochemical models, including parameterizations of meridional, vertical diffusion and advection, attempted to address the observed opposite distributions of $C_2H_6$ and $C_2H_2$, or HCN and $CO_2$, but none could satisfactorily reproduce the observations (Hue et al., 2018; Lellouch et al., 2006; Zhang et al., 2013). To date, there is no clear picture of the global dynamical transport and the chemical processes on those chemical species during their journey from the equator toward the polar latitudes.

However, poleward of the ~70° boundary, observations of Jupiter's atmosphere reveal interactions between its magnetosphere and stratosphere, in particular through the polar aurora interaction with the middle atmosphere. Auroral regions at Jupiter's northern and southern poles are prone to injections of high-energy ions and electrons coming from the jovian magnetosphere and solar wind compression events. As they propagate downwards
into the neutral atmosphere, those high-energy charged particles deposit their energy down to approximately 1 mbar (Flasar et al., 2004), resulting in a magnetosphere-to-stratosphere warming (caused by the charged particle precipitation, ion drag and Joule heating). Moreover, the increased electron flux in auroral regions also leads to increased rates of ion-neutral reactions and electron recombination, thus altering the chemistry in auroral regions compared to non-auroral regions and lower latitudes (Sinclair et al., 2017, 2018; Sinclair, Moses, et al., 2019). The increased flux of electrons in the auroral regions is sensed in both the mid-infrared emission and ultra-violet absorption: (a) by modifying the thermal and chemical structure of the atmosphere, there is an enhancement of the mid-infrared emission chemical species in the stratosphere, such as methane ($CH_4$), acetylene ($C_2H_2$), ethylene ($C_2H_4$) and ethane ($C_2H_6$); (b) the modification of the chemical structure can result in an increase in abundance, that acts to enhance the absorption in the ultra-violet (Caldwell et al., 1980, 1983; Drossart et al., 1993; Kim et al., 1985; Kostiuk et al., 1993; Livengood et al., 1993; Sinclair et al., 2017, 2018; Sinclair, Moses, et al., 2019).

Despite mid-infrared observations over several decades, the interaction between auroral particle penetration and the vertical and horizontal chemistry in the deeper layers of the neutral atmosphere remain poorly understood. Indeed, as auroral processes are the result of charged particles precipitating from the top of the atmosphere to higher pressures, any effect of the aurora in the lower layers is expected to be a continuous top-down effect. Sinclair et al. (2017) detected two discrete vertical levels of heating. On one hand, they found heating at 10 µbar, corresponding to the lower boundary of Jupiter's thermosphere during an auroral event, plausibly due by chemical heating, $H_2$ dissociation from excited states and Joule heating from Pedersen currents (Badman et al., 2015; Grodent et al., 2001; Yates et al., 2014). On the other hand, they also found a deeper layer of heating at 1 mbar, which could be due to adiabatic heating by subsidence in the auroral hotspot regions (Sinclair et al., 2017), whose horizontal diffusion would be confined to the pole by an asymmetric auroral jet surrounding the main auroral oval. In fact, ground-based observations of stratospheric polar HCN and CO highlighted strong westward and eastward jets at 0.1 mbar, respectively located at 70°S and 55°N, delimiting the main auroral emission boundaries (Rego et al., 1999), enclosing within the main auroral oval the subsidence heating from the sub-µbar levels (Chaufray et al., 2011) toward the middle stratosphere (Cavalié et al., 2021) through adiabatic compression. Such auroral jets could act as a guide to confine aurora-heated, hydrocarbon-enriched gas to the pole during the entire advection of the gas to deeper pressures, before being diffused or transported toward other latitudinal and/or longitudinal regions outside of the main auroral oval. Moreover, the polar $C_2H_2$ (from the auroral ion-neutral chemistry) is suspected to be transported outside the auroral oval, toward quiescent polar regions and toward equatorward regions, where the neutral chemistry dominates and where acetylene may be quickly converted into ethane (Giles et al., 2023; Sinclair et al., 2017). This hypothetical transport and transformation of acetylene into ethane out of the auroral main oval might explain the homogenization of $C_2H_6$ across the entire region (Sinclair et al., 2017), as well as the poleward enhancement of ethane observed from space and ground-based facilities (Fletcher et al., 2016; Melin et al., 2018; Nixon et al., 2007) that remains unexplained by neutral photochemical models (Hue et al., 2018).

This paper presents new measurements of the spatial variability of temperature, aerosols, and gaseous species associated with Jupiter's banded structure, polar vortex boundary, auroral heating, and large-scale features like the Great Red Spot (GRS). We use a global mid-infrared map of Jupiter acquired by the VISIR instrument (Very Large Telescope (VLT) Imager and Spectrometer for InfraRed) on ESO's VLT in May 2018. The high spatial resolution afforded by VLT allows us to measure infrared contrasts at Jupiter's mid-latitudes and polar vortices that were inaccessible to flyby spacecraft (Voyager and Cassini), and beyond the reach of observations from 3-m diameter facilities like the IRTF (Fletcher et al., 2016) due to more severe diffraction of the beam. The May-2018 global map was the most complete (in terms of spatial and spectral coverage) data set acquired as part of a 2016–2022 program of support for NASA's Juno spacecraft. This data set was obtained simultaneously with Juno's 13th perijove (closest approach), and provides an unprecedented view of Jupiter's poles in the mid-infrared, allowing us to compare simultaneous Juno observations to the mid-infrared maps.

The data set and the reduction and calibration methods are presented in Section 2. Different methods of spectral retrieval are explored in Section 3. We describe the retrieval results, with a focus on the belt/zone thermal structure and chemical species distribution, and their implication on the jovian atmospheric dynamics in Section 4. Section 5 provides insights about the thermal and cloud structures of the GRS. The polar cloud distribution, with comparison to Juno observations on Perijove 13, will be provided in Section 6, and the time variation of the auroral-related thermal signature in the stratosphere will be inferred in Section 7. Finally, we will draw conclusions and perspectives in Section 8.
## 2. Observations and Processing Method

### 2.1. VLT/VISIR 24–27 May 2018 Data Set

As NASA's Juno spacecraft lacks instrumentation sensitive to the mid-infrared (7–25 µm), a program of ground-based infrared support has been underway since 2016 (i.e., Antuñano et al., 2020, 2021; Fletcher, Orton, et al., 2017; Fletcher, Orton, et al., 2018; Fletcher, Melin, et al., 2018; Fletcher, Orton, et al., 2020). To this purpose, we use the VLT Imager and Spectrometer for the mid-infrared (VISIR, Lagage et al., 2004) on the “unit telescope” UT3 Melipal. The array of VISIR is 1,024 × 1,024 pixels, with a pixel scale of 0.045” providing a field of view of 38 × 38”. The maximum chop throw of 25” combined with the maximum angular size of Jupiter of ~44” requires independent observations to acquire the northern and southern hemisphere, sometimes spread over several nights. To observe an entire hemisphere in all wavelengths, it is necessary to observe multiple images in a sequential way, in a block of approximately 50 min that is then repeated as Jupiter rotates. The instrument provides diffraction-limited filtered imaging at high sensitivity in the M band (at 4.82 µm), N band (8–13 µm), and Q band (16–25 µm) of the mid-IR, chopping and nodding to remove the sky background. It also features a long-slit spectrometer that performs N-band spectroscopy with spectral resolutions varying between 150 and 30,000 (not used in this study).

Images at multiple wavelengths between 4.9 and 19.5 µm have been analyzed to study the thermal, chemical, and aerosol structure of Jupiter's belts, zones, and polar domains. In particular, a “visitor mode” observing run in 2018 May (coinciding with Juno's perijove 13) provided global coverage of Jupiter in eleven narrow-band filters (Figure 1). This data set is composed of 281 observations, taken on the 24 May 2018 (02:29–07:45 UT), 24–25 May 2018 (23:02–04:43 UT), 25–26 May 2018 (23:06–08:01 UT), and 26–27 May 2018 (22:46–04:41 UT). This 11-mid-infrared-filter set mainly senses the stratospheric temperature through the methane (CH₄) band emission (7.9 µm), tropospheric temperature via the collision-induced hydrogen-helium continuum (13.04, 17.65, 18.72, 19.50 µm), temperature and aerosol opacity deeper in the troposphere (8.59 and 8.99 µm), tropospheric distribution of ammonia gas and temperature via NH₃ absorption bands (8.59, 8.99, 9.82, 10.49, 10.77, and 12.27 µm), acetylene (C₂H₂, 13.04 µm) and ethane (C₂H₆, 12.27 µm). The latter two wavelengths are particularly interesting in the polar regions, as the contribution of the hydrocarbon emissions become as strong or stronger than the contribution from the continuum emissions. Thus, those two filters are more sensitive to the hydrocarbon distribution at high emission angles than at low emission angle, implying a higher sensitivity to the hydrocarbons in the polar regions than at the equator. In addition, there are two other filters that sense the NH₃ and temperature at 11.25 and 11.88 µm; but these wavelengths were only used once to image the southern hemisphere, so are not included in our global analysis. For this data set, Jupiter's atmosphere is covered from 89°S to 87°N (in planetocentric latitude), and describes a sub-observer of –3.76° (offering a better view of the southern pole). To determine the maximum latitude up to which we trust the observations, we use the diffraction limit, defined as 1.22λ/D, where λ is the considered wavelength and D the mirror diameter of the telescope. For the longest wavelength of this data set (19.5 µm), the diffraction limit is ~0.6 arcsec. For simplicity, we consider Jupiter as a sphere with an angular radius at the observational time of 22.2 arcsec. In the case of optimal condition of observation, the farthest north we can point the telescope and keep the beam fully on Jupiter is half the diffraction limit at 19.5 µm (i.e., 0.3 arcsec). Hence, we estimate that within a disk of 0.3 arcsec for the longest wavelength of the data set, the maximum latitude is ~80° (i.e., $\text{lat}_{\text{max}} = \arcsin(\frac{22.2-0.3}{22.2})$), for a perfect sphere and a sub-observer latitude of 0°. Hence, for any measurements within 10° plus the sub-observer latitude from either pole at 19.5 µm, the planetary flux would be convolved with the much colder deep sky flux. Therefore, poleward of 83°S and 77°N, Jupiter's thermal flux can be considered as contaminated for the purposes of the thermal retrieval. In the following sections, we are not taking into account the data poleward of those two latitude thresholds. We also note that hereafter all latitudes will be expressed in planetocentric form.

The 11 global maps obtained after image processing and correction (explained in Section 2.2) permit an overview of some of Jupiter's famous features, which will be detailed in the present study, such as the banded structure of cool zones and warm belts, and large vortices such as the GRS and Oval BA. Jupiter's equatorial stratospheric oscillation (sometimes called the Quasi-Quadrennial Oscillation “QQO,” Leovy et al., 1991) was in a phase with a warm equatorial band at 7.9 µm in 2018.

Several bright spots are depicted in these global maps. For instance, the bright spot seen in the 60°W region of the Southern Equatorial Belt (SEB) in the 10.77-, 10.49-, 9.82-, 8.99-, and slightly in the 8.59-µm filters,
<figure><img src="image_4.png" /><figcaption>**Figure 1.** Global maps for the Very Large Telescope/Very Large Telescope Imager and Spectrometer N-Band (7.9–13.04 µm) and Q-Band (19.50, 18.72, and 17.65 µm) filters between 24 and 27 May 2018, obtained by combining the individual calibrated cylindrical maps. Maps shown here have been also corrected to remove the limb-darkening or limb-brightening effect (see Section 2.3). Gaps near 240°W are due to missing data.</figcaption></figure>

which seems correlated with one of the SEB Barges labeled in the ground-based amateur observations map (Figure 2). These cyclonic barges are bright in the mid-infrared and dark in the visible due to some combination of warmer temperature, aerosol clearing, and depleted NH₃. In the stratosphere and at the tropopause level (i.e., at 7.9-, 17.65-, 18.72-µm on Figures 1a–1c, respectively), there is an intense bright spot located at 280°W/25°N, reminiscent of the 14-K-warm anomaly observed from 28–29 May to 5 June 2017 at 178°W/28°N at a pressure of 1.2 mbar, but disappeared from July 2017 to February 2018 (Giles et al., 2020). Giles et al. (2020) showed that this stratospheric anomaly occurred at the same time as a disruption of the QQO, similar to Saturn's equatorial oscillation disturbance by the stratospheric “beacon,” resulting from the Great White Spot in 2010–2011 (Fletcher, Guerlet, et al., 2017). Additional study is needed to confirm whether this 280°W/25°N bright spot observed with VISIR is linked to a new disruption event of the downward propagation of the QQO.
<figure><img src="image_5.png" /><figcaption>**Figure 2.** Ground-based amateur observations during the 23–24 May 2018 night taken by Christopher Go, Johnny Hsieh and Kuknhiko Suzuki, processed and mapped by Marco Vedovato and annotated by John Rogers. Published on the British Astronomical Association, into the “Jupiter in 2018, Report no.5” https://britastro.org/section_information/_jupiter-section-overview/jupiter-in-2017-18/jupiter-in-2018-report-no-5.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Figure 3.** Details of zonal brightness temperature perturbation maps, calculated from the zonally averaged profile of each global map per night and for each filter to highlight the thermal perturbation at high northern latitudes in the stratosphere. Only the first three nights of observations are shown here, because this part of the atmosphere was not observed during the last night.</figcaption></figure>

The 7.9-µm filter reveals significant brightness temperature variability in the northern stratosphere, suggesting large wave activity during Jupiter's northern winter (the season on Jupiter in 2018 May), in contrast with the southern hemisphere showing a more quiescent brightness temperature behavior. In particular, in the 50–60°N

latitude band, there are two warm anomalies (in terms of $T_B$) respectively located at 70 and 230°W System III (Figure 1a), also seen in the 12.27-µm filter sensing $C_2H_6$. By subtracting the zonal-mean brightness temperature, we can see the anomaly clearly in Figure 3 over multiple nights (only the 70°W anomaly is showed on Figure 3). Both of these warm anomalies appear to be located on the eastward edge of a cold anomaly. The persistence of these two repetitive features near 50°N, equidistant from each other, is reminiscent of a planetary-scale Rossby wave, comparable to those circumpolar waves observed around the southern pole (Barrado-Izagirre et al., 2008). Due to the short timescale of the present data set, it is not possible to highlight any preferential direction of propagation and, thus determine if the cold anomaly propagates to equatorward latitudes through time, characteristic of a baroclinic system.

