pinecone/core-2020-05-10-deduplication huggingface dataset:
Simultaneous conjugate observations of small-scale structures in Saturn's dayside ultraviolet auroras: Implications for physical origins

Small-scale features in Saturn's dayside UV auroras are examined using images obtained on 32 Hubble Space Telescope visits close to Saturn equinox when both northern and southern emissions were simultaneously observed, allowing their interhemispheric conjugacy to be investigated. Eastward-propagating patches in the dawn-to-noon sector were observed on ~70% of visits, which when present were nearly always observed both north and south. The patches were generally not closely conjugate, however, but typically displaced in local time by ~0.5–1 h, with maxima in one hemisphere falling near minima in the other. Averaged angular velocities were ~80% of rigid corotation, larger than plasma angular velocities reported in the outer magnetosphere to which the emissions are likely conjugate. We suggest the patches are associated with field-aligned currents of eastward-propagating ULF waves, specifically second harmonic Alfvén resonances with typical azimuthal wave numbers m ≈ 20 and plasma rest frame periods ~80 min, plausibly driven by drift-bounce resonance with hot magnetospheric water ions. Transient dusk sector emissions of ~10–30 min duration were also observed on ~40% of visits, and found to be strictly nonconjugate, with enhancements in one hemisphere, north or south, being unaccompanied by enhancements in the other. We suggest an association with open flux tubes, and discuss one scenario where hemispheric symmetry is broken on newly opened flux tubes via the interplanetary magnetic field Y component, plausibly consistent with nonconjugate events north and south, preferential postnoon occurrence, and time scales of a few tens of minutes, though the expected relationship with the Y component remains to be established.STFC. Grant Number: ST/H002480/1Peer-reviewedPublisher Versio
Near-lunar proton velocity distribution explained by electrostatic acceleration

The observation of parallel ion velocity in the near-lunar wake approximately equal to external solar wind velocity can be explained within uncertainties by an analytic electrostatic expansion model. The one-dimensional model frequently used is inadequate because it does not account for the moon's spherical shape. However, application of a more recent generalization to three dimensions of the solution along characteristics predicts higher velocities and is probably sufficient to account for the SARA observations on the Chandrayaan-1 spacecraft
Temporal and spatial dynamics of the regions 1 and 2 Birkeland currents during substorms

[1] We use current density data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to identify the location of maximum region 1 current at all magnetic local times (MLTs). We term this location the R1 oval. Comparing the R1 oval location with particle precipitation boundaries identified in DMSP data, we find that the R1 oval is located on average within 1° of particle signatures associated with the open/closed field line boundary (OCB) across dayside and nightside MLTs. We hence conclude that the R1 oval can be used as a proxy for the location of the OCB. Studying the amount of magnetic flux enclosed by the R1 oval during the substorm cycle, we find that the R1 oval flux is well organized by it: during the growth phase the R1 oval location moves equatorward as the amount of magnetic flux increases whereas after substorm expansion phase onset significant flux closure occurs as the R1 current location retreats to higher latitudes. For about 15 min after expansion phase onset, the amount of open magnetic flux continues to increase indicating that dayside reconnection dominates over nightside reconnection. In the current density data, we find evidence of the substorm current wedge and also show that the dayside R1 currents are stronger than their nightside counterpart during the substorm growth phase, whereas after expansion phase onset, the nightside R1 currents dominate. Our observations of the current distribution and OCB movement during the substorm cycle are in excellent agreement with the expanding/contracting polar cap paradigm.Peer-reviewedPublisher Versio
Long-term ionospheric cooling: Dependency on local time, season, solar activity, and geomagnetic activity

Ionospheric ion temperature Ti is an excellent approximation to neutral temperature Tn in the thermosphere, especially for altitudes below 300 km. This analysis of long‒term Ti trends in the F region over different local times is based on a database of incoherent scatter radar (ISR) observations spanning more than three solar cycles during 1968–2006 at Millstone Hill and represents an extended effort to a prior study focusing on noon‒time only. This study provides important information for understanding the difference between the ISR and other results. A gross average of the Ti trend at heights of Ti ∼ Tn (200–350 km) is ∼ −4 K/decade, a cooling trend close to the Tn estimation based on the satellite neutral density data. However, there exists considerable variability in the cooling: it is strong during the day and very weak during the night with a large apparent warming at low altitudes (200–350 km); it is strong at solar minimum for both daytime and nighttime. The strongest cooling for altitudes below 375 km occurs around 90–120 solar flux units of the 10.7 cm solar flux, not at the lowest solar flux. There appears more cooling toward high magnetic activity, but this dependency is very weak. No consistent and substantial seasonal dependency across different heights was found. We speculate that a fraction of the observed cooling trend may be contributed by a gradual shifting away from the sub‒auroral region at Millstone Hill, as part of the secular change in the Earth's magnetic field. In this 39 year long series of data record, two anomalous Ti drops were noticed, and we speculate on their connection to volcano eruptions in 1982 and 1991.National Science Foundation (U.S.) (Award AGS-1042569
On the influence of open magnetic flux on substorm intensity: Ground- and space-based observations

