Meteorological Conditions During the MOSAiC Expedition: Normal or unusual?

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition was the largest polar research expedition ever conducted and took place from October 2019 to September 2020 in the central Arctic. The expedition was based around the German research icebreaker Polarstern, which drifted with the sea ice across the Arctic from north of Siberia to the North Atlantic Ocean. The primary observations from MOSAiC were made at a central observatory, on the sea ice, adjacent to the Polarstern. The expedition involved hundreds of scientists from over 20 countries observing the atmosphere, ocean, ice, biogeochemistry and ecosystems of the central Arctic.

In this presentation we will assess how normal or unusual the weather experienced at the Polarstern and the MOSAiC central observatory was during the MOSAiC year from October 2019 to September 2020. ERA5 reanalysis data of near surface meteorology and surface radiative fluxes along the MOSAiC trajectory are compared to ERA5 data from 1979 to 2019 to place the MOSAiC year weather into a longer term climate context. Overall, the near surface state during the MOSAiC year fell within the 1979 to 2019 values seen in ERA5 although some months had a larger than expected number of times with near surface state or fluxes outside of the prior 40 year interquartile range and several daily records were noted, usually associated with storm events. The winter and spring period (February to June 2020) was characterized by more frequent and stronger storm events than was typically seen in the ERA5 record from 1979 to 2019. This stormy period was associated with a shift to a strong positive Arctic Oscillation phase from January to March 2020. The MOSAiC summer was warmer than the prior 40 years with July and August 2020 having the warmest and wettest conditions in the ERA5 since 1979. The melt season along the MOSAiC trajectory was nearly a month longer than 1979-2019 median in ERA5. The results presented here will help scientists interpret the MOSAiC observations by providing a long-term climate context for the MOSAiC year.