Two other wave patterns are visible around the northern tropical regions of Jupiter, the first one in the tropospheric Northern Equatorial Belt (NEB) centered near the 15°N latitude, and the second one in the stratospheric Northern Tropical Belt (NTB) centered at 20°N, both reminiscent of the two slow-propagating thermal waves observed in 2015/2016 during the NEB expansion with VLT/VISIR (Fletcher, Orton, et al., 2017). Between 10 and 25°N, a pattern of consecutive warm and cold anomalies from 360 to 300°W is observed in all tropospheric filters, extended up to the tropopause, and observed for the four nights of observation (Figures 4a and 4b). In the same
<figure><img src="image_7.png" /><figcaption>**Figure 4.** Details of zonal brightness temperature perturbation maps, calculated from the zonally averaged profile of each global maps per night and for each filter to highlight the thermal perturbation induced by any planetary-scale waves in the Northern Equatorial Belt and the Northern Tropical Belt. Here, only the maps for the (a) 8.59, (b) 10.77, and (c) 7.90 µm filters are shown as they depict the larger signal of the wave-induced thermal perturbation for all nights.</figcaption></figure>

vein, temperature perturbation maps of the stratospheric 7.9 µm-filter depict a feature of consecutive cold and warm anomalies from 360 to 260°W. In both cases, the zonal-mean brightness temperature perturbations maps, focusing on the areas where the waves are most visible, show some time variations in the shape and extension for numerous thermal anomalies, however there is no significant displacement of the patterns toward the east or the west during this 4-day window. These waves appear stationary within the 4 days of the observations, consistent with the slow propagation of NEB and NTB waves observed by Fletcher, Orton, et al. (2017). Hence, the determination of the physical characteristics of these waves, such as the wave speed, direction of propagation, etc., remain unfeasible for the short time series of these data.

Most of the upper-tropospheric filters (i.e., wavelengths larger than 10 µm), as well as the stratospheric 7.9-µm filter, display a well-defined cold polar vortex at each pole (Figure 1), in particular outside of the main auroral oval and/or for filters where the auroral-related emission is not too bright to mask the cold vortex boundaries. For instance, the three Q-band filters (19.50, 18.72, and 17.65 µm) show a significant cooling from ~65° to the pole in both hemispheres. Because of the large mid-infrared emission in the southern auroral oval (360–300°W and 90–0°W System III), the southern polar vortex is not readily visible in the N-band maps. However, the north polar vortex boundary is easily seen in the stratosphere (7.9-µm) and in the acetylene and methane emission band (12.27 and 13.04-µm) as a significant cold area all around the pole, only disturbed by the plausible (but weaker than the southern one) northern auroral-related brighter emission (in the northern aurora oval, from 260° to 150°W System III). A detailed characterization of the polar dynamics, the size of the polar vortices, and the auroral-related heating will be provided in Sections 6 and 7.

## 2.2. VLT/VISIR Data Processing

Reduction of VLT/VISIR observations followed standard techniques for mid-infrared data sets (Fletcher et al., 2009) and are briefly summarized here.

### 2.2.1. Detector Readout Noise

When illuminated by a bright source like Jupiter, VISIR displays vertical and horizontal fixed-pattern noise that must be removed before data analysis. Vertical striping noise is the result of differences in detector readout noise and inhomogeneous illumination by the extended source of Jupiter. The multiplicative nature of detector noise in the thermal infrared leads to a flux-dependent striping pattern which cannot be easily removed by flat-fielding or dark-frame subtraction. Planetary and deep-space pixels are separated by a flux threshold to approximate the location of the limb, and band-pass filtering is performed on each detector half independently to avoid mixing readout noise. A combination of low-pass and high-pass filtering (vertical column-averaging then horizontal Gaussian smoothing) is used to isolate the striping pattern for subtraction from planetary pixels. The central burst of noise is the dominant horizontal component of the fixed pattern noise and is treated analogously to the vertical component. Donnelly (2021) elaborates on this filtering technique and uses quantitative validation metrics to show that, although noise is never perfectly removed, jovian information is optimally preserved.
### 2.2.2. Geometric Registration

The chop-nod subtracted and destriped images have been processed, assigning latitude, longitude, and emission angle values to each location on the disc. To do this, orbital ephemerides of the planet at the time of each observation were used to generate a virtual image of the planetary limb that is manually fitted to the observed limb by eye. The observed radiance was then projected into a stereographic latitude-longitude map ($0.5° × 0.5° resolution$), along with the emission angles, the radial Doppler velocity, and the solar incidence angle for each latitude and longitude. This limb-fitting method has been used for other mid-IR imaging data sets and was estimated to produce errors no larger than $±0.2$ K in brightness temperature and $1.5°$ in latitude (Fletcher et al., 2009).

### 2.2.3. Radiometric Calibration and Uncertainties

Each cylindrical map was initially radiometrically calibrated using the technique outlined in Fletcher et al. (2009). For each VLT/VISIR filter, a central-meridian zonal-mean profile of radiance was extracted for each observation, using a box of 60°-longitude width, centered at the central meridian longitude (in System III, LCMIII) for each map. Hence, we have selected from 6 to 8 individual central meridian profiles per filter, which were averaged together to obtain a pole-to-pole meridian profile of radiance per VLT/VISIR filter. Finally, the averaged pole-to-pole meridian profiles were calibrated to a low-latitude (from 5°S to 5°N for the 7.9 µm filter) or a full averaged meridional profile of radiance from spacecraft data (Figure 5). N-band measurements (7.90–13.04 µm) were scaled to the zonal-mean radiance profile from the Cassini Composite Infrared Spectrometer (CIRS), captured in December 2000–January 2001 from a near-equatorial flyby, minimizing the emission angle effects for the low latitudes (Figures 5a and 5e–5k). However, because the Cassini/CIRS Q-band measurements were not resolved over latitude, the VLT/VISIR Q-band measurements (17.65, 18.72, and 19.5 µm, respectively in Figures 5b–5d) were scaled to the zonal mean radiance from the Voyager InfraRed Interferometer and Spectrometer (IRIS) (Deming et al., 1989, 1997; Orton et al., 1994, 1998; Simon-Miller et al., 2006). The zonally averaged Cassini/CIRS and Voyager/IRIS meridional radiance profiles were convolved with the VLT/VISIR filter functions and the telluric transmission spectrum (calculated with ATRAN, Lord, 1992).

This method of radiometric scaling assumes that the average global temperature of Jupiter has not changed systematically over time, leaving the data set insensitive to changes between the Voyager and Cassini observations, as noted by Orton et al. (1991) and Simon-Miller et al. (2007). A global systematic change in mean temperature could cause a systematic difference in the retrieved temperatures, although Simon-Miller et al. (2006) show the zonal mean structure of Jupiter measured by Voyager/IRIS and Cassini/CIRS and the global mean temperature did not appear to have changed between the data sets (1979–2000). Additionally, a comparison of Voyager data and data from the Stratospheric Observatory for Infrared Astronomy by Fletcher, de Pater, et al. (2017) suggests a thermal change of no larger than 5 K in the Q band over the 35-year period. Nevertheless, the infrared brightness of localized regions of Jupiter is known to vary dramatically - the shifting pattern of the stratospheric oscillation; the fades, revivals, and upheavals of the equatorial belts and zones; and interhemispheric changes that may be related to seasonal variability (e.g., Antuñano et al., 2020; Orton et al., 2022). By scaling the VISIR data to spacecraft observations across all latitudes within ±60° of the equator, our radiometric calibration is insensitive to these localized brightness changes. Antuñano et al. (2020) estimated the error introduced by this scaling to be 0.95 K in the worst case, less than 0.05 K in the best case, and 0.3 K on average. In summary, assuming negligible global temperature changes provides a consistent calibration across this VLT/VISIR data set used hereinafter.

In addition to the systematic uncertainty described above, the measured VLT/VISIR radiances are subject to random uncertainties associated with the electrical and thermal state of the electrons in the VISIR CCDs (dark current), and the inherent variability of the telluric atmosphere. The high quality of the VISIR AQUARIUS sensors means that the majority of the variability in pixel brightness is real, so we can estimate the random noise by the standard deviation of the background sky pixels in each image. This is typically less than 5% of the mean radiance in each image across all filters, so as a conservative estimate we apply a consistent 5% uncertainty to all radiance points in each spectrum. The resulting uncertainty from random noise throughout the N and Q bands is 0.4–0.9 K in brightness temperature (Antuñano et al., 2020, 2021).

## 2.3. Center-To-Limb Corrections

For the purposes of displaying the multiple VISIR observations as a global map, we need to remove the limb darkening (troposphere-sensing filters) or limb brightening (stratosphere-sensing filters) from each observation.
<figure><img src="image_8.png" /><figcaption>**Figure 5.** Calibrated central-meridian radiances (orange) for the Very Large Telescope (VLT)/Very Large Telescope Imager and Spectrometer (VISIR) N-Band (7.9–13.04 µm) and Q-Band (19.50, 18.72, and 17.65 µm) filters using Cassini/CIRS and Voyager/IRIS meridional profiles (green), respectively. Individual central meridian measurements are shown as black dots. The calibration coefficient of the pole-to-pole radiance profiles (defined as the fraction between the mean value of the radiance profile observed by VLT/VISIR and the mean value of the radiance profile observed by Cassini/CIRS or Voyager/IRIS) is indicated on the top right of each panel.</figcaption></figure>

For each filter, we calculated an average variation of brightness temperature as a function of the cosine of the emission angle, and corrected each cylindrical map with this adjustment. For the 10 N-Band filters (the stratospheric 7.9 µm and the tropospheric 8.59–13.04 µm filters), we averaged the two tropical latitude bands from the brightness temperature maps, from 5 to 25° of latitude in each hemisphere, and calculated a fourth-order polynomial function of the brightness temperature variation in terms of emission angle (Figures 6a and 6e–6k). For the three Q-Band filters (17.65, 18.72, 19.50 µm), we only used the southern tropical band of brightness. Effectively, several tests using both the northern and the southern tropical band for the Q-Band filters failed in the correction of the center-to-limb darkening effect. The only way to correct these three filters was to remove the NEB in the
<figure><img src="image_9.png" /><figcaption>**Figure 6.** Polynomial adjustment of Very Large Telescope/Very Large Telescope Imager and Spectrometer N-Band (a, e-k) and Q-Band (b-d) to correct the center-to-limb darkening/brightening effects to enable merging of individual observations into a cylindrical map. For each filter, the left panel shows the brightness temperature variations over the selected latitude band (black dots) superimposed with the corresponding fourth order polynomial function (red line); the middle panel shows the variations of the center-to-limb factor correction ($p(1)/p(μ)$) where $μ$ is the cosine of the emission angle); and the right panel show the corrected brightness temperature variations over the selected latitude band, that is, $T_B \times p(1)/p(μ)$. These three fields are shown as a function of the cosine of the emission angle.</figcaption></figure>
sample of data used to calculate the polynomial adjustment (Figures 6b–6d). Hence, we obtained an unique poly-
nomial adjustment function for each VLT/VISIR filter, that was applied to each cylindrical map to correct the
limb effects, and afterward those corrected cylindrical maps were combined to construct the global maps shown
in Figure 1. Of course, as we use an average center-to-limb polynomial adjustment, some maps still remain a
reduced limb-brightening or limb-darkening effect (for instance in the northern polar regions of the 10.77, 10.49,
9.82 or even 8.99-μm filters) that does not prevent us from identifying polar phenomena in the following sections.

3. Retrieval

**3.1. Retrieval Calculation Pipeline**

To derive temperatures, aerosols, and gaseous abundances from the VLT/VISIR 24–27 May 2018 data set, we used the Non-linear optimal Estimator for MultivariatE spectral analySIS (NEMESIS, Irwin et al., 2008) retrieval model, comprised of a radiative transfer code and an inversion algorithm.

NEMESIS uses the radiative transfer equations to forward-model mid-infrared spectra from a reference atmosphere. This reference atmosphere is described by several prior profiles of temperature, aerosols and molecular species from previous observations and modeling studies (Fletcher et al., 2009; Moses et al., 2005; Niemann et al., 1998; Nixon et al., 2007; Romani et al., 1993; Seiff et al., 1998). The reference atmosphere contains vertical distributions of temperature, ammonia ($NH_3$), phosphine ($PH_3$), acetylene ($C_2H_2$) and ethane ($C_2H_6$) from a 30°N-to-30°S meridian average of Cassini/CIRS results, gridded from 10 bar to 1 µbar on 120 vertical levels (Fletcher et al., 2009; Nixon et al., 2007). The temperature profile derived from Cassini/CIRS originally used the *T(p)* from the Galileo probe Atmospheric Structure Instrument (ASI, Seiff et al., 1998) as prior. Diacetylene ($C_4H_2$) and ethylene ($C_2H_4$) prior profiles are included based on the results from the photochemical model of Romani (1996). The methane ($CH_4$) prior profile results from the photochemical model calculations of Romani et al. (1993), reflecting the atmosphere based on the descent of the Galileo Probe (Seiff et al., 1998), with some adjustments: the deep $CH_4$ abundance has been enhanced by 5%, to match the results of the Galileo probe Neutral Mass Spectrometer experiment (Niemann et al., 1998), and is decreasing in abundance at altitudes above the 10-µbar level, following the prediction from the photochemical model of Moses et al. (2005). The sources of spectral line data and collision-induced absorptions are identical to those described in Fletcher, Orton, et al. (2018), Fletcher, Melin, et al. (2018). The a priori profile of aerosol is a single layer of ammonia ice, with particle radii of 10 ± 5 µm, between 800 and 100-mbar pressure levels with a scale height 0.5 times the gas scale height.

