Snow transport favors strong sublimation and may therefore have an important effect on the surface mass balance of polar and high-mountain regions. Recently, small-scale models such as large-eddy simulation (LES) with Lagrangian snow particles have improved the understanding of snow transport processes and revealed shortcomings in the parameterizations of large-scale models. This study leverages LES simulations to assess and improve current parameterizations of sublimation and snow transport. Measurements from the S17 site, East Antarctica, are used to define realistic model parameters and boundary conditions and verify the plausibility of the simulations. Various parameterization options are tested in a simple one-dimensional model inspired by the large-scale model CRYOWRF. When parameterizing the moisture and heat fluxes for given mass and number mixing ratios of particles, four improvements lead to a good agreement with the LES simulations: (a) A low surface friction velocity, (b) at least one grid level in the saltation layer, (c) prognostic humidity and temperature values at all heights, and (d) a correction term in the sublimation formula of Thorpe and Mason. The correction term accounts empirically for transient particle temperatures in the lowest 0.3 m of the atmosphere but requires further validation in a wider range of conditions. When estimating the particle mixing ratios in the one-dimensional model, an improved vertical discretization is critical. Overall, the proposed improvements change the latent heat flux by up to 102 W m-2 (or 67%). To reduce the remaining errors, the saltation-suspension interface and near-surface particle speed should be better parameterized.

Stable water isotopes (SWIs) contain valuable information on the past climate and phase changes in the hydrologic cycle. Recently, vapour measurements in the polar regions have provided new insights into the effects of snow-related and atmospheric processes on SWIs. The purpose of this study is to elucidate the drivers of the particularly depleted vapour isotopic composition measured on a ship close to the East Antarctic coast during the Antarctic Circumnavigation Expedition in 2017. Reanalysis data and backward trajectories are used to model the isotopic composition of air parcels arriving in the atmospheric boundary layer (ABL) above the ship. A novel approach is developed to account for moisture exchanges with the snow surface. The model generally reproduces the observed trend with strongly depleted vapour δ18O values in the middle of the 6-day study period. This depletion is caused by direct air mass advection from the ice sheet where the vapour is more depleted in heavy SWIs due to distillation during cloud formation. The time spent by the air masses in the marine ABL shortly before arrival at the ship is crucial as ocean evaporation typically leads to an abrupt change in the isotopic signature. Snow sublimation is another important driver because the air masses and the sublimation flux will differ substantially in their isotopic composition if the air masses cross the ocean-snow boundary or descend from higher atmospheric levels. Although our model makes strong simplifications, it is a useful and computationally efficient method for understanding SWI dynamics at polar sites.

The surface of the Earth is snow-covered at least seasonally over large areas. This snow surface is highly dynamic, particularly under the influence of strong winds. The motion of snow particles driven by the wind not only changes the snow cover but has important consequences for the atmosphere in that it adds mass and moisture and extracts heat. Large scale meteorological and climatological models neglect these surface dynamics or produce conflicting results from too simplified process representation. With recent progress in the detailed understanding of the saltation process, in particular with respect to sand saltation, and the advancement of numerical models, we can systematically investigate the influence of snow properties on saltation. This contribution uses a Large Eddy Simulation (LES) model with full surface particle dynamics to investigate how snow cohesion and size distribution influence saltation dynamics and in particular the total mass flux. The model reproduces some known characteristics of the saltation system such as a focus point or a constant near surface particle speed. An interesting result is that cohesion and grain size heterogeneity can increase the overall saltation mass flux at high friction velocities. Moreover, some simplified models agree reasonably well with the simulations for given bed characteristics, while others clearly do not. These results are valid for continuous saltation while intermittent saltation, which often occurs in nature, needs further investigation. In order to successfully parameterize saltation in large scale models, progress must be made in correctly representing snow surface properties in these models, in particular cohesion.