Extreme convection in the Lofoten Basin of the Norwegian Sea

Abstract

<p>One of the factors affecting the variability of the global climate is strong oceanic convection. Current research declares the results of the investigation on the extreme convection in the Lofoten Basin (LB) using the Argo profilers data. The most common parameter reflecting the convection intensity is Mixed Layer Depth (MLD). In the frames of the understudied period, MLD exceeds 1000 m in March-April and December 2010 in the Lofoten Basin Eddy (LBE), whereas the average MLD is about 200 m and rarely exceeds 400 m in the basin. Water volume formed at mid-depth of the central LB, between 1000 m depth and the isosteric surface s07 is connected with the extreme convection events. We analytically assess the final mixing depth that corresponds well to measured values of the MLD. Such a correspondence indicates the variations in the buoyancy flux and stratification as the main reasons for MLD variability in the LB. We easily explain this variability due to heat release in the basin. Atmospheric patterns during the extreme convection are described. It occurs that northerly winds are as common as dominating south-westerly winds during the months with extreme convection. 32 cases of extreme convective events with MLD exceeding 350 m were analyzed and we reveal that correspondent composite maps of Sea Level Pressure (SLP) and surface heat flux match well NAO-/EAP- atmospheric pattern in the Northern Atlantic, while negative NAO pattern prevails in climate during winter-spring. We define the heat release as the major trigger of strong convection. Heat release associated with extreme convection events in the LB is twice stronger than usual.</p>