Observational input files for NEMESIS are the pole-to-pole meridian profiles of radiance (Figure 5), which were used to calibrate the individual cylindrical maps as described in Section 2. We remind the reader that for this stage of the observations analysis, the cylindrical maps retain the limb-darkening (or limb-brightening for the 7.9-µm filter), in order to ensure the consistency with the radiance and the emission angle values of each bin for the retrieval calculations. For this purpose, at each latitude point covered by VLT/VISIR, the average value of radiance (calculated to create the pole-to-pole meridian profiles of radiance displayed in orange on Figure 5) is associated to the minimum value of the emission angle across the individual profiles (black dots on Figure 5), in order to assign the pole-to-pole meridional profile to the most central view of the overall data set at that particular latitude point, and to effectively remove longitudinal limb effects. However, a global limb-darkening (or limb-brightening) effect remains when we move toward the pole, corresponding of the highest emission angle view. This poleward high emission angle is taken into account in the retrieval calculation.

NEMESIS uses a non-linear optimal estimation model (and a Levenburg-Marquardt iterative scheme) to adjust the reference atmosphere in order to reduce the differences between the forward-modeled and observed spectra, the process of minimizing the cost function (Irwin et al., 2008; Rodgers, 2000). The cost function represents the relative weight of the assumed atmospheric priors and measurements, and is contained in the calculation of the chi-squared distribution (described in Section 3.3).

**3.2. Vertical Sensitivity**

As expected, meridional variations of the contribution functions of the VISIR filters (Figure 7) reveal a displacement of the peak sensitivity toward lower pressure with increasing latitude (and therefore emission angle) for each filter. This is particularly evident in the Q-Band filters (17.65, 18.72, and 19.50 µm filters) sensing closest
<figure><img src="image_10.png" /><figcaption>**Figure 7.** Meridional variations of the normalized contribution functions of Jupiter calculated from the Very Large Telescope/Very Large Telescope Imager and Spectrometer N-Band ((a): 7.9 and (e–k): 10.77 to 8.59 µm) and Q-Band ((b–d): 19.50, 18.72, and 17.65 µm) filters set based on the varying emission angle.</figcaption></figure>

to the tropopause. However, the 7.90-, 12.27-, and 13.04 µm filter contribution functions show several significant regions peaking at two distinct pressure levels, due to the increasing influence of stratospheric emission at higher emission angles. Hydrocarbons ethane and acetylene contribute to the 12.27 and 13.04 µm contribution functions at high emission angles, particularly poleward of 70°, with contributions peaking at 10 mbar. At lower latitudes, these hydrocarbons provide only a secondary contribution compared to the tropospheric continuum, which is why
<caption>**Table 1**</caption>

Summary of the Conditions of Each of the Retrieval Tests Carried for This Study

<table><thead><tr><th rowspan="2">Retrieval name</th><th rowspan="2">Temperature</th><th rowspan="2">Aerosol profile</th><th colspan="2">Hydrocarbons profiles</th><th>Ammonia profile</th></tr><tr><th>C<sub>2</sub>H<sub>2</sub></th><th>C<sub>2</sub>H<sub>6</sub></th><th>NH<sub>3</sub></th></tr></thead><tbody><tr><td>Temp</td><td>Retrieved</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>Temp Aer</td><td>Retrieved</td><td>Scaling</td><td>–</td><td>–</td><td>–</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2</sub> C<sub>2</sub>H<sub>6</sub></td><td>Retrieved</td><td>Scaling</td><td>Scaling</td><td>Scaling</td><td>–</td></tr><tr><td>Temp Aer NH<sub>3</sub></td><td>Retrieved</td><td>Scaling</td><td>–</td><td>–</td><td>Scaling</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2</sub> C<sub>2</sub>H<sub>6</sub> NH<sub>3</sub></td><td>Retrieved</td><td>Scaling</td><td>Scaling</td><td>Scaling</td><td>Scaling</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2</sub> C<sub>2</sub>H<sub>6,p</sub></td><td>Retrieved</td><td>Scaling</td><td>Scaling</td><td>Parametric</td><td>–</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2,p</sub> C<sub>2</sub>H<sub>6</sub></td><td>Retrieved</td><td>Scaling</td><td>Parametric</td><td>Scaling</td><td>–</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2,p</sub> C<sub>2</sub>H<sub>6,p</sub></td><td>Retrieved</td><td>Scaling</td><td>Parametric</td><td>Parametric</td><td>–</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2,p</sub> C<sub>2</sub>H<sub>6,p</sub> NH<sub>3</sub></td><td>Retrieved</td><td>Scaling</td><td>Parametric</td><td>Parametric</td><td>Scaling</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2</sub> C<sub>2</sub>H<sub>6</sub> NH<sub>3,p</sub></td><td>Retrieved</td><td>Scaling</td><td>Scaling</td><td>Scaling</td><td>Parametric</td></tr><tr><td>Temp Aer NH<sub>3,p</sub></td><td>Retrieved</td><td>Scaling</td><td>–</td><td>–</td><td>Parametric</td></tr><tr><td>Temp Aer C<sub>2</sub>H<sub>2,p</sub> C<sub>2</sub>H<sub>6,p</sub> NH<sub>3,p</sub></td><td>Retrieved</td><td>Scaling</td><td>Parametric</td><td>Parametric</td><td>Parametric</td></tr></tbody></table>

the maps in Figure 1 show tropospheric structure at low latitudes, but stratospheric contributions at high latitudes. In addition, both 10.49 and 10.77-µm filters sense stratospheric ethylene poleward of 80°S, for pressures lowers than 0.01 mbar. Preliminary retrieval tests, using the scaling approach (see following subsection) for ethylene, produced a flat retrieved meridional profile for this species up to ±60° and a large increase peaking at ±80°. Those preliminary tests showed a lack of sensitivity of ethylene up to the polar boundaries for this data set, as suggested by the flat 10.49 and 10.77-µm filter contributions (Figures 7f and 7e, respectively) for the whole latitude range. Hence, to take into account the polar enhancement, we have applied a scaling factor of 18 to the ethylene prior profile of Romani (1996), creating a new ethylene prior profile that fits the VISIR data at all latitudes. In the following retrieval runs, this new ethylene profile is held fixed. By fitting all of the VISIR filters simultaneously, NEMESIS is able to find the best-fitting model to these tropospheric and stratospheric contributions.

### 3.3. Retrieval Sensitivity to Hydrocarbons and Ammonia

Given that temperatures, gases, and aerosols are defined on 120 levels from 10 bars to 1 µbar, this implies a large number of degrees of freedom, and so a large number of variable parameters. Temperature inversions allow the temperatures to vary at every level, albeit with a smoothing assumption imposed by a priori uncertainty to remove non-physical oscillations in retrieved temperatures. Retrieved gases or aerosols either use a scaling of the model profile, or parameterize the vertical structure in some way. Several sensitivity tests (summarized in Table 1) have been performed to assess the best set of retrieval parameters to reproduce the VISIR observations.

The simplest test, fixing the profiles of all gases and aerosols to be uniform with latitude and allowing only temperature to vary, proved incapable of reproducing the VISIR data within the uncertainties. Therefore, we have included aerosols and chemical composition as needed, and we have tested the sensitivity of the inversions to the choice of hydrocarbon and ammonia profiles. In Table 1, two different approaches to retrievals of chemical species have been used, for both, the fitting calculation is made at each latitudinal point assuring a latitudinal variation of chemical species distribution. The “scaling” method allows the retrieval model to increase or decrease the entire profile, while retrieving a continuous temperature profile, in order to better fit the observations. This gives NEMESIS an extra degree of freedom per scaled gas, because both the temperature and the chosen parameter are varying. However, this “scaling” method is assuming a perfect knowledge of the vertical profile, that is, a perfect knowledge about the vertical gradient of this profile, the position of any layer(s) of maximum abundance, and the maximum volume mixing ratio of this chemical parameter, etc.

To increase the degrees of freedom of the NEMESIS calculations, allowing more flexibility in chemical species profiles, we have explored the effect of using “parametric” retrievals of C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>6</sub>, and NH<sub>3</sub> vertical profiles (see Table 1 for a summary of retrieval tests). This is especially needed at high latitudes, where prior measurements
<figure><img src="image_11.png" /><figcaption>**Figure 8.** Latitudinal variations of the $\frac{\chi^2}{N_y}$ parameter to determine the goodness-of-fit for all retrieval tests (summarized in Table 1).</figcaption></figure>

of the vertical distributions are more sparse (Giles et al., 2021; Zhang et al., 2013), and the low-latitude priors are less representative. In this configuration, the retrieval model is able to modify the maximum volume mixing ratio (i.e., mole fraction) of the well-mixed layer of a certain chemical specie, the transition pressure level (referred to as the knee of the profile), and the fractional scale height of the profile. Compared to the “scaling” method, the “parametric” method represents more freedom because chemical profiles change at every altitude, instead of all altitudes by the same amount. For the VLT/VISIR 2018 May data set, we have chosen to parameterize (a) an acetylene distribution with a constant volume mixing ratio of $1.02 \pm 0.8 \times 10^{-5}$ for pressures lower than 0.05 mbar (according Nixon et al. (2007) observations), and a decline with increasing pressure with a fractional scale height of 100 $\pm$ 10; (b) an ethane distribution with a constant volume mixing ratio of $1.62 \pm 0.8 \times 10^{-5}$ (according Nixon et al. (2007) observations) for pressure $p < 0.2$ mbar, and a decline with pressure with a fractional scale height of 2.0 $\pm$ 1.0; and finally (c) an ammonia distribution with a constant volume mixing ratio of $3.62 \pm 0.4 \times 10^{-4}$ (consistent with Juno observations of C. Li et al. (2017)), for pressures higher than 800 $\pm$ 200 mbar, and a decline with altitude with a fractional scale height of 0.15 $\pm$ 1.0. Because of the simple shape of the vertical profiles of $C_2H_2$, $C_2H_6$, and $NH_3$ when the “parametric” retrieval is used, the true vertical distribution of these chemical species is not captured, but this is arguably unnecessary given that we are attempting to fit just a small number (11) of spectral points.

To determine the goodness-of-fit for each test retrieval to fit the observed meridional profiles of radiance (Figure 5), the reduced chi-squared value, $\frac{\chi^2}{N_y}$, is calculated at each latitude point (Figure 8). Here $N_y$ represents the number of spectral points. If the retrieval test (i.e., the combination of temperature, aerosol and chemical species profiles) is a good approximation to the observations, the value of the reduced chi-squared should be approximately unity $\frac{\chi^2}{N_y} = 1$. However, if the fitting “atmosphere” (composed of the prior profiles of temperature, aerosol layer and eventually some chemical species we had allowed to be scaled or modified by the parametric setting) is not appropriate to describe the observations, the value of $\frac{\chi^2}{N_y}$ is greater than 1 because the model is incapable of fitting the data within the measurement uncertainties. Hence, only retrieval tests with $\frac{\chi^2}{N_y} \le 1$ along the larger latitude range are considered as a good fit to the VLT/VISIR 24–27 May 2018 observations. Both **Temp Aer C₂H₂, C₂H₆** and **Temp Aer C₂H₂, C₂H₆, C₂H₃** retrievals (i.e., both with a parametric retrieval approach of acetylene, respectively with and without a scaling of ethane profile) depict a meridional profile of $\chi^2/N_y$ lower or equal to 1 for almost the entire latitude range (see Figure 8). The main benefit of using the parametric approach for acetylene
<figure><img src="image_12.png" /><figcaption>**Figure 9.** Pressure-Latitude cross-section of retrieved temperature from the Very Large Telescope/Very Large Telescope Imager and Spectrometer 24–27 May 2018 data set, superposed with the location of the observed eastward zonal wind (dashed black lines) and westward zonal wind (dotted black lines) peaks (Porco et al., 2003).</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 10.** Cumulative aerosol opacity at 1 bar, superimposed with the location of the observed eastward zonal wind (dashed red lines) and westward zonal wind (dotted red lines) peaks (Porco et al., 2003).</figcaption></figure>

and ethane occurs in polar regions, poleward 50°N and 60°S, where the vertical gradients of hydrocarbons are not well constrained. Indeed, the complex nature of auroral-related chemistry and auroral-related charged particles interaction with the neutral polar atmosphere of Jupiter, as well as the 3D extension of those processes out of the auroral oval remains poorly characterized. The use of the simple shaped of acetylene and ethane vertical profiles through the parametric approach overcomes this lack of vertical constraints, and allow NEMESIS to move away from the prior profiles, particularly well designed from low-latitudes.

To keep the retrieval settings as simple as possible without unnecessary extra parameters, we have selected the Temp Aer C₂H₂,P C₂H₆ test as the best one.

# 4. Zonal-Mean Temperatures, Aerosols, and Composition From Pole to Pole

## 4.1. Temperature and Aerosol Opacity

Retrieved temperatures as a function of latitude and pressure, resulting from the Temp Aer C₂H₂,P C₂H₆ retrieval run, capture most of the upper-tropospheric and stratospheric phenomena on Jupiter (Figure 9). For example, between 10°N and 10°S, we observe a cooling over the Equatorial Zone, directly surrounded by the warm North Equatorial Belt and the South Equatorial Belt (NEB and SEB, ~7 to 17–19° of latitude), and the cold North Tropical Zone and the South Tropical Zone (from 17 to 24°N and from 19 to 26°S of latitude). The high spatial resolution of the VISIR maps reveals that this pattern of cool zones and warm belts continues all the way to the boundary of polar domains (i.e., up to ±60°). In addition to the thermal contrast of the belt/zone signature, the VLT/VISIR data set also captures the aerosol opacity variations, with zones possessing a higher aerosol opacity compared to their neighboring belts, suggesting condensation of saturated vapors in zones and sublimation/evaporation in cloud-free belts (Figure 10). Somewhat surprisingly, the equatorial aerosol opacity is not the largest on the planet, as was observed in previous studies (e.g., Fletcher et al., 2016)—it is possible that the effects of the Equatorial Disturbance with visibly orange cloud cover in 2018–2019 (Antuñano et al., 2020) had reduced the equatorial opacity to lower levels than normal. The transition locations between cold-cloudy zones and warm-cloud-free belts are not clearly seen in this retrieved temperature cross-section, as the retrieval calculations smooth some of the observed features. Nonetheless, by calculating the meridional thermal gradients from the limb-corrected brightness temperature observations for each filter (i.e., from the zonal-mean meridional profiles of brightness temperature calculated from the global maps shown on Figure 1), we can easily assess whether the observed thermal field follows the belts and zones all the way up to the highest latitudes. Figure 11 shows a correlation with the locations of the thermal gradient and zonal jet peaks in the troposphere, particularly clearer for the southern hemisphere (the one facing the Earth when this ground-based observations data set was acquired). In the troposphere, for 17.65 to 8.59-µm filters (Figures 11b–11k) zones have eastward-propagating jets (prograde, their peaks are depicted by dashed lines on Figures 9 and 10) at their polar edges whereas belts exhibit westward-propagating jets (retrograde, their peaks are depicted by dotted lines on Figures 9 and 10) along their polar boundaries.

