cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.48577/jpl.qczip4
title: Molecular composition of short-period comets from millimetre-wave spectroscopy: 21P/Giacobini-Zinner, 38P/Stephan-Oterma, 41P/Tuttle-Giacobini-Kresák and 64P/Swift-Gehrels

description: We present the results of millimetre-wave spectroscopic observations and spectral surveys of the following short-period comets: 41P/Tuttle-Giacobini-Kresák in April 2017, 21P/Giacobini-Zinner in September 2018, 38P/Stephan-Oterma and 64P/Swift-Gehrels in December 2018, carried out with the IRAM 30-m radio telescope at wavelengths between 1 and 3 mm. Comet 21P was also observed in November 1998 with the IRAM 30-m, JCMT and CSO radio telescopes at wavelengths from 0.8 to 3 mm. The abundances of the following molecules have been determined in those comets: HCN and CH3OH in 41P, CH3OH in 38P, HCN, CH3OH and CS in 64P, and HCN, CH3OH, CS, H2CO, CH3CN and H2S in comet 21P. The first three comets, classified as carbon-chain typical from visible spectro-photometry, are relatively rich in methanol (3.5 to 5% relative to water). On the other hand, comet 21P, classified as carbon-chain depleted, shows abundances relative to water which are low for methanol (1.7%), very low for H2S (0.1%) and also relatively low for H2CO (0.16%) and CO (&lt;2.5%). Observations of comet 21P do not show any change in activity and composition between the 1998 and 2018 perihelions. Sensitive upper limits on the abundances of other molecules of interest are also reported for these comets.
DOI: 10.48577/jpl.v8zujb
title: Vertical Strucure and Color of Jovian Latitudinal Cloud Bands during the Juno Era

description: The identity of the coloring agent(s) in Jupiter’s atmosphere and the exact structure of Jupiter’s uppermost cloud deck are yet to be conclusively understood. The Crème Brûlée model of Jupiter’s tropospheric clouds, originally proposed by Baines et al. and expanded upon by Sromovsky et al. and Baines et al., presumes that the chromophore measured by Carlson et al. is the singular coloring agent in Jupiter’s troposphere. In this work, we test the validity of the Crème Brûlée model of Jupiter’s uppermost cloud deck using spectra measured during the Juno spacecraft’s fifth perijove pass in 2017 March. These data were obtained as part of an international groundbased observing campaign in support of the Juno mission using the New Mexico State University Acousto-optic Imaging Camera at the 3.5 m telescope at Apache Point Observatory in Sunspot, NM, USA. We find that the Crème Brûlée model cloud-layering scheme can reproduce Jupiter’s visible spectrum both with the Carlson et al. chromophore and with modifications to its imaginary index of refraction spectrum. While the Crème Brûlée model provides reasonable results for regions of Jupiter’s cloud bands such as the North Equatorial Belt and Equatorial Zone, we find that it is not a safe assumption for unique weather events, such as the 2016–2017 Southern Equatorial Belt outbreak that was captured by our measurements.
DOI: 10.48577/jpl.wixjvl
title: High-resolution UV/optical/IR imaging of Jupiter in 2016–2019

description: Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53 days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14 filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm. We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near 35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data. Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the 15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The HST data maps multiple concentric polar hoods of high-latitude hazes.
DOI: 10.48577/jpl.wjhkqr
title: Global Estimates of Land Surface Water Fluxes from SMOS and SMAP Satellite Soil Moisture Data

