Evaluation of recent precipitation studies for Greenland Ice Sheet

Abstract

Abstract. The retrieval of an accurate spatial and temporal record of contemporary Greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales. A comparison 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 the numerical analyses. Nearly all of the data sets are overly dry for high-elevation areas, as seen from comparisons with glaciological observations from Summit. The east-central 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 west-central 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 timescales gives increased confidence in drawing conclusions related to aspects of Greenland's precipitation climatology. In particular, an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses. In the north, anomalously high precipitation is associated with cyclonic development near the Fram Strait. For west-central Greenland the close agreement among methods is related to the dominant contribution of the mean circulation.

Validation of ECMWF (re)analysis surface climate data, 1979–1998, for Greenland and implications for mass balance modelling of the ice sheet

“…Precipitation (validation data available only for DMI coastal sites) shows a 36% mean excess for ECMWF, which is exacerbated in the cases of stations 04231 and 04270 (Figure 7). Precipitation is predicted, rather than analysed, in the ECMWF models, so is less well constrained by observations and more sensitive to model flaws than temperature, although the ERA distribution seems good for Greenland (Bromwich et al, 1998). Of perhaps greater concern (especially as they constitute the 'ground truth' measurement), surface gauges -even the specialized Danish Hellmann type with protective Nipher shield widely used at Greenland synoptic stations (Table I(a)) -can be notoriously unreliable in the prevailing windy and snowy mountainous arctic environment.…”

Rapid Thinning of Parts of the Southern Greenland Ice Sheet

“…All three thickening zones are in regions of high s~iowfall (4); witli accumulation rates strongly linked to storm intensity and subject to considerable interanllual variability. However, model studies (4) conclude that precipitation over this region should have decreased significantly between 1985 and'1995, which would have resulted in thinning. In tlie northwest, where repeat radaraltimeter data (1) and compariso~i of snow ac-cumulatio~i with ice discharge (5) have shown previous tliinnmg, we observe a slight thickening.…”

Multiyear accumulation and temperature history near the North Greenland Ice Core Project site, north central Greenland

“…Polar accumulation estimates derived from the modeling of climate analysis data have the advantage of a synoptic view and explicit temporal control [Bromwich et al, 1998[Bromwich et al, , 1993]. Another advantage is that the risks of field data acquisition are effectively eliminated.…”

“…The accumulation output utilized here is derived from an evolving series of modeling efforts that have been extensively intercompared for Greenland [Bromwich et al, 1998] …”