Polar low

Polar low, originally uploaded by Erik Kolstad.

This is a beautiful polar low in the Barents Sea on the 20th of December 2002. ’Polar low’ is the denomination of a wide range of weather phenomena at high latitudes. Although many definitions have been proposed, the following one was given by Rasmussen and Turner in the book "Polar lows" from 2003:

A polar low is a small, but fairly intense maritime cyclone that forms poleward of the main baroclinic zone (the polar front or other major baroclinic zone). The horizontal scale of the polar low is approximately between 200 and 1000 kilometres and surface winds near or above gale force.

A 'baroclinic zone' is a region with large local temperature differences, which are the primary source of 'fuel' for most cyclones outside the tropics ('extratropical cyclones').

Although we now know that polar lows can occur in both hemispheres (a polar low-like feature has even been observed over the Mediterranean), they were first noticed in the Nordic Seas, or more specifically along the coast of Norway.

Read more about polar lows in this article from the Group for Earth Observation (GEO) or on Wikipedia. I wrote my PhD thesis about them.