description: In-depth knowledge about the global patterns and dynamics of land surface net water flux (NWF) is essential for quantification of depletion and recharge of groundwater resources. Net water flux cannot be directly measured, and its estimates as a residual of individual surface flux components often suffer from mass conservation errors due to accumulated systematic biases of individual fluxes. Here, for the first time, we provide direct estimates of global NWF based on near-surface satellite soil moisture retrievals from the Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) satellites. We apply a recently developed analytical model derived via inversion of the linearized Richards’ equation. The model is parsimonious, yet yields unbiased estimates of long-term cumulative NWF that is generally well correlated with the terrestrial water storage anomaly from the Gravity Recovery and Climate Experiment (GRACE) satellite. In addition, in conjunction with precipitation and evapotranspiration retrievals, the resultant NWF estimates provide a new means for retrieving global infiltration and runoff from satellite observations. However, the efficacy of the proposed approach over densely vegetated regions is questionable, due to the uncertainty of the satellite soil moisture retrievals and the lack of explicit parameterization of transpiration by deeply rooted plants in the proposed model. Future research is needed to advance this modeling paradigm to explicitly account for plant transpiration.
DOI: 10.48577/jpl.dtusqw
title: Jupiter's Equatorial Plumes and Hot Spots: Spectral 2 Mapping from Gemini/TEXES and Juno/MWR

description: We present multi-wavelength measurements of the thermal, chemical, and cloud contrasts associated with the visibly dark formations (also known as 5-m hot spots) and intervening bright plumes on the boundary between Jupiter's Equatorial Zone (EZ) and North Equatorial Belt (NEB). Observations made by the TEXES 5-20 micron spectrometer at the Gemini North Telescope in March 2017 reveal the upper-tropospheric properties of 12 hot spots, which are directly compared to measurements by Juno using the Microwave Radiometer (MWR), JIRAM at 5 m, and JunoCam visible images. MWR and thermal-infrared spectroscopic results are consistent near 0.7 bar. Mid-infrared-derived aerosol opacity is consistent with that inferred from visible-albedo and 5-micron opacity maps. Aerosol contrasts, the defining characteristics of the cloudy plumes and aerosol-depleted hot spots, are not a good proxy for microwave brightness. The hot spots are neither uniformly warmer nor ammonia-depleted compared to their surroundings at p &lt; 1 bar. At 0.7 bar, the microwave brightness at the edges of hot spots is comparable to other features within the NEB. Conversely, hot spots are brighter at 1.5 bar, signifying either warm temperatures and/or depleted NH3 at depth. Temperatures and ammonia are spatially variable within the hot spots, so the precise location of the observations matters to their interpretation. Reflective plumes sometimes have enhanced NH3, cold temperatures, and elevated aerosol opacity, but each plume appears different. Neither plumes nor hot spots had microwave signatures in channels sensing p &gt; 10 bars, suggesting that the hot-spot/plume wave is a relatively shallow feature.
DOI: 10.48577/jpl.i9nwvt
title: Ice Giant Circulation Patterns: Implications for Atmospheric Probes

description: Atmospheric circulation patterns derived from multi-spectral remote sensing can serve as a guide for choosing a suitable entry location for a future in situ probe mission to the Ice Giants. Since the Voyager-2 flybys in the 1980s, three decades of observations from ground- and space-based observatories have generated a picture of Ice Giant circulation that is complex, perplexing, and altogether unlike that seen on the Gas Giants. This review seeks to reconcile the various competing circulation patterns from an observational perspective, accounting for spatially-resolved measurements of: zonal albedo contrasts and banded appearances; cloud-tracked zonal winds; temperature and para-H2 measurements above the condensate clouds; and equator-to-pole contrasts in condensable volatiles (methane, ammonia, and hydrogen sulphide) in the deeper troposphere. These observations identify three distinct latitude domains: an equatorial domain of deep upwelling and upper-tropospheric subsidence, potentially bounded by peaks in the retrograde zonal jet and analogous to Jovian cyclonic belts; a mid-latitude transitional domain of upper-tropospheric upwelling, vigorous cloud activity, analogous to Jovian anticyclonic zones; and a polar domain of strong subsidence, volatile depletion, and small-scale (and potentially seasonally-variable) convective activity. Taken together, the multi-wavelength observations suggest a tiered structure of stacked circulation cells (at least two in the troposphere and one in the stratosphere), potentially separated in the vertical by (i) strong molecular weight gradients associated with cloud condensation, and by (ii) transitions from a thermally-direct circulation regime at depth to a wave- and radiative-driven circulation regime at high altitude. The inferred circulation can be tested in the coming decade by 3D numerical simulations of the atmosphere, and by observations from future world-class facilities. The carrier spacecraft for any probe entry mission must ultimately carry a suite of remote-sensing instruments capable of fully constraining the atmospheric motions at the probe descent location.
DOI: 10.48577/jpl.f4agdi
title: Vertically-resolved observations of Jupiter’s quasi-quadrennial oscillation from 2012 to 2019

