An Investigation of a Polar Low with a Spiral Cloud Structure

Abstract

A synoptic case study where a small-scale low, a so-called polar low, can be followed as a closed circulation on the surface maps around 2O00 km from Iceland to the North Sea is presented. Satellite images show that the polar low develops a cloud pattern of convective clouds very much like that of a tropical cyclone. The 1000?500 mb thickness field shows that the polar low has a warm core during the time when it is best developed. It is concluded that the polar low discussed in this work probably is a phenomenon different from a comma cloud and also different from small-scale vortices associated with strong mid-tropospheric positive vorticity advection.