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

Abstract

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 snow conditions have been mainly described through modelling studies and few field 10 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 15 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 % 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 m is observed in only 9.6 % of the drifting snow occurrences or 5.9 % of the time and mainly occurs in 20 strong wind speed and drift conditions. This relatively 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. 25

Drifting snow statistics from multiple-year autonomous measurements in Adelie Land, eastern Antarctica

“…On an annual basis, both kinds of events combine to produce yearly values ofclose to or above 2 10 6 kg m -2 at both locations (Table 2). Such high estimates suggest that redistribution of snow by wind together with concurrent sublimation of snow particles during transport are important components of the surface mass balance 300 in Adelie Land (Agosta et al, 2012;Amory and Kittel, 2019).…”