Drifting snow climate of the Greenland ice sheet: a study with a regional climate model

Abstract

Abstract. This paper presents the drifting snow climate of the Greenland ice sheet, using output from a high-resolution (∼ 11 km) regional climate model. Because reliable direct observations of drifting snow do not exist, we evaluate the modeled near-surface climate instead, using automatic weather station (AWS) observations from the K-transect and find that RACMO2 realistically simulates near-surface wind speed and relative humidity, two variables that are important for drifting snow. Integrated over the ice sheet, drifting snow sublimation (SU ds ) equals 24±3 Gt yr −1 , and is significantly larger than surface sublimation (SU s , 16 ± 2 Gt yr −1 ). SU ds strongly varies between seasons, and is only important in winter, when surface sublimation and runoff are small. A rapid transition exists between the winter season, when snowfall and SU ds are important, and the summer season, when snowmelt is significant, which increases surface snow density and thereby limits drifting snow processes. Drifting snow erosion (ER ds ) is only important on a regional scale. In recent decades, following decreasing wind speed and rising near-surface temperatures, SU ds exhibits a negative trend (0.1 ± 0.1 Gt yr −1 ), which is compensated by an increase in SU s of similar magnitude.

Evaluation of the updated regional climate model RACMO2.3: summer snowfall impact on the Greenland Ice Sheet

“…Moreover, under marginally freezing conditions, i.e., between −7 and −1 • C, precipitation occurs exclusively as snowfall even though the precipitating clouds are mixed phase. In the previous model version, similar atmospheric conditions could also have resulted in a mix of liquid and solid precipitation for temperatures above −7 • C. The update results in improved relative contributions of rainfall and snowfall to the total precipitation flux (Lin et al, 1983). Furthermore, the cloud water-to-snowfall conversion coefficient now remains constant for liquid (> 0 • C) and mixed phase clouds (−23 to 0 • C) whereas it decreases with temperature for ice clouds (< −23 • C), resulting in slower snowfall production.…”

Firn Meltwater Retention on the Greenland Ice Sheet: A Model Comparison

“…This model is specifically adapted to simulate climate conditions over ice sheets and contains a multilayer snow model, physically identical to the IMAU-FDM but with fewer vertical layers, an albedo scheme based on prognostic snow grain size (Kuipers Munneke et al, 2011) and a drifting snow routine (Lenaerts et al, 2012). RACMO2.3 was run for the period 1958-2015 on an 11 km horizontal resolution grid and a domain including Greenland, Iceland, Svalbard, and part of arctic Canada.…”

A Characterization of Greenland Ice Sheet Surface Melt and Runoff in Contemporary Reanalyses and a Regional Climate Model

“…Ice sheet surface mass balance (SMB), which hereafter denotes the sum of surface plus internal mass balance (i.e., climatic mass balance; Cogley et al, 2011), may be approximated as precipitation minus the net of evaporation and runoff. Other terms including blowing snow are considered negligible here (e.g., Loewe, 1970), although recent studies have estimated substantial values for the GrIS (e.g., Lenaerts et al, 2012). As typically defined in models, precipitation is the sum of solid plus liquid components reaching the surface, the evaporation variable actually refers to the net vertical flux of the vapor phase of water at the surface.…”