Moreover, the retrieved temperature cross-section (Figure 9) shows clear cooling poleward of 60°N and 60°S, between 300 and 30 mbar, characteristic of the cold polar vortices in each hemisphere. This is driven primarily by the Q-band observations, and the clear boundary at high latitudes in Figure 1 which is likely to be associated with the highest-latitude jets at 68°. To better emphasize these polar vortex boundaries, we refer to the meridional gradient of brightness temperature for the 17.65-µm filter (Figure 11b), wavelength for which the polar vortices is best defined on the global maps. In the southern hemisphere, the poleward cooling occurs at the equatorward edge of the southernmost westward jet, that is, at 67°S, up to the pole. For the northern hemisphere, the location of the polar vortices is less evident.
<figure><img src="image_14.png" /><figcaption>**Figure 11.** Meridional profiles of brightness temperature gradient calculated from the Very Large Telescope/Very Large Telescope Imager and Spectrometer global maps for each filter, superimposed with the location of the observed eastward zonal wind (dashed lines) and westward zonal wind (dotted lines) peaks (Porco et al., 2003).</figcaption></figure>

the 7.9-µm filter, the northernmost poleward cooling occurs at the northernmost westward jet location (64°N), whereas the 17.65-µm filter depicts this cooling at second northernmost eastward jet location (62°N). The aerosol distributions in the polar domains are somewhat asymmetric in cloud coverage (Figure 10). There is a net decrease of the northern aerosol opacity, about 0.5 in the north, whereas the southern pole retains an aerosol opacity of about 0.6, implying increased aerosol opacity over the southern pole compared to the northern one, though the north and south aerosol optical depths are equal within the retrieval uncertainties.

Comparison with flyby observations of the Voyager-1/IRIS and Cassini/CIRS spectrometers, as well as ground-based observations by the IRTF/TEXES instrument (Figure 12), shows an overall consistency between our retrieval results and previous studies. In the equatorial stratosphere, the retrievals reveal a warm temperature anomaly in the 0.5–5.0 mbar range centered at the equator, surrounded by two cooler anomalies centered at ±15° latitude (Figure 12a). Conversely, flyby observations from Voyager-1/IRIS in 1979 and Cassini/CIRS in 2000/2001, as well as IRTF/TEXES measurements in 2014 (Fletcher et al., 2016; Melin et al., 2018; Nixon et al., 2010), depict a cold equatorial region at the 0.5-mbar pressure level, and a relatively uniform meridional contrast of the equatorial stratosphere in the Gemini/TEXES measurements of March 2017 (Fletcher, Orton, et al., 2020). The transition from cold to warm equatorial stratospheric temperatures between 2014 and 2018, along with the off-equatorial thermal anomalies near ±15°, are the manifestations of Jupiter's equatorial “Quasi-Quadrennial Oscillation” (Antuñano et al., 2021; Cosentino et al., 2017, 2020; Friedson, 1999; Leovy et al., 1991; Orton et al., 1991; Simon-Miller et al., 2007). An asymmetric temperature changing is also present in the sub-equatorial regions (from 8 to 20°), transitioning from warm to cold anomalies of temperature, with a much clearer and stronger change in the northern sub-equatorial region. The downward progression of the equatorial stratospheric oscillation requires more than just the May 2018 snapshot, and will be the topic of forthcoming studies.

The stratospheric temperature in the southern hemisphere does not capture the usual meridional variations at the 0.5-mbar and 5-mbar pressure levels shown in Figures 12a and 12b. At 0.5 mbar, the retrieved temperature from VLT/VISIR measurements varies from 20°S to 65°S with an almost constant gradient, without showing the large decrease of about 10–20 K from 35°S to 60°S as shown in Voyager-1/IRIS, Cassini/CIRS and IRTF/TEXES profiles.

At 5 mbar, the temperature of the southern hemisphere from 40°S to 70°S is around 5 K warmer than previous studies, with a flat variation over latitude. Moreover, the stratospheric northern mid-latitudes, between 35 and 60°N, show local warm regions in the VLT/VISIR profiles at 5 mbar, centered at 40 and 55°N (Figure 12b). Those warm regions are not consistent with previous observations, but this could well be the signature of stratospheric mid-latitude variability associated with the propagation of planetary-scale waves (as a Rossby planetary-scale wave, mentioned in Section 2 and shown on Figure 3).

From 70°N to 70°S, VLT/VISIR temperatures have the same variations in the troposphere as previous observations from Voyager-1/IRIS, and especially from Cassini/CIRS and IRTF/TEXES (Figures 12c and 12d). Both 100-mbar and 300-mbar pressure levels reveal a cold Equatorial Zone surrounded by the warm North and South Equatorial Belts, producing a 7 K-amplitude variation in the meridional profile of temperature from 20°N to 20°S. Temperatures consistently follow the Cassini/CIRS observations at 300 mbar, but its variability from 20°N to 20°S is amplified in the VLT/VISIR observations at 100 mbar compared to those from IRTF and spacecraft facilities, most likely a consequence of the higher spatial resolution of our observations. Another difference
<figure><img src="image_15.png" /><figcaption>**Figure 12.** Zonal-mean retrieved temperatures at four pressure levels spanning the troposphere and stratosphere from the Very Large Telescope/Very Large Telescope Imager and Spectrometer 24–27 May 2018 data set, compared with observations from Voyager/IRIS, Cassini/CIRS, and IRTF/TEXES.</figcaption></figure>

occurring at low latitudes in the VLT/VISIR observations is the local maximum of temperature at 25°S, producing an increased temperature of 3–4 K, which is not seen in the other data sets.

## 4.2. Zonal Wind Shear

The retrieved zonal-mean temperatures and their meridional gradients can be used to estimate the vertical shear on the zonal winds, using thermal wind equation (Equation 1):

$$ \frac{\partial \bar{u}}{\partial z} = - \frac{g}{f \bar{T}} \times \frac{\partial \bar{T}}{\partial y} \quad (1) $$

where $\bar{u}$ is the zonal-mean zonal wind, $g$ is the gravitational acceleration, $f$ is Coriolis parameter, $\bar{T}$ is the zonal-mean temperature and $y$ the north-south distance in kilometres (Figure 13). This approximation is not applicable to equatorial region, as the Coriolis parameter $f$ approaches zero. Therefore, we have omitted tropical regions equatorward of 6° of latitude.

In the lower to middle stratosphere, there is clear correlation between the location of the zonal jets defined by the dotted and dashed lines. This correlation results in zones on the equatorward sides of the eastward jet and belts on their poleward sides; and zones on the poleward side of the westward jets, with belts on their equatorward side, between 500 mbar to the tropopause (~100 mbar). The correlation also appears to be somewhat stronger in the southern hemisphere than in the north, confirming the pattern highlighted in previous studies using Juno Microwave Radiometer data (Fletcher et al., 2021).

## 4.3. Meridional Distribution of Hydrocarbons

Retrieved hydrocarbons as a function of latitude, resulting from the Temp Aer $C_2H_{2,p}$ $C_2H_6$ retrieval run, capture most of the meridional variability of previous work (Figure 14). Compared to those studies, the VLT/VISIR observations are within the range of previous observations from several facilities, and is particularly consistent with the IRTF/TEXES 2017 data set from Melin et al. (2018). Between 60°S and 40°N, acetylene distribution retrieved from the VLT/VISIR data set describes an almost flat gradient, with a variability not larger than $2 \times 10^6$. To correctly fit the VLT/VISIR observations at

all latitudes with a $\chi^2/N_y$ less than 1, we have to adopt the $C_2H_2$ parametric and $C_2H_6$ scaling retrieval technique, particularly for the high-latitude regions (poleward of 60°). However, the best fits to the data imply polar enhancements of almost an order of magnitude for $C_2H_2$, which has not been seen in previous retrieval analyses to date (Figure 14). This is needed because the temperature-only fit (Figure 15, blue line, based largely on the 7.9-µm brightness) produces a stratospheric temperature that is too cool to explain the observed emission in the ethane- and acetylene-sensing filters (i.e., 12.27- and 13.04-µm filters), so the abundances have to increase significantly to compensate.

However, the large enhancement of volume mixing ratio in high-to-polar latitudes is not found in the meridional distribution of ethane, where a scaling retrieval settings was enough to fit the observations (i.e., with a $\chi^2/N_y$ less than 1 for the whole latitude range). Global meridional variations of ethane, from 70°S to 70°N exhibit a slight increase of volume mixing ratio toward the higher latitudes. This is consistent with Voyager and Cassini previous observations, albeit quite reduced. This is particularly true for the northernmost latitudes, producing an asymmetry in the high latitude concentration of ethane. This asymmetry might simply result from the observational conditions, that is, the sub-observer point at -3.76° offered a better view of the southern pole.
<figure><img src="image_16.png" /><figcaption>**Figure 13.** 2D cross-section of zonal-mean zonal wind shear calculated from the Very Large Telescope/Very Large Telescope Imager and Spectrometer retrieved temperature using Equation 1, superposed with the location of the observed eastward zonal wind (dashed black lines) and westward zonal wind (dotted black lines) peaks (Porco et al., 2003). The color scale is a symmetric logarithmic normalization to emphasize gradients at mid and high latitudes. Tropical regions equatorward of 6° are omitted.</figcaption></figure>

In the high latitude to polar region, the vertical structure of hydrocarbons is still rather poorly known, as well as their interactions with the auroral-related particle precipitation, their photochemical transformations, their transport across the polar vortex, etc. It is possible that our form of parameterization is simply inappropriate for the polar domain. Although the bright polar emission at 13 µm (Figure 5h) is most readily explained by a significant increase in acetylene abundance at high latitudes, this is not supported by previous measurements, and points to the extreme challenge of constraining polar temperatures and hydrocarbons using filtered imaging alone.

**5. Structure of the Great Red Spot in 2018**

The VLT/VISIR 24–27 May 2018 data set offers excellent coverage of the GRS, in particular on the night of 26 May, and it provides an opportunity to study its thermal and cloud structures. Thanks to the diffraction-limited filtered imaging at high sensitivity for a wavelength range of 4.82–19.5 µm of the VISIR plate-scale (0.045"/pixel), and using the Data Reduction Manager pipeline, we have interpolated the radiance maps onto a 0.5-degree grid, defined as the same across all filters, which oversamples the longest wavelengths. Hence, from a single set of images that captures the best view of the GRS during the night of 26 May 2018, we have selected an area of 20°-latitude by 40°-longitude centered at latitude 20°S–longitude 157°W System III (coordinates of GRS center in May 2018), shown on a 0.5 × 0.5° grid in Figure 16. We have made a retrieval calculation for each single pixel in this area, permitting a longitude-latitude resolved retrieval of the GRS.

**5.1. Interior Structure of the Great Red Spot**

Retrieved temperatures over the GRS (Figure 17) from the VLT/VISIR data shows that the GRS is a cold anti-cyclonic feature, but with the continued existence of a tropospheric “warm spot” on the inner edge of the core at 21°S, 153°W System III, suggesting that the warm spot might be long-lived but varies over short timescales, potentially related to the visibility of the red core observed in the amateur observation images in Figure 2. The location of this “warm spot” is possibly related with the location of where the tangential winds of the GRS stagnate and even reverse to become cyclonic (Fletcher et al., 2010). Also evident in the radiance maps (Figures 16f–16k), the localized “warm spot” is consistent with previous retrievals from mid-IR imaging data (Fletcher et al., 2010). However, the “warm spot” in the core is not seen at the tropopause levels, from the 180-mbar to the 80-mbar pressure levels, where the contrast shows predominantly a cool core with a warm periphery (Figures 17b and 17c); nor in the stratospheric 5-mbar pressure level, where the GRS shape is barely distinguishable (Figure 17a). From 380 to 600 mbar, this “warm spot” appears to drift eastward, from 157 to 153°W System III with increasing pressure
<figure><img src="image_17.png" /><figcaption>**Figure 14.** Retrieved meridional profiles of hydrocarbons at 1 mbar from the Very Large Telescope/Very Large Telescope Imager and Spectrometer 24–27 May 2018 data set for the **Temp Aer C<sub>2</sub>H<sub>2,p</sub> C<sub>2</sub>H<sub>6</sub>** (black) retrieval runs.</figcaption></figure>

(Figures 17d–17k), behavior also noticed in radiance maps (Figures 16e–16j). The largest contrast of the “warm spot” occurs at 550 mbar, with a maximum value of ~150 K and a contrast of 5–7 K warmer over the inner coldest temperatures. At this location, the aerosol distribution shows a depletion of aerosols (Figure 18). The localized warming sensed at the cloud-top level (Figure 16k) and obtained in the retrieved temperature maps may result in evaporation of any condensed ices there, implying a relatively cloud-free region on the southern inner edge of the GRS, at least at the 500–700 mbar level.

The core of the GRS at 550 mbar represents the coldest part of this region by ~10 K, reflecting the intense upwelling that is characteristic of the GRS. Regarding the aerosol distribution resulting from the retrieval calculations (Figure 18) shows that the coldest parts of the GRS core are correlated with some of the highest aerosol opacities in the southern tropics. This is likely due to enhanced condensation of aerosols at low temperatures, or due to the production of photochemical aerosols (i.e., the red chromophore) entrained by the peripheral jet of the
<figure><img src="image_18.png" /><figcaption>**Figure 15.** Comparison of observed (orange) and retrieved meridional profiles of radiance for three case tests: **Temp** (in blue), **Temp Aer C₂H₂ C₂H₆** (in dark orange), and **Temp Aer C₂H₂,ₚ C₂H₆** (in green) retrieval runs to highlight the need for the parametric retrieval approach for hydrocarbons to better fit the southern auroral-related increase in the radiance profiles.</figcaption></figure>

GRS, confirmed by the visible amateur observations showing three different regions of reddish color (Figure 2). In visible light, the core of the GRS is composed of a central area of dark red chromophores, surrounded by a dark orange area, which is finally encircled by dark red chromophores, with the close match to the VISIR aerosol map suggesting a clear distinction between these three regions based on temperature (i.e., three different regions of condensation, and/or production of photochemical aerosols).