[1] Using the location of maximum region 1 current determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment as a proxy for the open/closed field line boundary, we monitor the evolution of the amount of open magnetic flux inside the magnetosphere during 772 substorms. We then divide all substorms into three classes, depending on the amount of open flux at expansion phase onset. Studying the temporal variations during the substorms of each class for a number of related geophysical parameters, we find that substorms occurring while the amount of open flux is large are generally more intense. By intense we mean that the auroral electrojet, region 1 current, auroral brightness, tail dipolarization and flow speed, ground magnetic signatures, Pi2 wave power, as well as the intensity and extent of the substorm current wedge (SCW) are all larger than during substorms that occur on a contracted polar cap. The SCW manifests itself as an intensification of the nightside R1 and R2 current system after onset. Our analysis shows that to dispose of large amounts of accumulated open magnetic flux, large substorms are triggered in the terrestrial magnetosphere.Peer-reviewedPublisher Versio
Statistical analysis of an ionospheric parameter as a base for earthquake prediction

International audience[1] This paper is related to the use of ionospheric density variations to tentatively predict earthquakes. The results of this statistical analysis are presented as a function of various parameters. The ion density was recorded by the low-altitude satellite DEMETER during more than 6 years, and a search for anomalies was automatically conducted with the complete data set. In a second time, a software checked if each anomaly could correspond to an earthquake. The search was conducted at less than 1500 km from the anomaly positions, and until 15 days after the anomaly time. The earthquakes have been classified depending on their magnitude, depth, and position (below the sea or inland). This attempt to predict earthquakes of course generates a lot of false alarms and wrong detections. Nevertheless, it is shown that the number of good detections increases with the magnitude of the earthquakes. In average the number of perturbations is higher the day of the earthquake, and then smoothly decreases for the days before. Earthquakes below the sea are better detected. There are seismic areas close to the South Atlantic Magnetic Anomaly and at high latitudes where the number of natural perturbations is too important to expect a high number of good detections. Finally, when there are several perturbations corresponding to a single earthquake, it is possible to combine their positions to have a better estimation of the location of the future epicenter. However, uncertainties about the time and the magnitude are large. Citation: Li, M., and M. Parrot (2013), Statistical analysis of an ionospheric parameter as a base for earthquake prediction
Dual periodicities in the flapping of Saturn's magnetodisk

In this report, we modify the model of Arridge et al. (2011) which was proposed to describe the shape of the magnetodisk of Saturn and its north-south oscillations near the planetary rotation period. The modification is based on the recent results of Provan et al. (2011, 2012) and Andrews et al. (2012), who have shown that the magnetic modulations near the current sheet exhibit dual periodicities, and derived magnetic phase functions for the northern and southern period modulations from the magnetic field data. Using a modified model in which the effects of both modulations are included, specifically related to the modulations of the radial component of the magnetic field, we show that the oscillations can be modeled without the use of an arbitrarily assigned oscillation phase value as employed in the previous work of Szego et al. (2012). In addition, the best fit amplitudes of the two oscillations are found to be nearly constant for a majority of the magnetodisk data analyzed, such that a single model with one fixed parameter fits well to the data for a majority of the passes.Work at Leicester was supported by STFC grant ST/H002480/1.Peer-reviewedPublisher Versio
Quasi-steady, marginally unstable electron cyclotron harmonic wave amplitudes

Electron cyclotron harmonic (ECH) waves have long been considered a potential driver of diffuse aurora in Earth's magnetotail. However, the scarcity of intense ECH emissions in the outer magnetotail suggests that our understanding of the amplification and the relative importance of these waves for electron scattering is lacking. We conduct a comprehensive study of wave growth and quasi-linear diffusion to estimate the amplitude of loss-cone-driven ECH waves once diffusion and growth balance but before convection or losses alter the background hot plasma sheet population. We expect this to be the most common state of the plasma sheet between episodes of fast convection. For any given wave amplitude, we model electron diffusion caused by interaction with ECH waves using a 2-D bounce-averaged Fokker-Planck equation. After fitting the resultant electron distributions as a superposition of multicomponent subtracted bi-Maxwellians, we estimate the maximum path-integrated gain using the HOTRAY ray-tracing code. We argue that the wave amplitude during quasi-steady state is the inflection point on a gain-amplitude curve. During quasi-steady state, ECH wave amplitudes can be significant (~1 mV/m) at L ~ 8 but drop to very low values (<~0.1 mV/m) in the outer magnetotail (L ~ 16) and likely fall below the sensitivity of typical instrumentation relatively close to Earth mainly because of the smallness of the loss cone. Our result reinforces the potentially important role of ECH waves in driving diffuse aurora and suggests that careful comparison of theoretical wave amplitude estimates and observations is required for resolving the equatorial scattering mechanism of diffuse auroral precipitation
Response of Uranus' auroras to solar wind compressions at equinox

