Description: A radiation station was installed on drifting sea-ice in the Arctic Ocean during the MOSAiC expedition between November 2019 and September 2020. The station measured all the components of the surface radiation budget, that is the broadband downwelling and upwelling shortwave and longwave irradiance, as well as the downward direct and diffuse partitioning of downwelling irradiance. The dataset contains the raw data and the calibrated radiative fluxes recorded at two second temporal resolution for the entire annual cycle of the MOSAiC expedition. The data are not quality checked and occasionally suffer from frost accumulation on the domes of the sensors. Breaks in the dataset occur when the station was removed from the sea-ice, before the research vessel Polarstern temporarily left the ice floe in May 2020 and before the disintegration of the original ice floe in July 2020. The station was installed at the Central Observatory (CO1, CO2, CO3) of MOSAiC on first-year sea-ice: from 12th of November 2019 to 10th of May 2020 the station was located over a rather uniform snow-covered surface, while from the 10th to the 28th of July 2020 it was re-deployed over a ~5m wide sea-ice strip in between two melt-ponds. From 27th of August to 18th of September 2020 the station was installed on a different drifting ice floe at the edge of a melt pond, with the downward facing sensors being over the melt pond. The station did not have its own GPS but each data reading is associated with Master track of Polarstern published in: PS122/1: doi:10.1594/PANGAEA.924669, PS122/2: doi:10.1594/PANGAEA.924672, PS122/3: doi:10.1594/PANGAEA.924678, PS122/4: doi:10.1594/PANGAEA.926830, PS122/5: doi:10.1594/PANGAEA.926911 The drift tracks of the Central Observatories are published here: CO1: doi:10.1594/PANGAEA.937184, CO2: doi:10.1594/PANGAEA.937186, CO3: doi:10.1594/PANGAEA.937187

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.