The warm southern periphery varies from 145 K at 440 mbar to 157 K at 550 mbar, up to ~5 K warmer than the surrounding Southern Tropical Zone. This region of increased warming on the southern edge of the GRS is one of the warmest features in the region, beginning within the annulus at the 380-mbar level and extending beyond
<figure><img src="image_19.png" /><figcaption>**Figure 16.** Great Red Spot radiance maps for Very Large Telescope/Very Large Telescope Imager and Spectrometer (24–27 May 2018) N-Band (7.9–13.04 µm) and Q-Band (19.50, 18.72, and 17.65 µm) observations.</figcaption></figure>

the southern rim of the vortex to the cloud-top level (Figures 17d–17k). As with the tropospheric aerosol opacity obtained with VISIR in 2006–2008 observations (Fletcher et al., 2010), the VISIR 2018 observations reveal a well-defined lane of depleted aerosols around the GRS periphery (Figure 18). The aerosol lane depletion also corresponds to a thin line of cooling in temperature maps, splitting the warm southern periphery around the 500-mbar level in two warm peripheries and afterward acting as a barrier between the actual GRS periphery and this thin warm line wrapping around the GRS for the deepest pressure levels.

## 5.2. Great Red Spot Environs

The complex interaction between the eastward and westward jets bordering the SEB, and the anticyclonic annulus of the GRS, leads to turbulent rifting northwest of the GRS in a region called the GRS wake. At this time,
<figure><img src="image_20.png" /><figcaption>**Figure 17.** Great Red Spot retrieved temperature maps from Very Large Telescope/Very Large Telescope Imager and Spectrometer 26 May 2018 data set.</figcaption></figure>

visible-light observations also showed an unusual dark feature ("South Tropi-cal Disturbance") on the west side of the GRS, through which turbulence was streaming southward then eastward around the GRS (Figure 2). This appears as a warm extension of the SEB in Figures 16 and 17. The wake region displays a range of temperature contrasts related to small-scale plumes in the local region of 0.5–1 K at 440 mbar, but higher at 80 mbar the region exhibits little spatial contrast in temperature. The regions of greatest aerosol depletion are in the South Equatorial Belt (SEB) directly to the east and west of the GRS and co-located with the warmest temperatures (South Equatorial Belts lane) and strong vertical mixing (GRS wake). The perennial turbulence in the GRS wake creates chaotic structures of upward and downward motion (cooling and warming air) resulting in changes in aerosol opacity. This activi-ity in the South Equatorial Belt is observed from the 10.77 to 8.59-µm images (Figures 16e–16k, respectively) as strong variations in flux, implying strong aerosol clearing and production.

The thermal field at 5 mbar (Figure 17a) displays regions of elevated tempera-ture in the SEB immediately north-east and north-west of the GRS, with peak temperatures at 15 and 17°S, each ~10°-wide in longitude and estimated to be at 170 K, ~4 K warmer than the surroundings. They lie on both sides of

the northern periphery of the GRS, with the western warm spot directly on top of the GRS wake. It is possible that this warm stratospheric band is being influenced by the anticyclone in the troposphere below. Thermal waves near the tropopause and in the lower stratosphere can be generated by tropospheric meteorology and convective plumes (Andrews et al., 1987) and disruption of flows around vortices (L. Li et al., 2006). It is plausible that these stratospheric hot spots are the result of intense convection and turbulent mixing in the troposphere that generates atmospheric waves that propagate vertically and break at some critical altitude depositing their kinetic energy into these higher altitudes as thermal energy, warming the region. The stratospheric temperatures above the GRS have not been previously studied (Fletcher et al., 2010) and would benefit from a systematic study over multiple epochs to see if this structure of warm stratospheric perturbations is a persistent feature.

# 6. Polar Dynamics

Observing the polar regions of Jupiter via Earth-based facilities is a significant challenge, as they are viewed at an oblique angle with a large emission angle, inducing strong limb brightening or darkening at the planetary limbs. To highlight the polar atmospheric features, a limb-darkening correction (described in Section 2.3) has been applied to the global maps. In this section we characterize the polar domain of Jupiter and compare to Juno/JunoCam observations of the polar hazes ("polar hoods") acquired during the same period.

## 6.1. Jupiter's Cold Polar Vortices

The zonal organization of the high latitudes is different between the two hemispheres, as seen in both Figures 19 and 20. These polar-projection maps show a very structured southern hemisphere with the characteristic banded structure persisting up to the southern jet S6 (following the nomenclature of Rogers et al. (2022)) at 64°S in the upper troposphere and stratosphere. In comparison, the northern pole begins to show similar small-scale struc-ture beyond the westward jet located at 68°N at the tropopause (80 mbar, in Figure 19b), and exhibits intense wave activity that dominates in the strato-sphere (Figure 19a).

The view of the southern pole is dominated by the southern aurora, seen primarily in the filters associated with emission lines of CH₄ (7.90 µm, indicative of warming in Figure 20a), C₂H₄ (10.77, 10.49, and 9.82 µm in Figures 20e, 20f, and 20i), C₂H₂ (13.04 µm in Figure 20h), and C₂H₆ (12.27 and 13.04 µm in Figures 20g and 20h). The increased brightness temperature for 10.77, 10.49, 12.27, 13.04, and 9.82-µm filters can either be explained

<figure><img src="image_21.png" /><figcaption>**Figure 18.** Great Red Spot map of the cumulative aerosol optical depth at 1 mbar from Very Large Telescope/Very Large Telescope Imager and Spectrometer 26 May 2018 data set retrieval calculations.</figcaption></figure>
<figure><img src="image_22.png" /><figcaption>**Figure 19.** (a–k) Northern equidistant polar projections of the Very Large Telescope/Very Large Telescope Imager and Spectrometer 24–27 May 2018 global radiance maps, corrected for limb brightening/darkening. At this epoch, the southern hemisphere of Jupiter was facing the Earth, hence the highest northern latitudes (poleward 80°N) have been cut off in the northern polar projection due to extreme emission angle in this data set and proximity to the edge of the disc (by 5°). Moreover, because of the interruption of the observations during the night of 24th–25th due to strong winds, a large part of the planet between 210 and 270°W System III is missing in these polar maps for seven of the 11 filters used here (7.9, 17.65, 18.72, 19.5, 12.27, 13.04, and 8.99 µm filters). (l) JunoCam CH₄-band (889 nm) and (m) visible RGB observations of Jupiter's north pole during the Perijove 13, processed by Gerald Eichstädt and John Rogers (Rogers et al., 2022). Longitude coordinates are displayed in System III W longitude.</figcaption></figure>

by enhanced heating, or potentially indicate an enhancement of hydrocarbon production from the ion-neutral chemical breakdown of CH₄. Considering the north pole, there is a slight increase of the mid-infrared emission in the 7.90, 12.27, and 13.04-µm filters between 120°W System III and 210°W System III, and poleward the 70°N
<figure><img src="image_23.png" /><figcaption>**Figure 20.** (a–k) Southern equidistant polar projection of the Very Large Telescope/Very Large Telescope Imager and Spectrometer 24–27 May 2018 global maps, corrected for limb brightening/darkening. (l) JunoCam CH₄-band (889 nm) and (m) visible RGB observations of Jupiter's north pole during the Perijove 13, processed by Gerald Eichstädt and John Rogers (Rogers et al., 2022). Longitude coordinates are displayed in System III W longitude.</figcaption></figure>

parallel (Figures 19a, 19g, and 19h). Nonetheless, we do not consider this to represent the presence of auroral heating in the northern hemisphere, since the area is wider, and the heat signature is more diffuse and not as bright as in the southern hemisphere. The northern auroral emission is known to change over short timescales (Sinclair, Orton, et al., 2019), and the May 2018 observations may have caught the north pole during a period when auroral heating was absent.
Moreover, this missing northern aurora signature enables a clear view of the northern cold polar vortex (Fletcher et al., 2016; Kunde et al., 2004; Orton et al., 2002, 2008; Porco et al., 2003). The low temperatures over both poles in the upper troposphere and stratosphere show that the cooling persists from 1 mbar (Figures 19h and 20h) to ~5 mbar (Figures 19a and 20a) consistent with the aerosol cooling effect due to the large optical thickness and the fractal-aggregate shapes of the polar aerosols (one to two orders of magnitude optically thicker than the lower latitude haze), as described by Zhang et al. (2013). To investigate the relation between the cold polar vortex and Jupiter's polar aerosols, we compare to JunoCam observations of the polar region acquired during the VLT/VISIR run (perijove 13, 25 May 2018).

The general appearance of the poles in the JunoCam visible observations is bluish with discrete white features (Orton et al., 2017; Rogers et al., 2022), co-located with bright structures in the CH₄ band, implying that these reflective storm systems are located at higher altitudes than the surrounding less reflective regions (Figures 19m and 20m). This transition boundary to the polar region is seen in the JunoCam near-IR (Figures 19l and 20l) as a large CH₄-bright region extending poleward of 50-60°N (with a ragged boundary in the north) and poleward of ~64°S (more discrete boundary in the south). This polar boundary meanders with longitude (possibly modulated by the presence of a Rossby wave, L. Li et al. (2004), Barrado-Izagirre et al. (2008), Rogers et al. (2022)) in JunoCam visible observations, which is not captured in the VLT/VISIR observations.

However, despite the limited 889-nm view of the north polar aerosols from JunoCam (Figure 19l), there does not seem to be a strong correlation with the northern cold polar vortex boundary and the hazes. Indeed, the northern cold polar vortex appears to be more confined to higher latitudes (Figures 19b and 19d). The correlation between the JunoCam aerosols and the cold polar vortex is much clearer in the south (at ~67°S, Figure 20), where the tropospheric cooling is colocated with the reflective aerosols at 889 nm, and with the dark blue polar domain in the RGB image. This strong correlation in the south, and weak correlation in the north, could potentially be explained by an asymmetry in the aerosol populations at the two poles (Guerlet et al., 2020; Zhang et al., 2013). If the aerosols are generated via ion-neutral chemistry within the auroral ovals, the fact that the south cold polar vortex completely encircles the compact south polar auroral oval means that those aerosols could be constrained by the vortex boundary acting as a transport barrier. Conversely, the northern auroral oval extends outside of the cold polar vortex, meaning that polar aerosols would not be entrained as efficiently by the vortex. This asymmetry in polar aerosols was also observed by Zhang et al. (2013) in their study of aerosols derived from Cassini observations of Jupiter.

The radiative contribution of Jupiter's polar aerosols was discussed by Guerlet et al. (2020) using a 1-D seasonal radiative-convective model, confirming the large contribution of the stratospheric polar aerosol in the radiative budget. Depending on the optical properties of these aerosols (which remain uncertain), the authors showed that the maximum net impact of stratospheric aerosol is located between 5 and 30 mbar at 45-60°. In their model, they also show a significant cooling poleward 65°, consistent with the present VISIR data set.

## 6.2. Mid/High-Latitude Vortices

The polar projections also provide a means for identifying discrete features at Jupiter's mid-latitudes that may be classified by their long-lived structure, features like Oval BA (~30°S), the Anticyclonic White Ovals (AWOs, 35-37°S) and S4-LRS-1 (~56°S), using the classical nomenclature Rogers (1995). All of these anticyclones are associated with low brightness temperatures in VLT/VISIR 19.5, 10.77, and 8.59 µm filters, suggestive of cold-core features above the clouds (Figures 20d, 20e, and 20k; also seen in 9.82, 8.99 µm filters in Figures 20i and 20j). They appear as white or reddish features in JunoCam visible and CH₄-band observations (Figure 20m, denoted by red circles, and Figure 20l), suggesting that white aerosols (ices) are condensing in the cold upper parts of these anticyclones. The sensing through several wavelengths both in visible and infrared wavelengths argue that the structure of these anticyclones persists with height, with subtle changes of shape. Indeed, at the 500-750 mbar cloud-top level, the VLT/VISIR observations at 8.99 µm exhibit very low radiance, correlated with the location of the thick cloud cover at 1-4 bar seen by de Pater et al. (2011), with a bright peripheral ring of negligible cloud opacity as well. The associated cooler temperatures of this specific aerosol structure extend all the way to the tropopause (Figure 20b, corresponding to the 17.65-µm filter). As well as the anticyclonic ovals, the maps show a pale quiescent circulation just North-East of it at ~50-70°W (the "South Temperate Belt Specter"). This is dark at 889-nm (Figure 20l) and warm at 8.99-10.77 µm (Figures 20j and 20e, respectively).
These mid-latitude features provide some insight into the smaller white ovals observed in the polar regions by JunoCam. Some of these smaller white ovals (between 70 and 80°S) exhibit spiral extensions (seen in the Juno/JunoCam observations in Figure 20m) that indicates their anticyclonic motion, although many lack this structure, giving little indication of their direction of rotation. Some of those that display anticyclonic motion are co-located with cloudy regions at 2–4 bar, implying similar overall structure to the larger white ovals at mid-latitudes, albeit on a smaller scale. The VLT/VISIR maps suggest that the vertical structure of these AWOs is similar in both hemispheres.

Apart from the anticyclones, the polar regions of both hemispheres exhibit amorphous cyclonic structures referred to as “Folded Filamentary Regions” (FFR, using the nomenclature of Ingersoll et al. (1984), one of them is pointed by the yellow arrow on Figure 20m). These regions are among the brightest and largest discrete features in the polar regions and have been previously observed by Voyager, Cassini, Hubble and Juno (Barrado-Izagirre et al., 2008; L. Li et al., 2004; Porco et al., 2003; Rogers et al., 2022). In the south, several FFRs are located in a band between 65°S and 72°S (Rogers et al., 2022; Figure 20). These regions of chaotic flow, like the AWOs, are highly reflective in the methane band, implying elevated cloud tops, although probably lower than the polar hoods, which may represent enhancement of lower stratospheric aerosols consistent with the expected distribution of aerosols at the poles (Zhang et al., 2013). The FFRs have associated structure at depth, deep cloud opacity that is modulated by their cyclonic motion (Ingersoll et al., 1984). Identification of discrete structures beyond 70°S in the other tropospheric mid-IR filters is challenging due to the proximity to the limb and the general cold temperatures of the vortex in which they are embedded. Nevertheless, the FFRs generally appear to be warmer than their surroundings and cloud-free in the mid-IR, consistent with their identification as cyclonic, stormy regions in visible imaging. Even with the excellent spatial resolution afforded by VLT/VISIR, diagnosing the thermal conditions within these high-latitude features remains extremely difficult without mid-IR capabilities on an orbiting spacecraft.