We consider open flux production and magnetic tail formation for the unique physical circumstances at Uranus, where the planet's spin axis lies close to the orbit plane, while the magnetic dipole has a large ~60° inclination to the spin axis. Under these circumstances, open flux production and transport into the nightside can in principle occur continuously for near-solstice conditions, leading to the formation of a well-developed bipolar rotating magnetic tail, as observed during the Voyager 2 flyby in 1986. However, it is argued that tail formation will be significantly inhibited near to equinox, as open tubes are wound over the dayside magnetopause by planetary rotation, thus reducing further open flux production, and are compressed together north or south of the planet promoting “tail” reconnection and open flux closure. If so, this may account for the weak auroral responses to predicted solar wind compressions of Uranus' magnetosphere reported recently from Hubble Space Telescope observations under near-equinoctial conditions. Major auroral responses are observed following strong compressions at Earth and Saturn resulting from rapid and substantial closure of preexisting open flux in the tail. The lack of such a response at Uranus near equinox may thus reflect the lack of a well-developed tail under these conditions.This work was stimulated by observations\ud
made by the NASA/ESA Hubble Space Telescope (GO Program 12601).\ud
The work was\ud
supported by STFC grants ST/H002480/1 and ST/K001000/1.Peer-reviewedPublisher Versio
Neutron Monitor Yield Function: New Improved computations

A ground-based neutron monitor is a standard tool to measure cosmic ray
variability near Earth, and it is crucially important to know its yield
function for primary cosmic rays. Although there are several earlier
theoretically calculated yield functions, none of them agrees with experimental
data of latitude surveys of sea-level neutron monitors, thus suggesting for an
inconsistency. A newly computed yield function of the standard sea-level 6NM64
neutron monitor is presented here separately for primary cosmic ray protons and
$\alpha-$particles, the latter representing also heavier species of cosmic
rays. The computations have been done using the GEANT-4 Planetocosmics
Monte-Carlo tool and a realistic curved atmospheric model. For the first time,
an effect of the geometrical correction of the neutron monitor effective area,
related to the finite lateral expansion of the cosmic ray induced atmospheric
cascade, is considered, that was neglected in the previous studies. This
correction slightly enhances the relative impact of higher-energy cosmic rays
(energy above 5--10 GeV/nucleon) in neutron monitor count rate. The new
computation finally resolves the long-standing problem of disagreement between
the theoretically calculated spatial variability of cosmic rays over the globe
and experimental latitude surveys. The newly calculated yield function,
corrected for this geometrical factor, appears fully consistent with the
experimental latitude surveys of neutron monitors performed during three
consecutive solar minima in 1976--77, 1986--87 and 1996--97. Thus, we provide a
new yield function of the standard sea-level neutron monitor 6NM64 that is
validated against experimental data.Comment: Includes also Erratum (submitted to JGR) to Table
Energetic neutral atom imaging of the lunar surface

Since the Moon is not shielded by a global magnetic field or by an atmosphere, solar wind plasma impinges onto the lunar surface almost unhindered. Until recently, it was assumed that almost all of the impinging solar wind ions are absorbed by the surface. However, recent Interstellar Boundary Explorer, Chandrayaan-1, and Kaguya observations showed that the interaction process between the solar wind ions and the lunar surface is more complex than previously assumed. In contrast to previous assumptions, a large fraction of the impinging solar wind ions is backscattered as energetic neutral atoms. Using the complete Chandrayaan-1 Energetic Neutral Analyzer data set, we compute a global solar wind reflection ratio of 0.16 ± 0.05 from the lunar surface. Since these backscattered neutral particles are not affected by any electric or magnetic fields, each particle's point of origin on the lunar surface can be determined in a straight-forward manner allowing us to create energetic neutral atom maps of the lunar surface. The energetic neutral atom measurements recorded by the Chandrayaan-1 Energetic Neutral Analyzer cover ˜89% of the lunar surface, whereby the lunar farside is almost completely covered. We analyzed all available energetic neutral atom measurements recorded by the Chandrayaan-1 Energetic Neutral Analyzer to create the first global energetic neutral hydrogen maps of the lunar surface
CO Cameron band and CO2+ UV doublet emissions in the dayglow of Venus:
  Role of CO in the Cameron band production

