PRECIPITATION OVER GREENLAND RETRIEVED BY A DYNAMIC METHOD AND ITS RELATION TO CYCLONIC ACTIVITY

In order to calculate the vertical motion over some high mountain regi ons, such as Greenland, an omega-equation without the quasigeostrophic approximation in sigma-coordinates has been developed. A dynamic meth od for retrieving precipitation over Greenland is based on this omega- equation. The retrieved annual mean precipitation distribution for 198 7 and 1988 is in very good agreement with the observed annual accumula tion pattern over the Greenland Ice Sheet. The major weather system pr oducing precipitation over Greenland is the frontal cyclone. Based on the precipitation characteristics, Greenland can be divided into five subregions. Precipitation over the north coastal and central interior regions primarily occurs in summer. For the three other subregions, if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed, a clear relationship b etween precipitation and cyclonic activity emerges. If a mean cyclone exists in the Labrador Sea, heavy precipitation will fall over Greenla nd during that month. By contrast, if a mean cyclone exists near Icela nd, precipitation over Greenland will be reduced. This is an important relationship between Greenland precipitation and cyclonic activity. T he cyclonic tracks near Greenland are established. A synoptic example is used to show the relation between precipitation and a cyclone movin g up the west side of Greenland (track B) combined with movement acros s the southern tip of the island (track C). In this example, lee cyclo genesis is caused by the southern part of the Greenland Ice Sheet. The lee cyclone develops on the east coast along track C. During lee cycl ogenesis, heavy precipitation falls over the southern region. The ''pa rent'' cyclone moves along track B, and precipitation falls along the west coast of Greenland. A possible feedback between cyclonic activity and the mass balance of the Greenland Ice Sheet is proposed. On the o ne hand, cyclonic activity has a significant influence on snow accumul ation over the ice sheet. The development of Icelandic cyclones is not favorable for precipitation over Greenland. On the other hand, the Gr eenland Ice Sheet has an important dynamic effect in producing lee cyc logenesis and affecting the frequency of Icelandic cyclones. This poss ible feedback may be important for understanding how the mass balance of the Greenland Ice Sheet and the Icelandic low are maintained in the present climate state.