Abstract
Data from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition allowed us to investigate the temporal dynamics of snowfall, snow accumulation, and erosion in great detail for almost the whole accumulation season (November 2019 to May 2020). We computed cumulative snow water equivalent (SWE) over the sea ice based on snow depth (HS) and density retrievals from a SnowMicroPen (SMP) and approximately weekly-measured snow depths along fixed transect paths. Hence, the computed SWE considers surface heterogeneities over an average path length of 1469 m. We used the SWE from the snow cover to compare with precipitation sensors installed during MOSAiC. The data were compared with ERA5 reanalysis snowfall rates for the drift track. Our study shows that the simple fitted HS-SWE function can well be used to compute SWE along a transect path based on SMP SWE retrievals and snow-depth measurements. We found an accumulated snow mass of 34 mm SWE until 26 April 2020. Further, we found that the Vaisala Present Weather Detector 22 (PWD22), installed on a railing on the top deck of research vessel Polarstern was least affected by blowing snow and showed good agreements with SWE retrievals along the transect, however, it also systematically underestimated snowfall. The OTT Pluvio2 and the OTT Parsivel2 were largely affected by wind and blowing snow, leading to higher measured precipitation rates, but when eliminating drifting snow periods, especially the OTT Pluvio2 shows good agreements with ground measurements. A comparison with ERA5 snowfall data reveals a good timing of the snowfall events and good agreement with ground measurements but also a tendency towards overestimation. Retrieved snowfall from the ship-based Ka-band ARM Zenith Radar (KAZR) shows good agreements with SWE of the snow cover and comparable differences as ERA5. Assuming the KAZR derived snowfall as an upper limit and PWD22 as a lower limit of a cumulative snowfall range, we estimate 72 to 107 mm measured between 31 October 2019 and 26 April 2020. For the same period, we estimate the precipitation mass loss along the transect due to erosion and sublimation as between 53 and 68 %. Until 7 May 2020, we suggest a cumulative snowfall of 98–114 mm.
Highlights
Snow cover on sea ice has many significant effects on the ice mass balance and general heat exchange processes between the ocean and the atmosphere
It can be observed that the standard deviation increased for both loops over time (Fig. 9), though it was initially higher for the rougher deformed ice (35 mm on 31 October 2019) than for remnant, or first-year ice (FYI)
We could show that snow water equivalent (SWE) differences between snow on deformed secondyear ice (SYI) and snow on remnant SYI and FYI decrease until the end of the snow accumulation season at the beginning of May
Summary
Snow cover on sea ice has many significant effects on the ice mass balance and general heat exchange processes between the ocean and the atmosphere. The largest sink term in Eq. is the erosion outside the melting season, represented as D in the mass balance equation, which may make up to 50 % SWE decrease over sea ice of the total precipitated snow mass (Leonard and Maksym, 2011). Leonard et al. (2008); Leonard and Maksym (2011) were doing computations with the same model-base for Antarctic sea ice, but considering saltation mass flux in addition They emphasize the relative importance of saltation mass flux in the computation, as they find that all saltated mass flux blown towards an open lead vanishes there, and that the mass flux within the saltation layer is lower than in the blowing snow column above, the higher frequency of saltation (about 50 % on 23 days in October 2007) compared against blowing snow frequency makes the mass loss due to saltation an important term.
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