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See detailThe Effect of Foehn‐Induced Surface Melt on Firn Evolution Over the Northeast Antarctic Peninsula
Datta, R.T.; Tedesco, M.; Fettweis, Xavier ULiege et al

in Geophysical Research Letters (2019), 46

Surface meltwater ponding has been implicated as a major driver for recent ice shelf collapse as well as the speedup of tributary glaciers in the northeast Antarctic Peninsula. Surface melt on the NAP is ... [more ▼]

Surface meltwater ponding has been implicated as a major driver for recent ice shelf collapse as well as the speedup of tributary glaciers in the northeast Antarctic Peninsula. Surface melt on the NAP is impacted by the strength and frequency of westerly winds, which result in sporadic foehn flow. We estimate changes in the frequency of foehn flow and the associated impact on snow melt, density, and the percolation depth of meltwater over the period 1982–2017 using a regional climate model and passive microwave data. The first of two methods extracts spatial patterns of melt occurrence using empirical orthogonal function analysis. The second method applies the Foehn Index, introduced here to capture foehn occurrence over the full study domain. Both methods show substantial foehn‐induced melt late in the melt season since 2015, resulting in compounded densification of the near‐surface snow, with potential implications for future ice shelf stability. [less ▲]

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See detailAlfvén Wave Propagation in the Io Plasma Torus
Hinton, P. C.; Bagenal, F.; Bonfond, Bertrand ULiege

in Geophysical Research Letters (2019), 0(0),

Abstract Io, the most volcanically active body in the solar system, fuels a plasma torus around Jupiter with dissociation products of SO2 at a rate of ~1,000 kg/s. We use a combination of in situ Voyager ... [more ▼]

Abstract Io, the most volcanically active body in the solar system, fuels a plasma torus around Jupiter with dissociation products of SO2 at a rate of ~1,000 kg/s. We use a combination of in situ Voyager 1 data and Cassini Ultraviolet Imaging Spectrograph observations to constrain a diffusive equilibrium model of the Io plasma torus. The interaction of the Io plasma torus with Io launches Alfvén waves in both directions along magnetic field lines. We use the recent Juno-based JRM09 magnetic field model combined with our 3-D model of the Io plasma torus to simulate the propagation of Alfvén waves from the moon to the ionosphere of Jupiter. We map the location of multiple reflections of iogenic Alfvén waves between the northern and southern hemispheres. The location of the first few bounces of the Alfvén wave pattern match the Io auroral footprints observed by the Hubble Space Telescope. [less ▲]

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See detailWaves in Kinetic-Scale Magnetic Dips: MMS Observations in the Magnetosheath
Yao, S. T.; Shi, Q. Q.; Yao, Zhonghua ULiege et al

in Geophysical Research Letters (2019)

Kinetic-scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in ... [more ▼]

Kinetic-scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in recent observation and numerical simulation studies. These KSMDs likely play important roles in energy conversion and dissipation. In this study, we present observations of the KSMDs that are labeled whistler mode waves, electrostatic solitary waves, and electron cyclotron waves in the magnetosheath. The observations suggest that electron temperature anisotropy or beams within KSMD structures provide free energy to generate these waves. In addition, the occurrence rates of the waves are higher in the center of the magnetic dips than at their edges, implying that the KSMDs might be the origin of various kinds of waves. We suggest that the KSMDs could provide favorable conditions for the generation of waves and transfer energy to the waves in turbulent magnetosheath plasmas. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailEvolution of the Subauroral Polarization Stream Oscillations during the Severe Geomagnetic Storm on 20 November 2003
He, Fei; Zhang, Xiao-Xin; Wang, Wenbin et al

in Geophysical Research Letters (2019)

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See detailEvaluation of reconstructions of snow/ice melt in Greenland by regional atmospheric climate models using laser altimetry data
Sutterley, T.; Velicogna, I.; Fettweis, Xavier ULiege et al

in Geophysical Research Letters (2018), 45

he surface mass balance (SMB) of the Greenland Ice Sheet critically depend on the intensity of ice/snow melt in its ablation zone, but in‐situ data have been too limited to quantify the error of regional ... [more ▼]

he surface mass balance (SMB) of the Greenland Ice Sheet critically depend on the intensity of ice/snow melt in its ablation zone, but in‐situ data have been too limited to quantify the error of regional climate models. Here, we use 23 years of NASA satellite and airborne laser altimetry from the Airborne Topographic Mapper (ATM), Land, Vegetation and Ice Sensor (LVIS) and Ice, Cloud and land Elevation Satellite (ICESat) to generate time series of elevation change to compare with SMB products from the Regional Atmospheric Climate Model (RACMO2.3p2) and from the Modèle Atmosphérique Régional (MARv3.5.2). For 1994‐2016, the results agree at the 15‐26% level, with the largest discrepancy in north Greenland. During the cold summer 2015, the RMS discrepancy is 40% in the north, 30% in the southwest, and 18‐25% at low elevation. The difference drops to 23% in the southwest and 14% at low elevation during the 2016 warm summer. [less ▲]

