Modeled variations of precipitation over the Greenland Ice Sheet

Abstract

A parameterization of the synoptic activity at 500 hPa and a simple orographic scheme are used to model the spatial and temporal variations of precipitation over the Greenland Ice Sheet for 1963-88 from analyzed geopotential height fields. Model coefficients are fitted to observed accumulation data, primarily from the summit area of the ice sheet. All major spatial characteristics of the observed accumulation distribution are reproduced apart from the orographic accumulation maximum over the northwestern coastal slopes. A downward trend in simulated ice sheet precipitation over the 26 years is found. It matches the accumulation trends during this period from ice cores drilled in south-central Greenland. The lower tropospheric specific humidities at two south coastal radiosonde stations also decrease over this interval. A systematic shift away from Greenland and decrease in activity of the dominant storm track are found for relatively low precipitation periods as compared to relatively high precipitation periods. Superimposed on the declining simulated precipitation rate for the entire ice sheet is a pronounced 3-5-yr periodicity. -from Authors