description: Over the last eight years, a rich dataset of mid-infrared CH4 observations from the TEXES instrument at IRTF has been used to characterize the thermal evolution of Jupiter’s stratosphere. These data were used to produce vertically-resolved temperature maps between latitudes of 50◦S and 50◦N, allowing us to track approximately two periods of Jupiter’s quasi-quadrennial oscillation (QQO). During the first five years of observations, the QQO has a smooth sinusoidal pattern with a period of 4.0 ± 0.2 years and an amplitude of 7 ± 1 K at 13.5 mbar (our region of maximum sensitivity). In 2017, we note an abrupt change to this pattern, with the phase being shifted backwards by ∼1 year. Searching for possible causes of this QQO delay, we investigated the TEXES zonally-resolved temperature retrievals and found that in May/June 2017, there was an unusually warm thermal anomaly located at a latitude of 28◦N and a pressure of 1.2 mbar, moving westward with a velocity of 19 ± 4 ms−1. We suggest that there may be a link between these two events.
DOI: 10.48577/jpl.mhjisv
title: Turbulence Power Spectra in Regions Surrounding Jupiter's South Polar Cyclones From Juno/JIRAM

description: We present a power spectral analysis of two narrow annular regions near Jupiter's South Pole derived from data acquired by the Jovian Infrared Auroral Mapper instrument onboard NASA's Juno mission. In particular, our analysis focuses on the data set acquired by the Jovian Infrared Auroral Mapper M‐band imager (hereafter IMG‐M) that probes Jupiter's thermal emission in a spectral window centered at 4.8 μm. We analyze the power spectral densities of circular paths outside and inside of cyclones on images acquired during six Juno perijoves. The typical spatial resolution is around 55 km pixel−1. We limited our analysis to six acquisitions of the South Pole from February 2017 to May 2018. The power spectral densities both outside and inside the circumpolar ring seem to follow two different power laws. The wave numbers follow average power laws of −0.9 ± 0.2 (inside) and −1.2 ± 0.2 (outside) and of −3.2 ± 0.3 (inside) and −3.4 ± 0.2 (outside), respectively, beneath and above the transition in slope located at ~2 × 10−3 km−1 wave number. This kind of spectral behavior is typical of two‐dimensional turbulence. We interpret the 500 km length scale, corresponding to the transition in slope, as the Rossby deformation radius. It is compatible with the dimensions of a subset of eddy features visible in the regions analyzed, suggesting that a baroclinic instability may exist. If so, it means that the quasi‐geostrophic approximation is valid in this context.
DOI: 10.48577/jpl.afz3af
title: Fluctuations in the reversal of Jupiter’s stratospheric jet streams