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See detailImproving Greenland surface mass balance estimates through the assimilation of MODIS albedo: a case study along the K‐transect
Navari, M.; Margulis, S.; Tedesco, M. et al

in Geophysical Research Letters (2018)

Estimating the Greenland Ice Sheet (GrIS) surface mass balance (SMB) is an important component of current and future projections of sea level rise. Given the lack of in situ information, imperfect models ... [more ▼]

Estimating the Greenland Ice Sheet (GrIS) surface mass balance (SMB) is an important component of current and future projections of sea level rise. Given the lack of in situ information, imperfect models, and under‐utilized remote sensing data, it is critical to combine the available observations with a physically based model to better characterize the spatial and temporal variation of the GrIS SMB. This work proposes a data assimilation framework that yields SMB estimates that benefit from a state‐of‐the‐art snowpack model (Crocus) and a 16‐day albedo product. Comparison of our results against in‐situ SMB measurements from the Kangerlussuaq transect shows that assimilation of 16‐day albedo product reduces the root mean square error (RMSE) of the posterior estimates of SMB from 1240 millimeter water equivalent (mmWE/yr) to 230 mmWE/yr and reduces the bias from 1140 mmWE/yr to ‐20 mmWE/yr [less ▲]

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See detailHeliospheric conditions at Saturn during Cassini's Ring-Grazing and Proximal Orbits
Roussos, E.; Krupp, N.; Paranicas, C. et al

in Geophysical Research Letters (2018), 45

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See detailMMS observations of electron scale magnetic peak
Yao, S. T.; Shi, Q. Q.; Guo, R. L. et al

in Geophysical Research Letters (2018)

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See detailObservations of the Proton Aurora on Mars With SPICAM on Board Mars Express
Ritter, Birgit ULiege; Gérard, Jean-Claude ULiege; Hubert, Benoît ULiege et al

in Geophysical Research Letters (2018), 45

We report observations of the proton aurora at Mars, obtained with the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph on board Mars ... [more ▼]

We report observations of the proton aurora at Mars, obtained with the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph on board Mars Express between 2004 and 2011. This is a third type of UV aurora that is discovered on Mars, in addition to the discrete and diffuse nightside aurora. It is observed only on the dayside as it is produced by the direct interaction of solar wind protons with the upper atmosphere. The auroral signature is an enhancement of the Lyman-α emission in the order of a few kilorayleighs. The proton aurora features peak emissions around 120 to 150 km. From the full SPICAM database, limb observations have been investigated and six clear cases have been found. We identify either coronal mass ejections and/or corotating interaction regions as triggers for each of these events. [less ▲]

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See detail"Bar Code" Events in the Juno-UVS Data: A Signature ~10 MeV Electron Microbursts at Jupiter
Bonfond, Bertrand ULiege; Gladstone, G. R.; Grodent, Denis ULiege et al

in Geophysical Research Letters (2018), 0(ja),

One of the most intriguing discoveries of Juno is the quasi-systematic detection of up-going electrons above the auroral regions. Here we discuss a byproduct of the most energetic component of this ... [more ▼]

One of the most intriguing discoveries of Juno is the quasi-systematic detection of up-going electrons above the auroral regions. Here we discuss a byproduct of the most energetic component of this population: a contamination resembling bar codes in the Juno-UVS images. This pattern is likely caused by bursts of >10 MeV electrons penetrating the instrument. These events are mostly detected when Juno's magnetic footprint is located poleward of the main emission relative to the magnetic pole. The signal is not periodic, but the bursts are typically 0.1-1 second apart. They are essentially detected when Juno-UVS is oriented towards Jupiter, indicating that the signal is due to up-going electrons. The event detections occur between 1 and 7 Jovian radii above the 1 bar level, suggesting that the electron acceleration takes place close to Jupiter and is thus both strong and brief. [less ▲]

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See detailSaturn's northern aurorae at solstice from HST observations coordinated with Cassini's Grand Finale
Lamy, L.; Prangé, R.; Tao, C. et al

in Geophysical Research Letters (2018)

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See detailMagnetospheric Multiscale observations of electron scale magnetic peak
Yao, S. T.; Shi, Q. Q.; Guo, R. L. et al

in Geophysical Research Letters (2018), 45(2), 527-537

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See detailDiverse electron and ion acceleration characteristics observed over Jupiter's main aurora
Mauk, B. H.; Haggerty, D. K.; Paranicas, C. P. et al

in Geophysical Research Letters (2018)

