The Life-Cycle of a Polar Low Observed with Research Aircraft Dropsondes

The structure and life cycle of a polar low that formed over the ocean south of the Fram Strait on 3 and 4 March 2008 is described using GPS dropsondes from the DLR Falcon research aircraft and by AVHRR satellite images. Data from three successive flights during the life cycle of the polar low will be presented. The Norwegian IPY-THORPEX project carried out a field experiment between February and May 2008, aiming at investigating adverse weather in the Arctic. During the campaign period, the DLR Falcon aircraft was stationed at Andoya Airport in Northern Norway. On the evening 2 March the synoptic scale flow triggered a cold-air outbreak in the Fram Strait and the western Barents Sea. The weather analysis from the Norwegian weather service (met.no)indicated strong reversed shear flow (warm air to the left) and favorable conditions for the formations of polar lows. A flight for the next morning was planned. At the time of departure AVHRR satellite images of deep-convective clouds revealed the presence of an Arctic front in the northerly winds between Greenland and the Svalbard islands. During this flight 18 dropsondes were successfully released. A second flight was carried out later the same day, 3 March. At this time a meso-scale cyclone had formed at the southern tip of the Arctic Front. The cyclone was measured in three cross-sections with 14 successful sondes released. The night between 3 and 4 March the cyclone intensified and by the third flight a mature polar low was located outside the coast of Trondelag in Norway. The last flight was carried out, staring on the morning 4 March, making 4 cross-sections with 20 dropsondes. On the evening 4 March, shortly after the third flight, the polar low made landfall and faded rapidly.