A Climatology of Polar Low Occurrences in the Nordic Seas and an Examination of Katabatic Winds as a Triggering Mechanism
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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This study examines polar low formation frequency, origin region and storm tracks in the entire Nordic Sea region for a complete polar low season and identifies the prevailing synoptic situation common to polar low formation. The number of polar lows detected through TIROS-N satellite imagery between September 1988 and May 1989 was significantly greater than one would expect from previous studies. Many polar lows were detected over the land areas of Greenland, Iceland and Svalbard away from a direct surface heat source. The storms detected over Greenland generally formed at the outflows of glacial valleys. To determine probable formation areas, polar lows were linearly backtracked along the reciprocal of their storm tracks. A significant number were backtracked to glacier outflows. These formation locations suggest a katabatic influence on storm formation, possibly due to vortex stretching, or the enhancement and distortion of an over-ice or over-land boundary layer baroclinic zone. Katabatic flows were examined by analyzing one month of regional surface synoptic observations and NOGAP 1000 mb height gradients. To develop aids to enhance polar low forecasting, monthly mean 1000 and 500 mb fields for chart times closest to polar low detection, or time backtracked to Northern, Central and Southern Greenland, were calculated from archived NOGAPS 12 hourly analyses and compared to the monthly averaged climatology fields of height and temperature.
- Physical and Dynamic Oceanography