## 7. Temporal Changes in the Southern Aurora

Along the 80°S parallel (Figure 21), there is a large temporal evolution of the observed radiance over the southern auroral region (0°–60° and 300°–360° System III West longitude), that is also inferred in the zonally averaged profiles of radiance (Figure 5). This time evolution is mainly observed in the methane emission band filter 7.9 µm, ethylene ($C_2H_4$) and acetylene ($C_2H_2$) emission band filters (10.49, 10.77, and 13.04 µm), and ethane ($C_2H_6$) emission band filters 12.27 µm, as well as the 9.82 µm filter (Figures 21a and 21e–21i, respectively). Brightness variability of the aurora is so large for the 7.9, 10.49, 13.04, and 9.82 µm filters from one night to the next that this produces discontinuities along the 80°S parallel profiles of radiance for these filters. In particular, on the edges of the aurora location such as ~320°W (Figures 21f and 21i), 300°W (Figure 21a), and 90°W (Figure 21h).

To follow the average time variation of the thermal aurora signature in this mid-infrared data set, we have gathered the images per night of observation (i.e., from day *i*th, 11 p.m. to day (*i* + 1)th, 7 a.m.). For each VLT/VISIR filter, we have averaged the data from 0° to 60° and from 300° to 360° longitude System III West along a 2°-latitude band centered at 80°S. These two data bins correspond to the maximum emission of the aurora as depicted in the zonal profiles of radiance in Figure 21. This regional averaging creates a single spectral point per filter to characterize the average atmospheric response of the aurora event during the four observing nights. However, the second night of observation, from 24 May 11 p.m. to 25 May 7 a.m., had to be shortened due to bad weather, and therefore only two filters constitute this nightly data set (8.59 and 10.77 µm filters). In addition, the observing night 24 May from 1 to 7 a.m. is also a reduced data set of 9 filters (7.9, 19.5, 10.49, 10.77, 12.27, 13.04, 9.82, 8.99, and 8.59 µm). So, to keep retrieval calculation consistent from one night to the next, we have only considered the first, third and fourth nights of observation (i.e., 24 May, 25–26 May, and 26–27 May in what follows), with a spectral data set only composed of the 9 shared filters (i.e., excluding the 17.65 and 18.72 µm filters).

For this particular retrieval, the reference atmosphere is composed by the same prior as the zonal mean study above (see Section 3).

The observed radiance from the 24 to 27 May decreased with time for most of the wavelengths sensing the temperature and hydrocarbons species in the stratosphere (Figure 22). Most of the retrieved radiance profiles
<figure><img src="image_24.png" /><figcaption>**Figure 21.** Night-colored-coded longitudinal radiance profiles along the 80°S parallel for the entire data set retaining the limb-darkening/brightening effect for Very Large Telescope/Very Large Telescope Imager and Spectrometer N-Bands (7.9 and 10.77 to 8.59 µm) and Q-Bands (19.50, 18.72, and 17.65 µm).</figcaption></figure>

for the nine selected wavelengths are within the 5% error envelope and so are quite well fitted, in particular the stratospheric temperature 7.9-µm filter, the tropospheric aerosol opacity 8.99 and 8.59-µm filters. Only the 12.27 and 13.04-µm filters, sensing the stratospheric ethane and acetylene, as well as the 10.49 and 10.77-µm filters, sensing the stratospheric high latitude ethylene distribution, are not well retrieved, even with the addition of the scaling of C₂H₄ profile for the retrieval calculations. Considering the high emission angle of those data, this radiance fitting is the best we could obtain.

The retrieved temperature profiles for the three nights between the 24 and 27 May 2018 show a significant cooling, by almost 20 K, in the stratosphere over time (Figure 23). If we assume this cooling is just the effect of temperature variation, it implies a cooling times of a few hours that are unrealistically short at these pressures. So it is therefore more likely that some kind of direct non-LTE (local thermal equilibrium) effects are adding to the regular LTE emission, allowing these things to appear to change on very short timescales. That would imply the VLT/VISIR observation is not truly measuring the temperatures of these regions. Regarding the contribution function of each VLT/VISIR filters at 80°S (Figure 7), it is challenging to determine which chemical species are responsible for the stratospheric cooling. Emission from the dominant hydrocarbons, ethane and acetylene, and to a lesser extent methane and ethylene, could result in radiative time constants that are as short as a few hours at the very highest altitudes over the poles, allowing the neutral atmosphere to cool down following an injection of
<figure><img src="image_25.png" /><figcaption>**Figure 22.** Observed and retrieved radiance time profiles for the averaged aurora area during the three selected nights.</figcaption></figure>

auroral energy over a short timespan. Brightening and dimming of the southern auroral emission was observed over comparable timescales in 2017 by Subaru/COMICS Sinclair, Orton, et al. (2019).

The solar wind activity predictions of a uni-dimensional idealized magnetohydrodynamic model for Jupiter (Tao et al., 2005) have been analyzed to look for auroral events during May 2018. Calculated in a heliocentric frame, with measurement of the solar wind flow around the Earth as inputs, the prediction of the model is at its most accurate when the target planet is close to opposition, which for Jupiter was on 8 May 2018 (Earth-Sun-Jupiter angle). On 23 May 2018, Jupiter was describing, with the OMNI spacecraft, an angle of -2° on the heliocentric longitude frame, which implies a maximum of prediction accuracy (Zieger & Hansen, 2008). Between the 20 and 21 May 2018, the model predicts an enhancement of the solar wind dynamical pressure by 0.85 nPa in the jovian environment, followed by a period of quiescent conditions (Figure 24). This solar wind event may have perturbed the magnetosphere, transiently
<figure><img src="image_26.png" /><figcaption>**Figure 23.** (a) Retrieved temperature profiles and (b) deviation from the prior profiles ($T_{\text{retrieved}} - T_{\text{prior}}$) over the aurora area for each of the three selected nights.</figcaption></figure>

<figure><img src="image_27.png" /><figcaption>**Figure 24.** Predicted solar wind conditions in 2018, calculated from the OMNI-measured conditions at Earth, and the 1-D model by Tao et al. (2005) to propagate and predict the solar wind flow at Jupiter.</figcaption></figure>

heating the upper atmosphere through higher rates of particle precipitation and/or Joule heating driven by stronger Pedersen currents (Badman et al., 2015; Grodent et al., 2001; Yates et al., 2014). Even with the timing uncertainty, the VLT/VISIR observations from May 24th to the 27th may have captured the subsequent cooling of the southern auroral emission after this solar wind compression event. It is unclear why the northern auroral oval did not brighten in response to the same compression event, hinting that not all compression responses are equal.

## 8. Conclusions

Global pole-to-pole ground-based mid-infrared VLT/VISIR maps of Jupiter, spanning 5–20 µm, were obtained on the VLT on 24–27 May 2018. These represent the highest quality mid-infrared maps acquired by VISIR during a program of ground-based support for NASA's Juno mission since 2016, and thus they provide our best coverage of the cold polar vortices and auroral activity. A pipeline for destriping, cleaning, calibrating and projecting the data was designed, and applied to all data of 24 to 27 May 2018 (raw data are available on the ESO Science Archive Facilities website http://archive.eso.org/eso/eso_archive_main.html, and the processed data are available to the community in our open-access archive, Bardet, 2023), with findings spanning multiple data sets to be detailed in forthcoming studies. From this map in 2018, we draw the following conclusions:

*   **Belts and Zones:** Jupiter's banded structure of cool zones and warm belts extends from the equator to the edge of the polar vortices, with a strong correlation between the maximum vertical windshear (from temperature gradients) and the locations of Jupiter's zonal jets. The zonal jets decay throughout the upper tropospheric levels (80–600 mbar) sensed by the VISIR data. Peaks in aerosol opacity sometimes occur within the cool zones (suggestive of condensation of saturated vapors), but the correlation between aerosol opacity and the zonal jet structure is weaker, confirming that aerosols are not a good proxy for Jupiter's belts and zones.

*   **Equatorial Oscillation:** A warm equatorial peak near 1–4 mbar, and associated off-equatorial minima in stratospheric temperatures, reveal the presence of Jupiter's equatorial stratospheric oscillation (sometimes called the QQO). The presence of the warm equatorial band in 7.9 µm imaging in 2018 is consistent with the downward propagation of the wave pattern shown by Giles et al. (2020) in the year after a 2017 disruption.

*   **Hydrocarbon Distributions:** Although Jupiter's low latitudes can be fitted with a horizontally uniform distribution of ethane and acetylene, this is not true at high latitudes, where enhancements of both ethane and acetylene are required (these hydrocarbons have more significant contributions at the higher emission angles). Hence, as already suggested by previous studies, these enhancements of hydrocarbons reinforce the evidence of enhanced ion-related chemistry in Jupiter's auroral regions.

*   **Cold Polar Vortices:** The banded structure of low/mid-latitudes gives way to cold polar vortices at both poles in the upper troposphere, and over the north pole in the stratosphere, for whose the latitudinal boundaries are located at 67°S and 64°N, but the southern stratosphere is somewhat masked by auroral emission (see below). The southern polar vortex coincides with reflective aerosols observed in the CH$_4$ band at 890 nm by JunoCam, and with the blue coloration in visible light, suggesting polar aerosols entrained by the vortex. In the north, the aerosol field is more diffuse and not as well correlated with the edges of the cold polar vortex. The cold vortices are likely due to radiative cooling associated with these aerosols, entrained dynamically by the northernmost and southernmost jet streams.
* Auroral Heating: The southern auroral oval was bright in the mid-infrared in May 2018 (although the northern oval was less visible), where the influx of energetic electrons and ions from the jovian magnetosphere and external solar-wind environment cause warming in the stratosphere. A solar wind compression is expected to have reached Jupiter immediately before the VISIR observations, and over four consecutive nights of observations VISIR captured the subsequent cooling of the southern auroral region, from the 24 to 27 May 2018. Despite this evidence of an interaction between the magnetosphere and stratosphere in Jupiter's polar region, there is currently no clear picture of how the particle precipitation inside the aurora oval interacts with the lower atmosphere, in terms of chemical and dynamical processes.

* Anticyclones and Cyclones: The high spatial resolution provided by VLT/VISIR resolves vortices of many different sizes, from the small white ovals and FFR at high latitudes, to larger white anticyclones at mid-latitudes, to Oval BA and the GRS. A prominent brown barge is observed to be bright in the SEB, indicating warm, cloud-free and volatile-depleted conditions within these cyclones. Mid-infrared observations probe altitudes above vortex midplanes in the deeper troposphere, so anticyclones are cold, and cyclones warm, consistent with the decay of their tangential velocities with altitude. Detailed characterization of the GRS confirms previous studies, with a small warm core embedded within the larger cold vortex, and complex rifting in the surroundings. The GRS may influence the stratospheric temperatures near 5 mbar, with warm patches immediately northeast and northwest of the vortex, possibly associated with upward-propagating wave activity.

The May 2018 VISIR observations provide only a snapshot of Jupiter's atmosphere, but demonstrate a wealth of phenomena that could be monitored over time using the 2016–2022 VISIR time series. To further understand the links between the auroral regions, the chemistry of the surrounding polar atmosphere and the mid-latitude regions, from the magnetosphere to the troposphere, we require longitudinally resolved and time variable ion-neutral photochemical model of Jupiter's high latitudes, coupled with a global climate model. Although coupled chemistry and transport models do exist, the inclusion of auroral contributions, both of the hydrocarbons and of the aerosols responsible for radiative cooling, is needed to improve our knowledge of Jupiter's polar atmosphere.

## Data Availability Statement

The NEMESIS radiative transfer and spectral retrieval tool (Irwin et al., 2008) is open-access and is available for download (Irwin & Teanby, 2022). The processed data of May 2018 observations are available here (Bardet, 2023), and the Python program used to calibrate, map the data, as well as create the input files for NEMESIS and plot the retrieval results is available here (Bardet & Donnelly, 2023).

## References

* Achterberg, R. K., Conrath, B. J., & Gierasch, P. J. (2006). Cassini CIRS retrievals of ammonia in Jupiter's upper troposphere. *Icarus*, *182*(1), 169–180. https://doi.org/10.1016/j.icarus.2005.12.020

* Andrews, D. G., Holton, J. R., & Leovy, C. B. (1987). *Middle atmosphere dynamics*. Academic Press.

