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Author |
Alison F. Banwell, Rajashree Tri Datta, Rebecca L. Dell, Mahsa Moussavi, Ludovic Brucker, Ghislain Picard, Christopher A. Shuman, Laura A. Stevens |
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Title |
The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula |
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Journal |
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Year |
2021 |
Publication |
The Cryosphere |
Abbreviated Journal |
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Volume |
15 |
Issue |
2 |
Pages |
909-925 |
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Abstract |
In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of distinctly lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer and scatterometer data, which are sensitive to meltwater on the ice shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (2013 to 2020) and Sentinel-2 (2017 to 2020), record volumes of surface meltwater ponding were also observed on the northern GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of ponded meltwater on 19 January. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ?0 ?C for anomalously long periods (55 to 90 h) from late November onwards, which limited meltwater refreezing. The sustained warm periods were likely driven by warm, low-speed (?7.5 m s?1) northwesterly and northeasterly winds and not by foehn wind conditions, which were only present for 9 h total in the 2019/2020 melt season. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting. |
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1994-0416 |
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yes |
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Serial |
7654 |
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Author |
R. Olmi, M. Bittelli, G. Picard, L. Arnaud, A. Mialon, S. Priori |
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Title |
Investigating the influence of the grain size and distribution on the macroscopic dielectric properties of Antarctic firn |
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Year |
2021 |
Publication |
Cold Regions Science and Technology |
Abbreviated Journal |
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Volume |
185 |
Issue |
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Pages |
103254 |
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Keywords |
Antarctica Close?off Dielectric measurements Dielectric model Firn Full wave EM simulations Ice cores |
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1110 |
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0165-232X |
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yes |
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7995 |
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Title |
Radar altimeter waveform simulations in Antarctica with the Snow Microwave Radiative Transfer Model (SMRT) |
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Year |
2021 |
Publication |
Remote Sensing of Environment |
Abbreviated Journal |
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Volume |
263 |
Issue |
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Pages |
112534 |
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Keywords |
Antarctic ice sheet Field measurements Modeling Radar altimetry Remote sensing SMRT Waveform |
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Abstract |
Radar altimeters are important tools to monitor the volume of the ice sheets. The penetration of radar waves in the snowpack is a major source of uncertainty to retrieve surface elevation. To correct this effect, a better understanding of the sensitivity of the radar waveforms to snow properties is needed. Here, we present an extension of the Snow Model Radiative Transfer (SMRT) to compute radar waveforms and conduct a series of simulations on the Antarctic ice sheet. SMRT is driven by snow and surface roughness properties measured over a large latitudinal range during two field campaigns on the Antarctic Plateau. These measurements show that the snowpack is rougher, denser, less stratified, warmer, and has smaller snow grains near the coast than on the central Plateau. These simulations are compared to satellite observations in the Ka, Ku, and S bands. SMRT reproduces the observed waveforms well. For all sites and all sensors, the main contribution comes from the surface echo. The echo from snow grains (volume scattering) represents up to 40% of the amplitude of the total waveform power in the Ka band, and less at the lower frequencies. The highest amplitude is observed on the central Plateau due to the combination of higher reflection from the surface, higher scattering by snow grains in the Ka and Ku bands, and higher inter-layer reflections in the S band. In the Ka band, the wave penetrates in the snowpack less deeply on the central Plateau than near the coast because of the strong scattering caused by the larger snow grains. The opposite is observed in the S band, the wave penetrates deeper on the central Plateau because of the lower absorption due to the lower snow temperatures. The elevation bias caused by wave penetration into the snowpack show a constant bias of 10 cm for all sites in the Ka band, and a bias of 11 cm, and 21 cm in the Ku band for sites close to the coast and the central Plateau, respectively. Now that SMRT is performing waveform simulations, further work will address how the snowpack properties affect the parameters retrieved by more advanced retracking algorithms such as ICE-2 for different snow cover surfaces. |
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1110 |
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ISSN |
0034-4257 |
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yes |
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Serial |
7997 |
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Author |
Alexander Kokhanovsky, Simon Gascoin, Laurent Arnaud, Ghislain Picard |
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Title |
Retrieval of Snow Albedo and Total Ozone Column from Single-View MSI/S-2 Spectral Reflectance Measurements over Antarctica |
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Journal |
