EVALUATION OF RECENT PRECIPITATION STUDIES FOR GREENLAND ICE-SHEET

The retrieval of an accurate spatial and temporal record of contempora ry Greenland precipitation is a uniquely challenging task because of t he extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales. A co mparison of precipitation data sets composed of monthly mean values fr om recent studies shows a convergence on the general features of the l ong-term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of Greenland. There is genera l agreement on a long-term Greenland average of about 35 cm yr(-1) and on long-term values for regional scales, although-differences for out lying data sets exceed 50% of the observed glaciological estimate for particular regions. A fundamental problem is the inadequate topographi c representation of Greenland in the numerical analyses. Nearly all of the data sets are overly dry for high-elevation areas, as seen from c omparisons with glaciological observations from Summit. The east-centr al region of Greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyse s. In contrast, there is strong agreement among all methods on the tem poral variability for the west-central region over a 15-year period. F rom the comparison it is concluded that none of the data sets is able to capture all of the regional-scale features. In general, however, th e deficiencies of each data set are readily identifiable from comparis on and evaluation in the context of circulation features. Agreement am ong the methods on particular regions and timescales gives increased c onfidence in drawing conclusions related to aspects of Greenland's pre cipitation climatology. In particular, an enhanced precipitation retri eval method is found to be less susceptible to data artifacts than oth er methods using operational analyses. In the north, anomalously high precipitation is associated with cyclonic development near the Fram St rait. For west-central Greenland the close agreement among methods is related to the dominant contribution of the mean circulation.