description: Solar System planetary atmospheres, from the terrestrial planets to the giants, display a banded structure of winds and temperatures over a wide range of altitudes. The equatorial stratospheres of the Earth, Jupiter, and Saturn all exhibit a remarkable periodic oscillation of their temperatures (and therefore winds) with height, forced by waves produced by tropospheric meteorology far below. Earth's Quasi-Biennial Oscillation (QBO, thought to be regular with a ~28-month average period) and Saturn's Quasi-Periodic Equatorial Oscillation (QPO, with a ~15-year period) have recently been observed to experience severe disruptions in their periodicities and vertical structure as a consequence of atmospheric events occurring far from the equator. During these extreme events, waves injected additional angular momentum into their stratospheres, altering the regular signals of the QBO on Earth and the QPO on Saturn. Using three decades of infrared observations of Jupiter, we reveal for the rst time that its QQO can also be perturbed by strong tropospheric activity at the equator and at higher latitudes. Observations of Jupiter's stratospheric temperatures between 1980 and 2011 show two significantly difierent periods of the QQO, with a 5.7-year period between 1980 and 1990 and 3.9 years between 1996 and 2006. A constant 4- 5-year period (reported by previous studies) over 1980-2011 fails to reproduce either the observed stratospheric temperature oscillations or the odd behavior after 2007. Following the observed periodicities, local temperature minima were expected to be observed at the equator in 1992 and 2007. However, observations reveal the complete opposite, suggesting major disruption to the predicted QQO pattern. Unlike Earth's QBO, Jupiter's stratospheric oscillation appeared to lock into a new period entirely after the 1992 disruption, something never previously observed on any terrestrial or giant planet. This anomalous behavior coincided with dramatic planetary-scale disturbances observed in 1990-1992 and 2006-2007 in the equatorial and low-latitudes troposphere, which completely altered Jupiter's banded cloud morphology. Unlike on Saturn, where the QPO disruption was due to waves propagating equatorwards from the enormous hot stratospheric vortex seated at 40 deg N, the Jovian disruption is connected to waves generated by equatorial and non-equatorial meteorological sources within the ammonia cloud deck, indicating that disruptions in equatorial oscillations are not simply limited to giant storms like those on Saturn. This interconnectivity between the troposphere and stratosphere on the archetypal gas giant, whereby distant meteorology can severely disrupt the regular oscillations at high altitudes, provides valuable constraints on numerical atmospheric simulations and opens up a new window into the shared dynamics of terrestrial and giant-planet atmospheres.
DOI: 10.48577/jpl.vagmdc
title: On the clouds and ammonia in Jupiter’s upper troposphere from Juno JIRAM reflectivity observations

description: We analyse spectra measured by the Jovian Infrared Auroral Mapper (JIRAM, a payload element of the NASA Juno mission) in the 3150-4910 cm-1 (2.0-3.2 μm) range during the perijiove passage of August 2016. Despite modelling uncertainties, the quality and the relative uniformity of the dataset allow us to determine several parameters characterizing the Jupiter’s upper troposphere in the latitude range 35°S-30°N. Ammonia relative humidity at 500 millibars varies between 5 per cent to supersaturation beyond 100 per cent for about 3 per cent of the processed spectra. Ammonia appears depleted over belts and relatively enhanced over zones. Local variations of ammonia, arguably associated with local dynamics, are found to occur in several locations on the planet (Oval BA, South Equatorial Belt). Cloud altitude, defined as the level where aerosol opacity reaches unit value at 3650 cm-1 (2.74 μm), is maximum over the Great Red Spot (&gt;20 km above the 1 bar level) and the zones (15 km) while it decreases over the belts and toward higher latitudes. The aerosol opacity scale height suggests more compact clouds over zones and more diffuse clouds over belts. The integrated opacity of clouds above the 1.3-bar pressure level is found to be minimum in regions where thermal emission of the deeper atmosphere is maximum. The opacity of tropospheric haze above the 200-mbar level also increases over zones. Our results are consistent with a Hadley-type circulation scheme previously proposed in literature for belts and zones, with clear hemisphere asymmetries in cloud and haze.
DOI: 10.48577/jpl.bex2az
title: Plasma Hollow Cathodes