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Year |
2021 |
Publication |
Remote Sensing |
Abbreviated Journal |
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Volume |
13 |
Issue |
21 |
Pages |
4404 |
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Keywords |
albedo inverse problems light scattering radiative transfer snow snow grain size |
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1110 |
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2072-4292 |
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yes |
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Call Number |
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Serial |
8305 |
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Title |
Water Isotopic Signature of Surface Snow Metamorphism in Antarctica |
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Journal |
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Year |
2021 |
Publication |
Geophysical Research Letters |
Abbreviated Journal |
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Volume |
48 |
Issue |
17 |
Pages |
e2021GL093382 |
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Keywords |
excess Ice cores metamorhism Paleoclimate water isotopes |
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Abstract |
Water isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic composition. Using excess parameters (combining D,17O, and 18O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation. |
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1110 |
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ISSN |
1944-8007 |
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yes |
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8306 |
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Title |
A dedicated robust instrument for water vapor generation at low humidity for use with a laser water isotope analyzer in cold and dry polar regions |
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Journal |
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Year |
2021 |
Publication |
Atmospheric Measurement Techniques |
Abbreviated Journal |
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Volume |
14 |
Issue |
4 |
Pages |
2907-2918 |
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Programme |
1110,1169,1205 |
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Bachelor's thesis |
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ISSN |
1867-1381 |
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yes |
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Call Number |
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Serial |
8010 |
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Author |
G. Hubert, S. Aubry |
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Title |
Study of the Impact of Past Extreme Solar Events on the Modern Air Traffic |
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Journal |
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Year |
2021 |
Publication |
Space Weather |
Abbreviated Journal |
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Volume |
19 |
Issue |
4 |
Pages |
e2020SW002665 |
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Abstract |
The ancient solar energetic particle (SEP) events of 774/775 CE and 993/994 CE were characterized thanks to radionuclide productions stored in environmental archives as ice cores or tree rings. Primary cosmic ray spectra deduced from these cosmogenic isotope data indicate that the impact of these extreme SEP events would have been much more significant than any of the ones observed during the modern era. However, the impact of these should be studied more accurately in the framework of the ambient dose equivalent impacting aircrew and passengers in the air traffic context by considering physical parameters such as time profile or anisotropy properties. In this study, the impact that 774/775 CE and 993/994 CE past extreme SEP events could have had on modern air traffic is discussed. Possible event spectra for these ancient events are derived from the spectra ground-level enhancement (GLE) 5 and GLE 69, which have been observed during the modern era and have been widely studied/characterized using measurements. The investigations include the impact of the SEP activity on ambient dose equivalent, including detailed analyses considering route, airplane characteristics (departure, arrival, continent, airplane type), and the time occurrence of the SEP event. Statistical analyses show that additional dose levels can reach values on the order of 70 mSv, which is absolutely significant considering the current air traffic recommendations. The orders of magnitude of the ambient dose equivalent induced during past extreme SEP events raises a number of issues, both for aircrews and for avionics hardware. This study demonstrates that simulations can be useful for the evaluation of risks in case of extreme SEP events. |
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1112 |
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ISSN |
1542-7390 |
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yes |
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Call Number |
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Serial |
7934 |
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Author |
G. Hubert, S. Aubry |
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Title |
Simulation of atmospheric cosmic-rays and their impacts based on pre-calculated databases, physical models and computational methods |
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Year |
2021 |
Publication |
Journal of Computational Science |
Abbreviated Journal |
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Volume |
51 |
Issue |
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Pages |
101307 |
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Keywords |
Ambient dose equivalent Atmospheric cosmic-rays Cosmogenic nuclide production Multi-physics Single event effect |
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Abstract |
