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Lake ice thickness (LIT) and lake water level (LWL) are two thematic products of lakes as an Essential Climate Variable (ECV). Lake water levels are routinely estimated using radar measurements from satellite altimetry missions, but the retrieval of LIT from such missions is relatively new. While there is growing interest in the production of climate data records of LIT through the processing of historical time series, there is a need to examine the impact of varying ice and overlying snow properties on radar altimetry and microwave radiometry measurements through full ice seasons. There is also recent realization that the presence of ice cover on lakes has an impact on the quality of LWL estimates for several weeks/months of the year. Thin ice during initial ice formation, the absence of snow on the ice surface, the presence of deformation features (i.e. cracks in the ice and pressure ridges), and snow/ice melt onset introduce uncertainty in the retrieval of LIT and LWL from state-of-the-art algorithms.This talk will present results from a study that examined the sensitivity of radar backscatter and microwave brightness temperature measurements from satellite altimetry missions to varying snow and ice properties on large northern lakes. The presentation will cover results from: 1) forward modelling experiments of brightness temperature (18-37 GHz) and backscatter/waveforms (3-36 GHz) using the Snow Microwave Radiative Transfer (SMRT) model linked to a thermodynamic lake ice model; and 2) the comparison of forward simulations of radar backscatter and brightness temperature with measurements from Sentinel-3 and Jason-3 missions., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The wide range of wind regimes in Antarctica interacts with the snow surface topography and shapes various snow bedforms, such as linear dunes or barchans. They are representative of the local scale processes of accumulation and erosion, and thus adapt to the change in snow structure, metamorphism, snow precipitation, and redistribution. Understanding these interactions is important to better constrain the surface mass balance, interpretation of ice core, and modelling of the near-surface wind field in Antarctica. While the wide variety of snow bedforms encountered at the Antarctic surface have been qualitatively described, little is known about their spatial distribution.In this study, we present a continent-wide study of linear dunes orientation in Antarctica in relation to wind regimes. We used Sentinel-2 and Landsat-8 images with, respectively, a 10 m and 15 m resolution to retrieve dune orientation. Using wind direction and speed from ERA5 Reanalysis with a 0.25°x0.25° resolution, we show that longitudinal dune is the predominant type of dune in Antarctica and that they form by elongation in the mean snow flux direction., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Sea ice thickness is essential for climate studies and numerical weather prediction. Radar altimetry has provided sea ice thickness measurement since the launch of ERS-1 and currently through CryoSat-2, but uncertainty arises from interactions between the emitted signal and snow cover on the ice surface. Snow and ice have been shown to affect the altimeter waveform mainly due to their microstructure properties, surface roughness and salinity. Therefore, modelling the scattering of the electromagnetic waves with the snowpack and ice is necessary to retrieve the sea ice thickness accurately. The Snow Microwave Radiative Transfer (SMRT) model can be used to simulate both snow cover and ice with salinity, which makes it suitable for modelling the altimeter waveform echo from the snow-covered sea ice. This work focuses on measurements made as part of the Altimetric Ku-band Radar Observations Simulated with SMRT (AKROSS) project. The AKROSS project was designed to provide the first evaluation of the SMRT model in altimeter mode for snow on sea ice. The purpose of this presentation is to evaluate SMRT in altimeter mode over sea ice by 1) evaluating the overall fit of the waveform with observations of CryoSat-2, 2) investigating the sensitivity of the Ku/Ka band for the CRISTAL mission of the European Space Agency (ESA)., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

International audience; To fully decipher the role of nitrate photolysis on the atmospheric oxidative capacity in snow-covered regions, NOx flux must be determined with more precision than existing estimates. Here, we introduce a method based on dynamic flux chamber measurements for evaluating the NOx production by photolysis of snowpack nitrate in Antarctica. Flux chamber experiments were conducted for the first time in Antarctica, at the French-Italian station Concordia, Dome C (75°06'S, 123°20’E, 3233 m a.s.l) during the 2019–2020 summer campaign. Measurements were gathered with several snow samples of different ages ranging from newly formed drifted snow to 6-year-old firn. Contrary to existing literature expectations, the daily average photolysis rate coefficient, urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0007, did not significantly vary between differently aged snow samples, suggesting that the photolabile nitrate in snow behaves as a single-family source with common photochemical properties, where a urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0008 = (2.37 urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0009 0.35) × 10−8 s−1 (1urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0011) has been calculated from December 10th 2019 to January 7th 2020. At Dome C summer daily average NOx flux, urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0015, based on measured NOx production rates was estimated to be (4.3 urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0017 1.2) × 108 molecules cm−2 s−1, which is 1.5–7 times less than the net NOx flux observed previously above snow at Dome C using the gradient flux method. Using these results, we extrapolated an annual continental snow sourced NOx budget of 0.017 urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0022 0.003 Tgurn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0023N y−1, urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-00252 times the nitrogen budget, (N-budget), of the stratospheric denitrification previously estimated for Antarctica. These quantifications of nitrate photolysis using flux chamber experiments provide a road-map toward a new parameterization of the urn:x-wiley:2169897X:media:jgrd57323:jgrd57323-math-0026 product that can improve future global and regional models of atmospheric chemistry.