Precipitation over Greenland and its relation to the North Atlantic Oscillation

The omega equation method based on an equivalent isobaric geopotential heig ht in sigma coordinates has been used to retrieve the precipitation over Gr eenland. This approach is designed to accurately represent the topographic effects of the Greenland Ice Sheet on atmospheric motion and precipitation. The 11 year mean precipitation from 1985 to 1996 over all of Greenland is 376 mm yr(-1), which is close to the long-term mean precipitation of 346 mm yr(-1) estimated from glaciological data. The precipitation over all of Gr eenland shows that the largest value in 1986 is 472 mm yr(-1) and the small est value in 1995 is 309 mm yr(-1). The major interannual variability of th e atmospheric circulation in the North Atlantic can be represented by the v ariation of the North Atlantic Oscillation (NAO) index, which is most prono unced during winter. It is found that if the NAO index increases, the total precipitation over Greenland decreases, and vice versa. The correlation co efficient between these two series for 1985-1995 is -0.75. The mean precipi tation over southern Greenland, where the majority of precipitation falls, is more closely related to the NAO index in winter, and their correlation c oefficient is -0.80. This relationship can be understood from the composite maps of sea level pressure and Greenland precipitation for the high and lo w index months. During months of high NAO index values, the Icelandic Low i s strong. During months of low NAO index values, the monthly mean low is lo cated to the southwest of Greenland over the Labrador Sea. Precipitation am ounts over the southeast coast of Greenland are about 100 mm larger during the low NAO index months than the high NAO index months. Precipitation over all of Greenland during the low NAO index months is higher. There are sign ificant downward trends in annual precipitation from 1985-1995 for all of G reenland and its southern and central west coastal regions, amounting to ab out 3% per year.