The atmospheric cosmic-ray environment is composed of secondary particles produced when primary cosmic rays interact with the nucleus of atmospheric atoms. Modeling of atmospheric radiations is essential for investigating their impacts on human activities such as radiation risks in aviation or scientific fields such as cosmogenic dating. The nuclear transport codes are a common and accurate way to model the cosmic ray interaction in the atmosphere with minimal approximations. However, tracking all produced secondary particles in each event in the whole depth of the atmosphere and sampling many events to obtain the statistically meaningful results would be a computational challenge and disadvantageous from the point of view of time consumption. This paper presents a computational platform names ATMOS CORE based on pre-calculated databases coupled to physical models and computational methods. The fields of application concern the atmospheric cosmic-rays characterization as well as their effects on electronics systems, on the ambient dose for aircrews or the cosmogenic nuclide production for dating activities. Some comparisons between simulations and measurements are also presented and discussed. |
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1112 |
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ISSN |
1877-7503 |
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yes |
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Call Number |
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Serial |
7957 |
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Author |
Guillaume Hubert |
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Title |
Analyses of the Secondary Cosmic Ray using CCD camera in high-altitude observatories and Antarctica stations |
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Peer-reviewed symposium |
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Year |
2021 |
Publication |
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Abbreviated Journal |
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Volume |
395 |
Issue |
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Pages |
1238 |
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Keywords |
Array Pixel Sensors (APS) Charge-Coupled Device (CCD) |
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Abstract |
Charge-Coupled Device (CCD) and Array Pixel Sensors (APS) can be used to image radiation-induced energy deposition. The high sensitivity of depleted silicon to ionizing radiation constitutes an opportunity to investigate radiation effects while it is a nuisance to astronomer activities. CCD and APS provide a better combination of spatial and intensity resolution for radiation events than other available types of detector. This paper proposes to analyze radiation events observed in the CCD camera and more specifically analyses of charge deposition spectra and spatially extensive events. Measurements were performed in the Pic du Midi from 2011 to 2015 and in the Concordia Antarctica station since 2018. Coupled transport models (i.e. particle transport and charge transport in semiconductors) allow investigating contributions to charge collection spectra as a function of the particle nature, i.e. neutron, proton and muon. Coupled measurements and simulations allow to access to the detected secondary CR flux and the charge deposition pattern. Results showed that high charge level events seen on atmospheric sites can be considered as hadronic component (mainly neutrons and protons) while low charge levels and punctual events are induced by muons which are able to generate up to 3 fC in the CCD camera. Hence, thanks to double level of measurement sites, muon discrimination from other secondary particles has been investigated. Cross-comparison analyses based on CCD and neutron spectrometers operated in both station/observatory investigate secondary CR dynamic. |
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1112 |
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yes |
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Call Number |
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Serial |
8325 |
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Author |
Guillaume Hubert |
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Title |
Continuously Measurements of Energy Spectra of Cosmic-Ray-induced-neutrons on the Concordia Antarctic Station for the period 2015-2021 |
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Year |
2021 |
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Abbreviated Journal |
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Volume |
395 |
Issue |
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Pages |
1263 |
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Abstract |
The CHINSTRAP (Continuous High-altitude Investigation of the Neutron Spectra for Terrestrial Radiation Antarctic Project) supported by the French Polar Agency (IPEV) aims at recording cosmic-ray (CR) induced-neutron spectra at the Concordia station since December 2015. The neutron spectrometer measures the neutron spectrum over a wide energy range from meV up to tens of GeV with a short time resolution. Several parameters can influence the measurement, including systematic and environmental effects such as the atmospheric pressure, the hydrometric environment close to the instrument and the atmospheric water vapor. This paper presents CR induced neutrons measurements analyses from 2015 to 2021 in Concordia, integrating corrections to take into account environmental and systematic effects. Long-term and short-term analyses are proposed, applied to count rate, fluxes and spectra. A last part investigates the contribution of modelling to data analyses and the ability to deduce the solar modulation from neutron spectra and the radiation field extrapolation using nuclear transport in atmosphere. An underlying objective is also to improve physical models allowing analyses of continuous and simultaneously measurements of CR induced neutrons spectra. |
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1112 |
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yes |
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Call Number |
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Serial |
8516 |
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