ALBERT

Description: With the Arctic rapidly changing, the needs to observe, understand, and model the changes are essential. To support these needs, an annual cycle of observations of atmospheric properties, processes, and interactions were made while drifting with the sea ice across the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. An international team designed and implemented the comprehensive program to document and characterize all aspects of the Arctic atmospheric system in unprecedented detail, using a variety of approaches, and across multiple scales. These measurements were coordinated with other observational teams to explore cross-cutting and coupled interactions with the Arctic Ocean, sea ice, and ecosystem through a variety of physical and biogeochemical processes. This overview outlines the breadth and complexity of the atmospheric research program, which was organized into 4 subgroups: atmospheric state, clouds and precipitation, gases and aerosols, and energy budgets. Atmospheric variability over the annual cycle revealed important influences from a persistent large-scale winter circulation pattern, leading to some storms with pressure and winds that were outside the interquartile range of past conditions suggested by long-term reanalysis. Similarly, the MOSAiC location was warmer and wetter in summer than the reanalysis climatology, in part due to its close proximity to the sea ice edge. The comprehensiveness of the observational program for characterizing and analyzing atmospheric phenomena is demonstrated via a winter case study examining air mass transitions and a summer case study examining vertical atmospheric evolution. Overall, the MOSAiC atmospheric program successfully met its objectives and was the most comprehensive atmospheric measurement program to date conducted over the Arctic sea ice. The obtained data will support a broad range of coupled-system scientific research and provide an important foundation for advancing multiscale modeling capabilities in the Arctic.

Description: To assess weather forecast and climate models, it is necessary to have observations going beyond standard variables, to reveal underlying processes. However, such observations are scarce over the central Arctic Ocean, with not even accurate observations of atmospheric vertical structure. Therefore, it is crucial to gather detailed atmospheric observations during icebreaker-based research expeditions to the central Arctic. In this study, we analyze extensive observations collected during the Arctic Ocean 2018 expedition on the icebreaker Oden. This took place in summer of 2018, with a focus on a month-long period from August 12 to September 14 while drifting with sea-ice near the North Pole. We evaluate 125 3-day forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS). Our analysis reveals a distinct systematic vertical error structure, with a boundary layer that is too warm with a kilometer-deep layer immediately above that is too cold. This error grows as the melt ends and the surface begins to freeze and also displays a diurnal variation. Additionally, the IFS overestimate low-troposphere clouds, with strong effects on the surface energy budget. Clear periods that occur in reality never materialize in the model. Initially errors are smaller, likely due to assimilation of the expeditions soundings, but grow rapidly and persist throughout the forecasts. We propose that the errors are due to parameterized sub-grid scale convection. Since the evaluated forecast model (Cy45r1) is almost identical to that used for ERA5, we expect these errors to be present also in the reanalysis.