Precipitation over Greenland and its relation to the North Atlantic Oscillation

The omega equation method based on an equivalent isobaric geopotential height in sigma coordinates has been used to retrieve the precipitation over Greenland. 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 Greenland shows that the largest value in 1986 is 472 mm yr(-1) and the smallest value in 1995 is 309 mm yr(-1). The major interannual variability of the atmospheric circulation in the North Atlantic can be represented by the variation of the North Atlantic Oscillation (NAO) index, which is most pronounced during winter. It is found that if the NAO index increases, the total precipitation over Greenland decreases, and vice versa. The correlation coefficient between these two series for 1985-1995 is -0.75. The mean precipitation over southern Greenland, where the majority of precipitation falls, is more closely related to the NAO index in winter, and their correlation coefficient is -0.80. This relationship can be understood from the composite maps of sea level pressure and Greenland precipitation for the high and low index months. During months of high NAO index values, the Icelandic Low is strong. During months of low NAO index values, the monthly mean low is located to the southwest of Greenland over the Labrador Sea. Precipitation amounts 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 significant downward trends in annual precipitation from 1985-1995 for all of Greenland and its southern and central west coastal regions, amounting to about 3% per year.