Air‐Ice‐Ocean Coupling During a Strong Mid‐Winter Cyclone: Observing Coupled Dynamic Interactions Across Scales.

Arctic cyclones are key drivers of sea ice and ocean variability. During the 2019–2020 Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, joint observations of the coupled air‐ice‐ocean system were collected at multiple spatial scales. Here, we present observations of a strong mid‐winter cyclone that impacted the MOSAiC site as it drifted in the central Arctic pack ice. The sea ice dynamical response showed spatial structure at the scale of the evolving and translating cyclonic wind field. Internal ice stress and ocean stress play significant roles, resulting in timing offsets between the atmospheric forcing and the ice response and post‐cyclone inertial ringing in the ice and ocean. Ice motion in response to the wind field then forces the upper ocean currents through frictional drag. The strongest impacts to the sea ice and ocean from the passing cyclone occur as a result of the surface impacts of a strong atmospheric low‐level jet (LLJ) behind the trailing cold front and changing wind directions between the warm‐sector LLJ and post cold‐frontal LLJ. Impacts of the cyclone are prolonged through the coupled ice‐ocean inertial response. Local impacts of the approximately 120 km wide LLJ occur over a 12 hr period or less and at scales of a kilometer to a few tens of kilometers, meaning that these impacts occur at combined smaller spatial scales and faster time scales than most satellite observations and coupled Earth system models can resolve. Plain Language Summary: Arctic winter cyclones are an important part of the Arctic climate system. Yet, due to sparse observations, processes of the coupled sea ice‐ocean response to cyclones are not fully understood. During the 2019–2020 Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, observations of the atmosphere, sea ice, and ocean were collected at a range of spatial scales. Here, we describe the atmospheric structure and coupled ice‐ocean response to a strong winter cyclone using data from surface weather stations, weather balloons, radar, and a weather model. We then describe the sea ice motion using a large set of global positioning system buoys and ice radar images. Finally, we examine the upper ocean currents and structure using ocean buoy data. The most important part of the storm structure for the sea ice is the development of an atmospheric low‐level jet (LLJ), a narrow region of fast‐moving air that eventually circles around the storm. The sudden change in ice drift speed at the time that the LLJ passes overhead enhances motion of the ice and ocean. Periodic currents in the ocean initiated by the sudden wind change of the LLJ continue for days following the passage of the storm, prolonging its effects. Key Points: A strong cyclone crossed the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) in midwinter 2020Detailed, multi‐platform observations enable characterization of coupled air‐ice‐ocean interactions during the passage of the cycloneThe development of a low‐level atmospheric jet is a key factor in the spatially and temporally varying sea ice‐ocean response to the storm [ABSTRACT FROM AUTHOR]