* Antuñano, A., Cosentino, R. G., Fletcher, L. N., Simon, A. A., Greathouse, T. K., & Orton, G. S. (2021). Fluctuations in Jupiter's equatorial stratospheric oscillation. *Nature Astronomy*, *5*(1), 71–77. https://doi.org/10.1038/s41550-020-1165-5

* Antuñano, A., Fletcher, L. N., Orton, G. S., Toledo, D., Melin, H., Roman, M. T., et al. (2020). Characterizing temperature and aerosol variability during Jupiter's 2006–2007 equatorial zone disturbance. *Journal of Geophysical Research (Planets)*, *125*(10), e06413. https://doi.org/10.1029/2020JE006413

* Badman, S. V., Branduardi-Raymont, G., Galand, M., Hess, S. L. G., Krupp, N., Lamy, L., et al. (2015). Auroral processes at the Giant planets: Energy deposition, emission mechanisms, morphology and spectra. *Space Science Reviews*, *187*(1–4), 99–179. https://doi.org/10.1007/s11214-014-0042-x

* Bardet, D. (2023). Jupiter's ground-based observations on 2018 May 24th–27th from the Very Large Telescope Imager and Spectrometer Instrument. *Zenodo*. https://doi.org/10.5281/zenodo.8401816

* Bardet, D., & Donnelly, P. (2023). PTDonnelly/ground_based: Codebase for data reduction and retrieval processing for Bardet et al. (2023). *Zenodo*. https://doi.org/10.5281/zenodo.10053810

* Barrado-Izagirre, N., Sánchez-Lavega, A., Pérez-Hoyos, S., & Hueso, R. (2008). Jupiter's polar clouds and waves from Cassini and HST images: 1993–2006. *Icarus*, *194*(1), 173–185. https://doi.org/10.1016/j.icarus.2007.08.025

* Caldwell, J., Tokunaga, A. T., & Gillett, F. C. (1980). Possible infrared aurorae on Jupiter. *Icarus*, *44*(3), 667–675. https://doi.org/10.1016/0019-1035(80)90135-9

* Caldwell, J., Tokunaga, A. T., & Orton, G. S. (1983). Further observations of 8-µm polar brightenings of Jupiter. *Icarus*, *53*(1), 133–140. https://doi.org/10.1016/0019-1035(83)90026-X

* Cavalié, T., Benmahi, B., Hue, V., Moreno, R., Lellouch, E., Fouchet, T., et al. (2021). First direct measurement of auroral and equatorial jets in the stratosphere of Jupiter. *Astronomy & Astrophysics*, *647*, L8. https://doi.org/10.1051/0004-6361/202140330

## Acknowledgments

Bardet, Fletcher, Antuñano, Roman, and Melin were supported by a European Research Council Consolidator Grant (under the European Union's Horizon 2020 research and innovation program, grant agreement no 723890) at the University of Leicester. Donnelly acknowledges funding from Agence Nationale de la Recherche (ANR), project EMERGIANT ANR-17-CE31-0007. Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This research used the ALICE High Performance Computing Facility at the University of Leicester. This paper is based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programme 0101.C-0073(A). We wish to thank the many ESO telescope operators and support staff who work long nights to provide the community with the data needed to better understand Jupiter. For the purpose of Open Access, the corresponding author has applied a CC-BY public copyright licence to any Author Accepted Manuscript (AAM) version arising from this submission.
Cavalié, T., Fletcher, L., Krupp, N., Masters, A., & Witasse, O. (2017). Exploration of Jupiter's atmosphere and magnetosphere with the European Jupiter Icy Moons Explorer (JUICE). In *European planetary science congress*, 11, EPSC2017-420.

Chaufray, J. Y., Greathouse, T. K., Gladstone, G. R., Waite, J. H., Maillard, J. P., Majeed, T., et al. (2011). Spectro-imaging observations of Jupiter's 2 µm auroral emission. II: Thermospheric winds. *Icarus*, 211(2), 1233-1241. https://doi.org/10.1016/j. icarus.2010.11.021

Conrath, B. J., Gierasch, P. J., & Leroy, S. S. (1990). Temperature and circulation in the stratosphere of the outer planets. *Icarus*, 83(2), 255-281.
https://doi.org/10.1016/0019-1035(90)90068-k

Conrath, B. J., Gierasch, P. J., & Ustinov, E. A. (1998). Thermal structure and para hydrogen fraction on the outer planets from voyager IRIS measurements. *Icarus*, 135(2), 501-517. https://doi.org/10.1006/icar.1998.6000

Conrath, B. J., & Pirraglia, J. A. (1983). Thermal structure of Saturn from Voyager infrared measurements: Implications for atmospheric dynamics. *Icarus*, 53(2), 286-292. https://doi.org/10.1016/0019-1035(83)90148-3

Cosentino, R. G., Greathouse, T., Simon, A., Giles, R., Morales-Juberías, R., Fletcher, L. N., & Orton, G. (2020). The effects of waves on the meridional thermal structure of Jupiter's stratosphere. *The Planetary Science Journal*, 1(3), 63. https://doi.org/10.3847/PSJ/abbda3

Cosentino, R. G., Morales-Juberías, R., Greathouse, T., Orton, G., Johnson, P., Fletcher, L. N., & Simon, A. (2017). New observations and modeling of Jupiter's quasi-quadrennial oscillation. *Journal of Geophysical Research (Planets)*, 122(12), 2719-2744. https://doi.org/10.1002/2017JE005342

Deming, D., Mumma, M. J., Espenak, F., Jennings, D. E., Kostiuk, T., Wiedemann, G., et al. (1989). A search for p-mode oscillations of Jupiter: Serendipitous observations of nonacoustic thermal wave structure. *Astrophysical Journal*, 343, 456. https://doi.org/10.1086/167719

Deming, D., Reuter, D., Jennings, D., Bjoraker, G., McCabe, G., Fast, K., & Wiedemann, G. (1997). Observations and analysis of longitudinal thermal waves on Jupiter. *Icarus*, 126(2), 301-312. https://doi.org/10.1006/icar.1996.5658

de Pater, I., Sault, R. J., Butler, B., DeBoer, D., & Wong, M. H. (2016). Peering through Jupiter's clouds with radio spectral imaging. *Science*. https://doi.org/10.1126/science.aaf2210

de Pater, I., Sromovsky, L. A., Hammel, H. B., Fry, P. M., LeBeau, R. P., Rages, K., et al. (2011). Post-equinox observations of Uranus: Berg's evolution, vertical structure, and track towards the equator. *Icarus*, 215(1), 332-345. https://doi.org/10.1016/j. icarus.2011.06.022

Donnelly, P. T. (2021). Variability of Jovian meteorology from ground-based mid-infrared observations. https://doi.org/10.25392/leicester.data.14931891.v1

Drossart, P., Bezard, B., Atreya, S. K., Bishop, J., Waite, J. H., & Boice, D. (1993). Thermal profiles in the auroral regions of Jupiter. *Journal of Geophysical Research*, 98(E10), 18803-18812. https://doi.org/10.1029/93JE01801

Duer, K., Gavriel, N., Galanti, E., Kaspi, Y., Fletcher, L. N., Guillot, T., et al. (2021). Evidence for multiple ferrel-like cells on Jupiter. *Geophysical Research Letters*, 48(23), e95651. https://doi.org/10.1029/2021GL095651

Flasar, F. M., & Gierasch, P. J. (1986). Mesoscale waves as a probe of Jupiter's deep atmosphere. *Journal of the Atmospheric Sciences*, 43(22), 2683-2707. https://doi.org/10.1175/1520-0469(1986)043(2683:MWAAPO)2.0.CO;2

Flasar, F. M., Kunde, V. G., Achterberg, R. K., Conrath, B. J., Simon-Miller, A. A., Nixon, C. A., et al. (2004). An intense stratospheric jet on Jupiter. *Nature*, 427(6970), 132-135. https://doi.org/10.1038/nature02142

Fletcher, L. N., de Pater, I., Reach, W. T., Wong, M., Orton, G. S., Irwin, P. G. J., & Gehrz, R. D. (2017). Jupiter's para-H₂ distribution from SOFIA/FORCAST and Voyager/IRIS 17-37 µm spectroscopy. *Icarus*, 286, 223-240. https://doi.org/10.1016/j. icarus.2016.10.002

Fletcher, L. N., Orton, G., Sinclair, J., Guerlet, S., Read, P., Antuñano, A., et al. (2018). A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex. *Nature Communications*, 9(1), 3564. https://doi.org/10.1038/s41467-018-06017-3

Fletcher, L. N., Greathouse, T. K., Orton, G. S., Sinclair, J. A., Giles, R. S., Irwin, P. G. J., & Encrenaz, T. (2016). Mid-infrared mapping of Jupiter's temperatures, aerosol opacity and chemical distributions with IRTF/TEXES. *Icarus*, 278, 128-161. https://doi.org/10.1016/j. icarus.2016.06.008

Fletcher, L. N., Guerlet, S., Orton, G. S., Cosentino, R. G., Fouchet, T., Irwin, P. G. J., et al. (2017). Disruption of Saturn's quasi-periodic equatorial oscillation by the great northern storm. *Nature Astronomy*, 1(11), 765-770. https://doi.org/10.1038/s41550-017-0271-5

Fletcher, L. N., Kaspi, Y., Guillot, T., & Showman, A. P. (2020). How well do we understand the belt/zone circulation of giant planet atmospheres? *Space Science Reviews*, 216(2), 30. https://doi.org/10.1007/s11214-019-0631-9

Fletcher, L. N., Melin, H., Adriani, A., Simon, A. A., Sanchez-Lavega, A., Donnelly, P. T., et al. (2018). Jupiter's mesoscale waves observed at 5 µm by ground-based observations and Juno JIRAM. *Astronomical Journal*, 156(2), 67. https://doi.org/10.3847/1538-3881/ace02

Fletcher, L. N., Orton, G. S., Greathouse, T. K., Rogers, J. H., Zhang, Z., Oyafuso, F. A., et al. (2020). Jupiter's equatorial plumes and hot spots: Spectral mapping from Gemini/TEXES and Juno/MWR. *Journal of Geophysical Research (Planets)*, 125(8), e2020JE006399. https://doi.org/10.1029/2020JE006399

Fletcher, L. N., Orton, G. S., Mousis, O., Yanamandra-Fisher, P., Parrish, P. D., Irwin, P. G. J., et al. (2010). Thermal structure and composition of Jupiter's Great Red Spot from high-resolution thermal imaging. *Icarus*, 208(1), 306-328. https://doi.org/10.1016/j. icarus.2010.01.005

Fletcher, L. N., Orton, G. S., Sinclair, J. A., Donnelly, P., Melin, H., Rogers, J. H., et al. (2017). Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival. *Geophysical Research Letters*, 44(14), 7140-7148. https://doi.org/10.1002/2017GL073383

Fletcher, L. N., Orton, G. S., Yanamandra-Fisher, P., Fisher, B. M., Parrish, P. D., & Irwin, P. G. J. (2009). Retrievals of atmospheric variables on the gas giants from ground-based mid-infrared imaging. *Icarus*, 200(1), 154-175. https://doi.org/10.1016/j. icarus.2008.11.019

Fletcher, L. N., Oyafuso, F. A., Allison, M., Ingersoll, A., Li, L., Kaspi, Y., et al. (2021). Jupiter's temperate belt/zone contrasts revealed at depth by Juno microwave observations. *Journal of Geophysical Research (Planets)*, 126(10), e2021JE006858. https://doi.org/10.1029/2021JE006858

Friedson, A. J. (1999). New observations and modelling of a QBO-like oscillation in Jupiter's stratosphere. *Icarus*, 137(1), 34-55. https://doi.org/10.1006/icar.1998.6038

Gierasch, P. J., Conrath, B. J., & Magalhães, J. A. (1986). Zonal mean properties of Jupiter's upper troposphere from voyager infrared observations. *Icarus*, 67(3), 456-483. https://doi.org/10.1016/0019-1035(86)90125-9

Giles, R. S., Fletcher, L. N., & Irwin, P. G. J. (2017). Latitudinal variability in Jupiter's tropospheric disequilibrium species: GeH₄, AsH₃ and PH₃. *Icarus*, 289, 254-269. https://doi.org/10.1016/j. icarus.2016.10.023

Giles, R. S., Greathouse, T. K., Cosentino, R. G., Orton, G. S., & Lacy, J. H. (2020). Vertically-resolved observations of Jupiter's quasi-quadrennial oscillation from 2012 to 2019. *Icarus*, 350, 113905. https://doi.org/10.1016/j. icarus.2020.113905

Giles, R. S., Greathouse, T. K., Hue, V., Gladstone, G. R., Melin, H., Fletcher, L. N., et al. (2021). Meridional variations of C₂H₂ in Jupiter's stratosphere from Juno UVS observations. *Journal of Geophysical Research (Planets)*, 126(8), e06928. https://doi.org/10.1029/2021JE006928

Giles, R. S., Hue, V., Greathouse, T. K., Gladstone, G. R., Kammer, J. A., Versteeg, M. H., et al. (2023). Enhanced C₂H₂ absorption within Jupiter's southern Auroral oval from Juno UVS observations. *Journal of Geophysical Research (Planets)*, 128(2), e2022JE007610. https://doi.org/10.1029/2022JE007610
Grassi, D., Adriani, A., Mura, A., Atreya, S. K., Fletcher, L. N., Lunine, J. I., et al. (2020). On the spatial distribution of minor species in Jupiter's troposphere as inferred from Juno JIRAM data. *Journal of Geophysical Research (Planets)*, 125(4), e2019JE006206. https://doi.org/10.1029/2019JE006206

Griffith, C. A., Bézard, B., Greathouse, T., Lellouch, E., Lacy, J., Kelly, D., & Richter, M. J. (2004). Meridional transport of HCN from SL9 impacts on Jupiter. *Icarus*, 170(1), 58–69. https://doi.org/10.1016/j.icarus.2004.02.006

Grodent, D., Waite, J., Hunter, J., & Gérard, J.-C. (2001). A self-consistent model of the Jovian auroral thermal structure. *Journal of Geophysical Research*, 106(A7), 12933–12952. https://doi.org/10.1029/2000JA900129

Guerlet, S., Spiga, A., Delattre, H., & Fouchet, T. (2020). Radiative-equilibrium model of Jupiter's atmosphere and application to estimating stratospheric circulations. *Icarus*, 351, 113935. https://doi.org/10.1016/j.icarus.2020.113935

Holton, J. R. (2004). *An introduction to dynamic meteorology* (4th ed., p. 48). Elsevier Academic Press.

Hue, V., Hersant, F., Cavalié, T., Dobrijevic, M., & Sinclair, J. A. (2018). Photochemistry, mixing and transport in Jupiter's stratosphere constrained by Cassini. *Icarus*, 307, 106–123. https://doi.org/10.1016/j.icarus.2018.02.018

Ingersoll, A. P. (2020). Cassini exploration of the planet Saturn: A comprehensive review. *Space Science Reviews*, 216(8), 122. https://doi.org/10.1007/s11214-020-00751-1

Ingersoll, A. P., Beebe, R. F., Conrath, B. J., & Hunt, G. E. (1984). Structure and dynamics of Saturn's atmosphere. In T. Gehrels & M. S. Matthews (Eds.), *Saturn* (pp. 195–238).

