Wintertime roll and cell convection over Greenland and Barents Sea regions: A climatology

Wintertime cold-air outbreaks from the polar ice and land surfaces over the open sea lead to organized convective patterns (OCP) in the atmosphere, vi sible as cloud streets and cellular cloud structures on satellite images. L arge amounts of energy are transferred from the ocean to the atmosphere and convective organized flows contribute substantially to the vertical fluxes of heat, moisture and momentum in the boundary layer. However, little is k nown about the frequency of OCP occurrence. The paper is aimed to fill this gap and presents a climatology of OCP occurrence over the Greenland Sea an d Barents Sea. The study is based on daily NOAA satellite images of 10 wint ers (November till March) for the years from 1985/1986 to 199411995. It cov ers the area from 70 degrees N to 82.5 degrees N and from 20 degrees W to 6 0 degrees E and is subdivided into 40 subareas with a grid size of 10 degre es in longitude and 2.5 degrees in latitude. OCP occur in more than 50 % of the time averaged over the 10 winters. Complete absence of OCP is observed in less than 5 % of the time. OCP occur most frequently over the Westspits -bergen current and around the border between the Greenland Sea and the Bar ents Sea. Cloud streets are the dominating OCP mode close to the ice edge, whereas cellular structures dominate at farther distances. Variability of O CP occurrence may be large on all timescales. A relation between ice extent and frequenzcy of OCP occurrence is present occasionally.