Present study deals with the model calculations of CO Cameron band and CO2+
ultraviolet doublet emissions in the dayglow of Venus. The overhead and limb
intensities of CO Cameron band and CO2+ UV doublet emissions are calculated for
low, moderate, and high solar activity conditions. Using updated cross
sections, the impact of dierent e-CO cross section for Cameron band production
is estimated. The electron impact on CO is the major source mechanism of
Cameron band, followed by electron and photon impact dissociation of CO2. The
overhead intensities of CO Cameron band and CO2+ UV doublet emissions are about
a factor of 2 higher in solar maximum than those in solar minimum condition.
The effect of solar EUV flux models on the emission intensity is ~30-40% in
solar minimum condition and ~2-10% in solar maximum condition. At the altitude
of emission peak (135 km), the model predicted limb intensity of CO Cameron
band and CO2+ UV doublet emissions in moderate (F10.7 = 130) solar activity
condition is about 2400 and 300 kR, respectively, which is in agreement with
the very recently published SPICAV/Venus Express observation. The model limb
intensity profiles of CO Cameron band and CO2+ UV doublet are compared with
SPICAV observation. We also calculated intensities of N2 Vegard-Kaplan UV bands
and OI 2972 {\AA} emissions during moderate and high solar activity conditions.Comment: 12 pages, 10 figures. In Journal of Geophysical Research, 201
Longitudinal modulation of the brightness of Io's auroral footprint emission: Comparison with models

[1] The auroral emission close to the foot of Io's magnetic flux tube has been known for over a decade to be one of the key parameters characterizing the electrodynamic interaction between the satellite and Jupiter's magnetosphere. Ten years of observations of Io's magnetic footprint brightness have been conducted via far ultraviolet imaging by two instruments, the Space Telescope Imaging Spectrograph and the Advanced Camera for Surveys, on board the Hubble Space Telescope. The variation of Io's magnetic footprint brightness was found to have a strong correlation with the satellite's location in system III longitude. The persistent pattern of the variation of the brightness of the auroral emission at Io's magnetic footprint with longitude over 10 years of observations implies that the footprint emissions are primarily determined by processes other than temporal variations of the plasma torus. The changing location of Io in the plasma torus with longitude corresponds to changes in centrifugal latitude and to the plasma density in the vicinity of Io, likely affecting the electrodynamic interaction at the satellite. To test this, quantitative models of electron density and the generated power near Io are applied to simulate the observed footprint brightness variation pattern. We find, however, that the longitudinal variations in plasma conditions needed to produce changes in the electrodynamic interaction comparable to the observed modulation of the footprint emissions would require an unrealistically colder plasma torus than previously measured. We quantify the additional energy needed to produce the asymmetric emission peaks at 110° and 270° longitudes.Peer-reviewedPublisher Versio
Long-term changes in solar quiet (Sq) geomagnetic variations related to Earth's magnetic field secular variation

The daily amplitude of the solar quiet (Sq) magnetic variation of the horizontal intensity, H, of observatories at low and midlatitudes is analyzed, in search of significant long-term trends. These trends are expected based on secular variations of the Earth's magnetic field (B) and increasing concentrations of greenhouse gases which can affect Sq for instance through their effect on ionospheric conductivities and E-region electron concentration. The hourly horizontal geomagnetic field component, H, measured at Apia, Fredericksburg, Hermanus, Bangui, and Trivandrum was analyzed for the period 1960–2000. The solar activity effect was filtered out from the daily Sq amplitude of H, and then linear trends were calculated and compared to trend values obtained from the Coupled Magnetosphere-Ionosphere-Thermosphere model. Linear trends were calculated separately for periods of different secular trends in the magnetic field intensity, B. We found significant trends in experimental data for Apia, Fredericksburg, Hermanus, and for the period 1960–1983 for Bangui. There is reasonable quantitative agreement between experimental and simulated trends, and a qualitative agreement with trends expected from the secular trend in B
Modeling Birkeland currents in the expanding/contracting polar cap paradigm

[1] We present a simple mathematical model of the region 1 and 2 Birkeland current system intensities for differing dayside and nightside magnetic reconnection rates, consistent with the expanding/contracting polar cap paradigm of solar wind-magnetosphere-ionosphere coupling. The current intensities are shown to be dependent on the cross-polar cap potential, which is the average of the dayside and nightside reconnection rates. Current intensities are expected to maximize on the dayside or the nightside when magnetopause or magnetotail reconnection dominates. Current intensities are also dependent on the ionospheric conductance, the width of the merging gaps, the width of the ionospheric convection return flow region, and on the size of the polar cap.Peer-reviewedPublisher Versio