Irwin, P. G. J., & Teanby, N. (2022). nemesiscode/nemesiscode.github.io: NEMESIS Documentation Website. *Zenodo*. https://doi.org/10.5281/zenodo.5816724

Irwin, P. G. J., Teanby, N. A., de Kok, R., Fletcher, L. N., Howett, C. J. A., Tsang, C. C. C., et al. (2008). The NEMESIS planetary atmosphere radiative transfer and retrieval tool. *Journal of Quantitative Spectroscopy & Radiative Transfer*, 109(6), 1136–1150. https://doi.org/10.1016/j.jqsrt.2007.11.006

Kim, S. J., Caldwell, J., Rivolo, A. R., Wagener, R., & Orton, G. S. (1985). Infrared polar brightening on Jupiter III. Spectrometry from the Voyager 1 IRIS experiment. *Icarus*, 64(2), 233–248. https://doi.org/10.1016/0019-1035(85)90088-0

Kostiuk, T., Romani, P., Espenak, F., Livengood, T. A., & Goldstein, J. J. (1993). Temperature and abundances in the Jovian auroral stratosphere 2. Ethylene as a probe of the microbar region. *Journal of Geophysical Research*, 98(E10), 18823–18830. https://doi.org/10.1029/93JE01332

Kunde, V. G., Flasar, F. M., Jennings, D. E., Bézard, B., Strobel, D. F., Conrath, B. J., et al. (2004). Jupiter's atmospheric composition from the Cassini thermal infrared spectroscopy experiment. *Science*, 305(5690), 1582–1587. https://doi.org/10.1126/science.1100240

Lagage, P. O., Pel, J. W., Authier, M., Belorgey, J., Claret, A., Doucet, C., et al. (2004). Successful commissioning of VISIR: The mid-infrared VLT instrument. *The Messenger*, 117, 12–16.

Lellouch, E., Bézard, B., Strobel, D. F., Bjoraker, G. L., Flasar, F. M., & Romani, P. N. (2006). On the HCN and CO₂ abundance and distribution in Jupiter's stratosphere. *Icarus*, 184, 478–497. https://doi.org/10.1016/j.icarus.2006.05.018

Leovy, C. B., Friedson, A. J., & Orton, G. S. (1991). The quasiquadrennial oscillation of Jupiter's equatorial stratosphere. *Nature*, 354(6352), 380–382. https://doi.org/10.1038/354380a0

Li, C., Ingersoll, A., Janssen, M., Levin, S., Bolton, S., Adumitroaie, V., et al. (2017). The distribution of ammonia on Jupiter from a preliminary inversion of Juno microwave radiometer data. *Geophysical Research Letters*, 44(11), 5317–5325. https://doi.org/10.1002/2017GL073159

Li, L., Ingersoll, A. P., & Huang, X. (2006). Interaction of moist convection with zonal jets on Jupiter and Saturn. *Icarus*, 180(1), 113–123. https://doi.org/10.1016/j.icarus.2005.08.016

Li, L., Ingersoll, A. P., Vasavada, A. R., Porco, C. C., Del Genio, A. D., & Ewald, S. P. (2004). Life cycles of spots on Jupiter from Cassini images. *Icarus*, 172(1), 9–23. https://doi.org/10.1016/j.icarus.2003.10.015

Livengood, T. A., Kostiuk, T., Espenak, F., & Goldstein, J. J. (1993). Temperature and abundances in the Jovian auroral stratosphere I. Ethane as a probe of the Millibar region. *Journal of Geophysical Research*, 98(E10), 18813–18822. https://doi.org/10.1029/93JE01043

Lord, S. (1992). A new software tool for computing Earth's atmospheric transmission of near-and far-infrared radiation. In *NASA technical memorandum*, 103957,94035-1000.

Melin, H., Fletcher, L. N., Donnelly, P. T., Greathouse, T. K., Lacy, J. H., Orton, G. S., et al. (2018). Assessing the long-term variability of acetylene and ethane in the stratosphere of Jupiter. *Icarus*, 305, 301–313. https://doi.org/10.1016/j.icarus.2017.12.041

Moreno, R., Marten, A., Matthews, H. E., & Biraud, Y. (2003). Long-term evolution of CO, CS and HCN in Jupiter after the impacts of comet Shoemaker-Levy 9. *Planetary and Space Science*, 51(9–10), 591–611. https://doi.org/10.1016/S0032-0633(03)00072-2

Moses, J. I., Fouchet, T., Bézard, B., Gladstone, G. R., Lellouch, E., & Feuchtgruber, H. (2005). Photochemistry and diffusion in Jupiter's stratosphere: Constraints from ISO observations and comparisons with other giant planets. *Journal of Geophysical Research (Planets)*, 110(E8), 8001. https://doi.org/10.1029/2005JE002411

Niemann, H. B., Atreya, S. K., Carignan, G. R., Donahue, T. M., Haberman, J. A., Harpold, D. N., et al. (1998). The composition of the Jovian atmosphere as determined by the Galileo probe mass spectrometer. *Journal of Geophysical Research*, 103(12), 22831–22846. https://doi.org/10.1029/98JE01050

Nixon, C. A., Achterberg, R. K., Conrath, B. J., Irwin, P. G. J., Teanby, N. A., Fouchet, T., et al. (2007). Meridional variations of $C_2H_2$ and $C_2H_6$ in Jupiter's atmosphere from Cassini CIRS infrared spectra. *Icarus*, 188(1), 47–71. https://doi.org/10.1016/j.icarus.2006.11.016

Nixon, C. A., Achterberg, R. K., Romani, P. N., Allen, M., Zhang, X., Teanby, N. A., et al. (2010). Abundances of Jupiter's trace hydrocarbons from Voyager and Cassini. *Planetary and Space Science*, 58(13), 1667–1680. https://doi.org/10.1016/j.pss.2010.05.008

Orsolini, Y., & Leovy, C. B. (1993). A model of large-scale instabilities in the jovian troposphere. I. Linear model. *Icarus*, 106(2), 392–405. https://doi.org/10.1006/icar.1993.1180

Orton, G. S., Antuñano, A., Fletcher, L. N., Sinclair, J. A., Momary, T. W., Fujiyoshi, T., et al. (2022). Unexpected long-term variability in Jupiter's tropospheric temperatures. *Nature Astronomy*, 7(2), 190–197. https://doi.org/10.1038/s41550-022-01839-0

Orton, G. S., Fisher, B. M., Baines, K. H., Momary, T. W., & Fox, O. D. (2002). A cold hole at the pole of Jupiter. In *AAS/division for planetary sciences meeting abstracts* (Vol. 34, p. 13.01).

Orton, G. S., Fisher, B. M., Baines, K. H., Stewart, S. T., Friedson, A. J., Ortiz, J. L., et al. (1998). Characteristics of the Galileo probe entry site from Earth-based remote sensing observations. *Journal of Geophysical Research*, 103(E10), 22791–22814. https://doi.org/10.1029/98JE02380

Orton, G. S., Friedson, A. J., Caldwell, J., Hammel, H. B., Baines, K. H., Bergstrahl, J. T., et al. (1991). Thermal maps of Jupiter—Spatial organization and time dependence of stratospheric temperatures, 1980 to 1990. *Science*, 252(5005), 537–542. https://doi.org/10.1126/science.252.5005.537

Orton, G. S., Friedson, A. J., Yanamandra-Fisher, P. A., Caldwell, J., Hammel, H. B., Baines, K. H., et al. (1994). Spatial organization and time dependence of Jupiter's tropospheric temperatures, 1980–1993. *Science*, 265(5172), 625–631. https://doi.org/10.1126/science.265.5172.625

Orton, G. S., Hansen, C., Caplinger, M., Ravine, M., Atreya, S., Ingersoll, A. P., et al. (2017). The first close-up images of Jupiter's polar regions: Results from the Juno mission JunoCam instrument. *Geophysical Research Letters*, 44(10), 4599–4606. https://doi.org/10.1002/2016GL072443
Orton, G. S., Yanamandra-Fisher, P. A., Fisher, B. M., Friedson, A. J., Parrish, P. D., Nelson, J. F., et al. (2008). Semi-annual oscillations in Saturn's low-latitude stratospheric temperatures. *Nature*, **453**(7192), 196-199. https://doi.org/10.1038/nature06897

Pirraglia, J. A. (1989). Dissipationless decay of Jovian jets. *Icarus*, **79**(1), 196-207. https://doi.org/10.1016/0019-1035(89)90116-4

Pirraglia, J. A., Conrath, B. J., Allison, M. D., & Gierasch, P. J. (1981). Thermal structure and dynamics of Saturn and Jupiter. *Nature*, **292**(5825), 677-679. https://doi.org/10.1038/292677a0

Porco, C. C., West, R. A., McEwen, A., Del Genio, A. D., Ingersoll, A. P., Thomas, P., et al. (2003). Cassini imaging of Jupiter's atmosphere, satellites, and rings. *Science*, **299**(5612), 1541-1547. https://doi.org/10.1126/science.1079462

Read, P. L., Gierasch, P. J., Conrath, B. J., Simon-Miller, A., Fouchet, T., & Yamazaki, Y. H. (2006). Mapping potential-vorticity dynamics on Jupiter. *I: Zonal-Mean circulation from Cassini and voyager 1 data*. *Quarterly Journal of the Royal Meteorological Society*, **132**(618), 1577-1603. https://doi.org/10.1256/qj.05.34

Rego, D., Achilleos, N., Stallard, T., Miller, S., Prangé, R., Dougherty, M., & Joseph, R. D. (1999). Supersonic winds in Jupiter's aurorae. *Nature*, **399**(6732), 121-124. https://doi.org/10.1038/20121

Rodgers, C. D. (2000). *Inverse methods for atmospheric remote sounding: Theory and practice*. World Scientific.

Rogers, J. H. (1995). *The giant planet Jupiter*. Cambridge University Press.

Rogers, J. H., Eichstädt, G., Hansen, C. J., Orton, G. S., Momary, T., Casely, A., et al. (2022). Flow patterns of Jupiter's south polar region. *Icarus*, **372**, 114742. https://doi.org/10.1016/j.icarus.2021.114742

Romani, P. N. (1996). Recent rate constant and product measurements of the reactions C₂H₃ + H₂ and C₂H₃ + H—Importance for photochemical modeling of hydrocarbons on Jupiter. *Icarus*, **122**(2), 233-241. https://doi.org/10.1006/icar.1996.0122

Romani, P. N., Bishop, J., Bezard, B., & Atreya, S. (1993). Methane photochemistry on Neptune—Ethane and acetylene mixing ratios and haze production. *Icarus*, **106**(2), 442-463. https://doi.org/10.1006/icar.1993.1184

Seiff, A., Kirk, D. B., Knight, T. C. D., Young, R. E., Mihalov, J. D., Young, L. A., et al. (1998). Thermal structure of Jupiter's atmosphere near the edge of a 5-µm hot spot in the north equatorial belt. *Journal of Geophysical Research*, **103**(E10), 22857-22890. https://doi.org/10.1029/98JE01766

Showman, A. P., & de Pater, I. (2005). Dynamical implications of Jupiter's tropospheric ammonia abundance. *Icarus*, **174**(1), 192-204. https://doi.org/10.1016/j.icarus.2004.10.004

Simon-Miller, A. A., Conrath, B. J., Gierasch, P. J., Orton, G. S., Achterberg, R. K., Flasar, F. M., & Fisher, B. M. (2006). Jupiter's atmospheric temperatures: From Voyager IRIS to Cassini CIRS. *Icarus*, **180**(1), 98-112. https://doi.org/10.1016/j.icarus.2005.07.019

Simon-Miller, A. A., Poston, B. W., Orton, G. S., & Fisher, B. (2007). Wind variations in Jupiter's equatorial atmosphere: A QQQ counterpart? *Icarus*, **186**(1), 192-203. https://doi.org/10.1016/j.icarus.2006.08.009

Sinclair, J. A., Lisse, C. M., Orton, G. S., Krishnamoorthy, M., Fletcher, L. N., Hora, J., et al. (2023). A retrospective analysis of mid-infrared observations of the Comet D/Shoemaker-Levy 9 and Wesley impacts on Jupiter. *Icarus*, **394**, 115404. https://doi.org/10.1016/j.icarus.2022.115404

Sinclair, J. A., Moses, J. I., Hue, V., Greathouse, T. K., Orton, G. S., Fletcher, L. N., & Irwin, P. G. J. (2019). Jupiter's auroral-related stratospheric heating and chemistry III: Abundances of C₂H₄, CH₃C₂H, C₄H₂ and C₆H₆ from Voyager-IRIS and Cassini-CIRS. *Icarus*, **328**, 176-193. https://doi.org/10.1016/j.icarus.2019.03.012

Sinclair, J. A., Orton, G. S., Fernandes, J., Kasaba, Y., Sato, T. M., Fujiyoshi, T., et al. (2019). A brightening of Jupiter's auroral 7.8-µm CH₄ emission during a solar-wind compression. *Nature Astronomy*, **3**(7), 607-613. https://doi.org/10.1038/s41550-019-0743-x

Sinclair, J. A., Orton, G. S., Greathouse, T. K., Fletcher, L. N., Moses, J. I., Hue, V., & Irwin, P. G. J. (2017). Jupiter's auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra. *Icarus*, **292**, 182-207. https://doi.org/10.1016/j.icarus.2016.12.033

Sinclair, J. A., Orton, G. S., Greathouse, T. K., Fletcher, L. N., Moses, J. I., Hue, V., & Irwin, P. G. J. (2018). Jupiter's auroral-related stratospheric heating and chemistry II: Analysis of IRTF-TEXES spectra measured in December 2014. *Icarus*, **300**, 305-326. https://doi.org/10.1016/j.icarus.2017.09.016

Tao, C., Kataoka, R., Fukunishi, H., Takahashi, Y., & Yokoyama, T. (2005). Magnetic field variations in the Jovian magnetotail induced by solar wind dynamic pressure enhancements. *Journal of Geophysical Research*, **110**(A11), A11208. https://doi.org/10.1029/2004JA010959

Yates, J. N., Achilleos, N., & Guio, P. (2014). Response of the Jovian thermosphere to a transient 'pulse' in solar wind pressure. *Planetary and Space Science*, **91**, 27-44. https://doi.org/10.1016/j.pss.2013.11.009

Zhang, X., West, R. A., Banfield, D., & Yung, Y. L. (2013). Stratospheric aerosols on Jupiter from Cassini observations. *Icarus*, **226**(1), 159-171. https://doi.org/10.1016/j.icarus.2013.05.020

Zieger, B., & Hansen, K. C. (2008). Statistical validation of a solar wind propagation model from 1 to 10 AU. *Journal of Geophysical Research (Space Physics)*, **113**(A8), A08107. https://doi.org/10.1029/2008JA013046