A MESOSCALE MODEL-BASED STUDY OF THE DYNAMICS OF A WINTERTIME POLAR LOW IN THE WEDDELL SEA REGION OF THE ANTARCTIC DURING THE WINTER WEDDELL SEA PROGRAM FIELD PHASE 1986

A wintertime mesocyclone (MC) event occurring during the Winter Weddel l Sea Program field phase 1986 is studied by digital advanced very hig h-resolution radiometer data and numerical simulations using the mesos cale Norwegian Limited Area Model. The MC considered developed during July 30, 1986, near the sea ice front of the northern Weddell Sea. Dur ing its initial and developmental phases it moved eastward parallel to the sea ice front. During the first 24 hours, baroclinic instability and diabatic heating were found to be of great importance for the inte nsification. During its mature stage (the following 24 hours), a prono unced frontal system formed, and baroclinic instability can be regarde d as the main process for its further development. The MC moved over t he sea ice during its mature stage, so the forcing by surface energy f luxes was less important. A cyclonic upper level potential vorticity a nomaly was found to be present during the mature stage. The MC had a d iameter of about 700 km and a lifetime of more than 48 hours and reach ed the intensify of a polar low (measured near-surface wind speeds of up to 26 m/s). The model results revealed good agreement with observat ions (radiosondes and synoptic observations) in the case of the ''full physics'' run, but in the case of the ''no cloud physics'' run this w as very poor.