Two new Juno-observed particle features of Jupiter's main aurora demonstrate substantial diversity of processes generating Jupiter's mysterious auroral emissions. It was previously speculated that ... [more ▼]

Two new Juno-observed particle features of Jupiter's main aurora demonstrate substantial diversity of processes generating Jupiter's mysterious auroral emissions. It was previously speculated that sometimes-observed potential-driven aurora (up to 400 kV) can turn into broadband stochastic acceleration (dominating at Jupiter) by means of instability. Here direct evidence for such a process is revealed with a “mono-energetic” electron inverted-V rising in energy to 200 keV, transforming into a region of broadband acceleration with downward energy fluxes tripling to 3000 mW/m2, and then transforming back into a mono-energetic structure ramping down from 200 keV. But a second feature of interest observed nearby is unlikely to have operated in the same way. Here a downward accelerated proton inverted-V, with inferred potentials to 300-400 kV, occurred simultaneously with downward accelerated broadband electrons with downward energy fluxes as high as any observed (~3000 mW/m2). This latter feature has no known precedent with Earth auroral observations. [less ▲]

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See detailAuroral storm and polar arcs at Saturn - Final Cassini/UVIS auroral observations
Palmaerts, Benjamin ULiege; Radioti, Aikaterini ULiege; Grodent, Denis ULiege et al

in Geophysical Research Letters (2018)

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph on board ... [more ▼]

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph on board Cassini observed Saturn's northern aurora for about 14 h. During these observations, several auroral structures appeared, providing clues about processes simultaneously occurring in Saturn's magnetosphere. The observed dawn auroral enhancement together with the magnetic eld and plasma wave data suggest that an intense flux closure process took place in the magnetotail. This enhanced magnetotail reconnection is likely caused by a magnetospheric compression induced by an interplanetary shock. Additionally, a polar arc is observed on the duskside, tracked for the rst time from its growth until its quasi-disappearance, and used as an indicator of reconnection location on the dayside magnetopause. Observation of an atypical auroral arc at very high latitudes supports the interplanetary shock scenario. [less ▲]

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See detailMorphology of the UV aurorae Jupiter during Juno’s first perijove observations
Bonfond, Bertrand ULiege; Gladstone, G. R.; Grodent, Denis ULiege et al

in Geophysical Research Letters (2017)

On 27 August 2016, the NASA Juno spacecraft performed its first close-up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno-ultraviolet ... [more ▼]

On 27 August 2016, the NASA Juno spacecraft performed its first close-up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno-ultraviolet spectrometer UV imaging spectrograph acquired at that time. Data were acquired during four sequences (three in the north, one in the south) from 5:00 UT to 13:00 UT. From these observations, we produced complete maps of the Jovian aurorae, including the nightside. The sequence shows the development of intense outer emission outside the main oval, first in a localized region (255 ∘ –295 ∘ System III longitude) and then all around the pole, followed by a large nightside protrusion of auroral emissions from the main emission into the polar region. Some localized features show signs of differential drift with energy, typical of plasma injections in the middle magnetosphere. Finally, the color-ratio map in the north shows a well-defined area in the polar region possibly linked to the polar cap. [less ▲]

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See detailTransient brightening of Jupiter’s aurora observed by the Hisaki satellite and Hubble Space Telescope during approach phase of the Juno spacecraft
Kimura, Tomoki; Nichols, J.D.; Gray, R.L. et al

in Geophysical Research Letters (2017), 44

In early 2014, continuous monitoring with the Hisaki satellite discovered transient auroral emission at Jupiter during a period when the solar wind was relatively quiet for a few days. Simultaneous ... [more ▼]

In early 2014, continuous monitoring with the Hisaki satellite discovered transient auroral emission at Jupiter during a period when the solar wind was relatively quiet for a few days. Simultaneous imaging made by the Hubble Space Telescope (HST) suggested that the transient aurora is associated with a global magnetospheric disturbance that spans from the inner to outer magnetosphere. However, the temporal and spatial evolutions of the magnetospheric disturbance were not resolved because of the lack of continuous monitoring of the transient aurora simultaneously with the imaging. Here we report the coordinated observation of the aurora and plasma torus made by Hisaki and HST during the approach phase of the Juno spacecraft in mid‐2016. On day 142, Hisaki detected a transient aurora with a maximum total H2 emission power of ~8.5 TW. The simultaneous HST imaging was indicative of a large “dawn storm,” which is associated with tail reconnection, at the onset of the transient aurora. The outer emission, which is associated with hot plasma injection in the inner magnetosphere, followed the dawn storm within less than two Jupiter rotations. The monitoring of the torus with Hisaki indicated that the hot plasma population increased in the torus during the transient aurora. These results imply that the magnetospheric disturbance is initiated via the tail reconnection and rapidly expands toward the inner magnetosphere, followed by the hot plasma injection reaching the plasma torus. This corresponds to the radially inward transport of the plasma and/or energy from the outer to the inner magnetosphere. [less ▲]

