Brief communication: Rare ambient saturation during drifting snow occurrences in coastal East Antarctica

Charles Amory, Christoph Kittel
2019 The Cryosphere Discussions  
<p><strong>Abstract.</strong> Sublimation of snow particles during transport has been recognized as the main ablation process on the Antarctic ice sheet. The resulting increase in moisture content and cooling of the ambient air are thermodynamic negative feedbacks that both contribute to increase the relative humidity of the air, inhibiting further sublimation when saturation is reached. This self-limiting effect and the associated development of saturated near-surface air layers in drifting
more » ... yers in drifting snow conditions have been mainly described through modelling studies and few field observations. A set of meteorological data including drifting snow mass fluxes and vertical profiles of relative humidity collected at site D17 in coastal Adelie Land (East Antarctica) during year 2013 is used to study the relationship between saturation of the near-surface atmosphere and the occurrence of drifting snow in a katabatic wind region among the most prone to snow transport by wind. Atmospheric moistening by the sublimation of the windborne snow particles generally results in a strong increase in relative humidity with the magnitude of drifting snow and a decrease of its vertical gradient, suggesting that windborne-snow sublimation can be an important contributor to the local near-surface moisture budget. Despite a high incidence of drifting snow at the measurement location (61.3&amp;thinsp;% of the time), saturation, when attained, is however most often limited to a thin air layer below 2 meters above ground. The development of a near-surface saturated air layer up to the highest measurement level of 5.5&amp;thinsp;m is observed in only 9.6&amp;thinsp;% of the drifting snow occurrences or 5.9&amp;thinsp;% of the time and mainly occurs in strong wind speed and drift conditions. This rare occurrence of ambient saturation is explained by the likely existence of moisture-removal mechanisms inherent to the katabatic nature of the boundary-layer flow that weaken the negative feedback of windborne-snow sublimation. Such mechanisms, potentially quite active in katabatic-generated windborne-snow layers all over Antarctica may be very important in understanding the surface mass and atmospheric moisture budgets of the ice sheet by enhancing windborne-snow sublimation.</p>
doi:10.5194/tc-2019-165 fatcat:f4iq35nl5fezlddcsads5ec3je