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.
Atmospheric mercury (Hg) can be operationally defined into three types: gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM), and particle-bound Hg (PBM). GEM is the most abundant Hg species in the global atmosphere (approximately 90%) and is well mixed due to its prolonged lifetime (0.5-1 year) and stable chemical properties. As GOM and PBM are more soluble in water than GEM and have a shorter lifetime (days to weeks), they are the predominant Hg species deposited to ecosystems through wet and dry deposition (Selin, 2009). The mutual transformations between these three Hg species have an important influence on the transportation and deposition of atmospheric Hg on a global scale (Schroeder & Munthe, 1998). The marine boundary layer (MBL) represents the atmospheric area affected by the oceanic surface, and its height significantly varies between middle-high latitudes (dozens to hundreds of meters) and low latitudes (up to 2000 m) (Hedgecock et al., 2005). The circulation of atmospheric Hg in the MBL differs from that in the planetary boundary layer (PBL) because of the significant differences in meteorological conditions and chemical compositions between the MBL and the PBL (e.g., humidity, sea salt aerosols, and oxidation mechanisms) (
• Distribution patterns of sea salt aerosol mass concentrations differed significantly between sea areas at different latitudes • Inter-annual changes in sea salt aerosol concentrations in different sea areas were not synchronized • GEOS-Chem using a single sea surface temperature scale to correct the sea salt emission led to underestimation in the Southern Ocean
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