description: Hollow cathode plasma discharges are a fundamental part of large variety of applications in industry, academia and space. From surface processing and coatings deposition to plasma-surface interactions research and electric propulsion, advances in hollow cathode modeling and performance are critically important to the progress and evolution of these and other technology areas. This paper describes perspectives on the progress has been made in recent years in the modeling and performance of hollow cathodes used in plasma discharges. While many of the developments have been driven by the demanding requirements of electric propulsion applications, the information provided applies to all thermionic hollow cathodes and their applications. In the paper we describe the status of 2-D global simulations of the hollow cathode plasmas, hollow cathode plume instabilities, the development of higher current cathodes and low current heaterless cathode technologies. Advances in the understanding and technology in these areas and some of the challenges that still need to be addressed and solved are discussed.This paper is an invited Perspective article.
DOI: 10.48577/jpl.gandga
title: The water abundance in Jupiter’s equatorial zone

description: Oxygen is the most common element after hydrogen and helium in Jupiter’s atmosphere, and may have been the primary condensable (as water ice) in the protoplanetary disk. Prior to the Juno mission, in situ measurements of Jupiter’s water abundance were obtained from the Galileo probe, which dropped into a meteorologically anomalous site. The findings of the Galileo probe were inconclusive because the concentration of water was still increasing when the probe ceased sending data. Here we report on the water abundance in the equatorial region (0 to 4 degrees north latitude), based on data taken at 1.25 to 22 GHz from the Juno microwave radiometer, probing pressures of approximately 0.7 to 30 bar. Because Juno discovered the deep atmosphere to be surprisingly variable as a function of latitude, it remains to confirm whether the equatorial abundance represents Jupiter’s global water abundance. The water abundance at the equatorial region is inferred to be 2:5 + 2:2 -1:6 x 10^3 ppm, or 2:7 + 2:4 -1:7I times the elemental ratio of protosolar oxygen to hydrogen (1σ uncertainties). If this reflects the global water abundance, the result suggests that the planetesimals that formed Jupiter were unlikely to have been water-rich clathrate hydrates.
DOI: 10.48577/jpl.pfaqzh
title: Jupiter’s Great Red Spot: Strong interactions with incoming anticyclones in 2019

description: Jupiter’s Great Red Spot (GRS), a giant anticyclone, is the largest and longest-lived of all the vortices observed in planetary atmospheres. During its history, the GRS has shrunk to half its size since 1879, and encountered many smaller anticyclones and other dynamical features that interacted in a complex way. In 2018-2020, while having a historically small size, its structure and even its survival appeared to be threatened when a series of anticyclones moving in from the east tore off large fragments of the red area and distorted its shape. In this work we report observations of the dynamics of these interactions and show that as a result the GRS increased its internal rotation velocity, maintaining its vorticity but decreasing its visible area, and suffering a transient change in its otherwise steady 90-day oscillation in longitude. From a radiative transfer analysis and numerical simulations of the dynamics we show that the interactions affected the upper cloud tops of the GRS. We argue that the intense vorticity of the GRS, together with its larger size and depth compared to the interacting vortices, guarantees its long lifetime.
DOI: 10.48577/jpl.5dtoub
title: New evidence for recent increase in global land evapotranspiration

description: Accurate quantification of global land evapotranspiration is necessary for understanding variability in the global water cycle, which is expected to intensify under climate change. Current global evapotranspiration products are derived from a variety of sources including models, remote sensing, and in situ observations. But existing approaches contain extensive uncertainties, for example relating to model structure or the upscaling of observations to a global level; as a result, variability and trends in global evapotranspiration remain unclear. Here we show that global land evapotranspiration has increased by 10±2% between 2003 to 2019, and that precipitation is increasingly partitioned into evapotranspiration rather than runoff. Our results are based on an independent water-balance ensemble time series of global land evapotranspiration with uncertainty distribution, using data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) satellites. Variability in global land evapotranspiration is positively correlated with the El Niño-Southern Oscillation. The main driver of the trend, however, is increasing land temperature. Our findings provide an observational constraint on land evapotranspiration, and are consistent with the hypothesis that global evapotranspiration should increase in a warming climate.