Severe Marine Weather Systems During Freeze-Up in the Chukchi Sea: Cold-Air Outbreak and Mesocyclone Case Studies From Satellite Multisensor Measurements and Reanalysis Datasets

Abstract

In the present article, cold-air outbreak (CAO) and polar low (PL) events were examined over the Chukchi Sea during low sea ice extent of the basin in the November–December period, 2015. An analysis of weather events was performed using multisensor satellite measurements, the NCEP Climate Forecast System, version 2 (CFSv2), and Arctic System Reanalysis, version 2 (ASR2). The CFSv2 data showed that the most intense cold advection occurred at the 1000–900 hPa boundary layer. It was shown that CAO had been developing from November 30 to December 6 and was accompanied by the sea surface wind speed exceeding 20 m/s and rapid formation and drift of sea ice. Analysis of the sea ice response to the CAO showed fast freezing of the Chukchi Sea for seven days indicating excessive heat loss of the water basin. In addition, significant increase in the open and very open ice areas was observed. These areas could be exposed to excessive cold atmosphere, releasing heat into the atmosphere. PL events have been identified during intensive mesocyclogenesis over the sea during 15–17 November. Weather conditions were characterized by the values of wind speed reaching 15–17 m/s and dry air with total water vapor content (5–7 kg/m2). Analysis of the synthetic aperture radar image revealed the position and horizontal size of the meso-α-cyclone, the fine structure of the mesoscale frontal system of the PL forming meso-γ-vortices, and the wave-like line of the horizontal wind shear in the local convergence zone. The representation of PL events in sea level pressure and near-surface wind speed fields from the ASR2 and CFSv2 datasets was ambiguous. However, the satellite-based and CFSv2 wind speeds better agreed for high-wind conditions.