The 5th Conference on Polar Meteorology and Oceanography

4.8
MODERN PRECIPITATION VARIABILITY OVER THE GREENLAND ICE SHEET

David H. Bromwich, Ohio State University, Columbus, OH; and R. I. Cullather, Q. S. Chen, and B. M. Csathó

Greenland precipitation is an important climate variable with significant relevance to a variety of research interests. An accurate depiction of the contemporary spatial and temporal variability is a uniquely challenging task however, due to the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales. A survey of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long-term spatial patterns, but substantial disagreement on the temporal variability both regionally and for all of Greenland. There is general agreement on a long-term Greenland average of about 35 cm yr-1, and on long-term values for regional scales, although differences for outlying data sets exceed 50% of the observed glaciological estimate for particular regions. A fundamental problem is the inadequate topographic representation of Greenland in atmospheic numerical analyses and models. Nearly all of the data sets are overly dry for high elevation areas, as seen from comparisons with glaciological observations from Summit. The central-east region of Greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses. In contrast, there is strong agreement among all methods on the temporal variability for the central-west region over a 15 year period. From the comparison it is concluded that none of the data sets is able to capture all of the regional-scale features. In general, however, the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features. Agreement among the methods on particular regions and time scales gives increased confidence in drawing conclusions related to aspects of Greenland’s precipitation climatology. In particular, the close agreement among methods for central-west Greenland strengthens confidence in findings of a precipitation relation with the North Atlantic Oscillation (NAO). Using an enhanced precipitation retrieval method, it is shown that if the NAO index increases, the mean total precipitation over Greenland decreases. The correlation coefficient between the two series for 1985-95 is (-) 0.75. The NAO index in winter is more closely related to the mean precipitation over southern Greenland where the majority of precipitation falls, and their correlation coefficient is (-) 0.80. The atmospheric circulation over the North Atlantic region is the primary control on snow accumulation in Greenland

The 5th Conference on Polar Meteorology and Oceanography