A most beautiful polar low. A case study of a polar low development in the Bear Island region

Abstract

Satellite images from 26 and 27 February 1987 of the Bear Island region show the formation of a polar low with an unusual symmetric cloud field around a central eye, which strongly resembles a small-scale tropical storm. Conventional observations as well as output from a limited area numerical model are scrutinized to understand the dynamics of the low and to determine whether the development and structure of the polar low actually corresponds to that of a tropical cyclone. The discussion is based upon potential vorticity arguments. The data shows that the analogy between this particular polar low and tropical storms is not limited to the structure of the cloud field. However, the low develops in a baroclinic environment and is triggered by an upper-level potential vorticity anomaly. The upper level forcing diminishes after the initial triggering phase. The possibility of a self-induced development during the maintenance phase from the release of latent heat is discussed.