Meteorological conditions during the MOSAiC expedition

Abstract

This article sets the near-surface meteorological conditions during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition in the context of the interannual variability and extremes within the past 4 decades. Hourly ERA5 reanalysis data for the Polarstern trajectory for 1979–2020 are analyzed. The conditions were relatively normal given that they were mostly within the interquartile range of the preceding 4 decades. Nevertheless, some anomalous and even record-breaking conditions did occur, particularly during synoptic events. Extreme cases of warm, moist air transported from the northern North Atlantic or northwestern Siberia into the Arctic were identified from late fall until early spring. Daily temperature and total column water vapor were classified as being among the top-ranking warmest/wettest days or even record-breaking based on the full record. Associated with this, the longwave radiative fluxes at the surface were extremely anomalous for these winter cases. The winter and spring period was characterized by more frequent storm events and median cyclone intensity ranking in the top 25th percentile of the full record. During summer, near melting point conditions were more than a month longer than usual, and the July and August 2020 mean conditions were the all-time warmest and wettest. These record conditions near the Polarstern were embedded in large positive temperature and moisture anomalies over the whole central Arctic. In contrast, unusually cold conditions occurred during the beginning of November 2019 and in early March 2020, related to the Arctic Oscillation. In March, this was linked with anomalously strong and persistent northerly winds associated with frequent cyclone occurrence to the southeast of the Polarstern.

MOSAiC drift expedition from October 2019 to July 2020: sea ice conditions from space and comparison with previous years

“…The monthly maps reveal anomalously high lead frequencies north of Greenland and Ellesmere Island between November 2019 and January 2020. Moreover, the strong positive anomalies in the Barents Sea in January 2020 and in the Beaufort Sea in February-March 2020 are worth mentioning (Rostosky et al, 2018(Rostosky et al, , 2020. The blue and yellow line gives the mean snow depth at a 50 and 100 km radius for comparison.…”

“…Low-resolution snow depth along the MOSAiC trajectory is retrieved from the 7 and 19 GHz channels of the AMSR-E 3902 T. Krumpen et al: MOSAiC drift from October 2019 to July 2020 and AMSR2 microwave radiometer, following the method from Rostosky et al (2018). Data are available via Rostosky et al (2019a, b).…”

“…The grid size of the snow depth data is 25 km. The snow depth retrieval for multi-year ice areas is currently limited to March and April, while for first-year ice it can be retrieved all winter (see Rostosky et al, 2018). As the MOSAiC ice floe was in an area of predominantly second-year ice, which radiometrically is considered multi-year ice for the snow depth retrieval, snow depth for MOSAiC is only available for March and April.…”

“…The thin gray lines show the individual years (2005 to 2019), and the green line provides the climatological mean. Because the MOSAiC floe was located in an area with partly second-year ice, snow depth can only be retrieved for March and April (Rostosky et al, 2018). (compare Dethloff et al, 2021).…”

“…For the MOSAiC year 2020, the thick black line shows snow depth at 12.5 km radius. The gray shaded area indicates the corresponding uncertainty bounds(Rostosky et al, 2018(Rostosky et al, , 2020. The blue and yellow line gives the mean snow depth at a 50 and 100 km radius for comparison.…”