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See detailMartian mesospheric cloud observations by IUVS on MAVEN: Thermal tides coupled to the upper atmosphere
Stevens; Siskind; Evans et al

in Geophysical Research Letters (2017), 44

The manuscript describes the observation of Martian mesosphericclouds between 60 and 80 km altitude by the Imaging Ultraviolet Spectrograph (IUVS) on NASA’sMAVEN spacecraft. The cloud observations are ... [more ▼]

The manuscript describes the observation of Martian mesosphericclouds between 60 and 80 km altitude by the Imaging Ultraviolet Spectrograph (IUVS) on NASA’sMAVEN spacecraft. The cloud observations are uniquely obtained at early morning local times, whichcomplement previous observations obtained primarily later in the diurnal cycle. Differences in thegeographic distribution of the clouds from IUVS observations indicate that the local time is crucial for theinterpretation of mesospheric cloud formation. We also report concurrent observations of upperatmospheric scale heights near 170 km altitude, which are diagnostic of temperature. These observationssuggest that the dynamics enabling the formation of mesospheric clouds propagate all the way to theupper atmosphere. [less ▲]

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See detailPreliminary JIRAM results from Juno polar observations: 3. Evidence of diffuse methane presence in the Jupiter auroral regions
Moriconi, M. L.; Adriani, A.; Dinelli, B. M. et al

in Geophysical Research Letters (2017), 44(10), 4641-4648

Throughout the first orbit of the NASA Juno mission around Jupiter, the Jupiter InfraRed Auroral Mapper (JIRAM) targeted the northern and southern polar regions several times. The analyses of the acquired ... [more ▼]

Throughout the first orbit of the NASA Juno mission around Jupiter, the Jupiter InfraRed Auroral Mapper (JIRAM) targeted the northern and southern polar regions several times. The analyses of the acquired images and spectra confirmed a significant presence of methane (CH4) near both poles through its 3.3 μm emission overlapping the H3 + auroral feature at 3.31 μm. Neither acetylene (C2H2) nor ethane (C2H6) have been observed so far. The analysis method, developed for the retrieval of H3 + temperature and abundances and applied to the JIRAM-measured spectra, has enabled an estimate of the effective temperature for methane peak emission and the distribution of its spectral contribution in the polar regions. The enhanced methane inside the auroral oval regions in the two hemispheres at different longitude suggests an excitation mechanism driven by energized particle precipitation from the magnetosphere. ©2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailInfrared observations of Jovian aurora from Juno's first orbits: Main oval and satellite footprints
Mura, A.; Adriani, A.; Altieri, F. et al

in Geophysical Research Letters (2017), 44(11), 5308-5316

The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAM's imager channel observations of the H3 ... [more ▼]

The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. The first results of JIRAM's imager channel observations of the H3 + infrared emission, collected around the first Juno perijove, provide excellent spatial and temporal distribution of the Jovian aurorae, and show the morphology of the main ovals, the polar regions, and the footprints of Io, Europa and Ganymede. The extended Io “tail” persists for ~3 h after the passage of the satellite flux tube. Multi-arc structures of varied spatial extent appear in both main auroral ovals. Inside the main ovals, intense, localized emissions are observed. In the southern aurora, an evident circular region of strong depletion of H3 + emissions is partially surrounded by an intense emission arc. The southern aurora is brighter than the north one in these observations. Similar, probably conjugate emission patterns are distinguishable in both polar regions. ©2017. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailThe recent warming trend in North Greenland
Orsi, A.; Kawamura, K.; Masson-Delmotte, V. et al

in Geophysical Research Letters (2017)

The Arctic is among the fastest warming regions on Earth, but it is also one with limited spatial coverage of multi-decadal instrumental surface air temperature measurements. Consequently, atmospheric ... [more ▼]

The Arctic is among the fastest warming regions on Earth, but it is also one with limited spatial coverage of multi-decadal instrumental surface air temperature measurements. Consequently, atmospheric reanalyses are relatively unconstrained in this region, resulting in a large spread of estimated 30-year recent warming trends, which limits their use to investigate the mechanisms responsible for this trend. Here, we present a surface temperature reconstruction over 1982-2011 at NEEM (51∘ W, 77∘ N), in North Greenland, based on the inversion of borehole temperature and inert gas isotope data. We find that NEEM has warmed by 2.7±0.33∘C over the past 30 years, from the long-term 1900-1970 average of -28.55±0.29∘C. The warming trend is principally caused by an increase in downward longwave heat flux. Atmospheric reanalyses underestimate this trend by 17%, underlining the need for more in situ observations to validate reanalyses. [less ▲]

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