Spatial continuity of alpine precipitation

We use radar reflectivity to determine a set of typical variograms of Alpine precipitation, a summary statistic of spatial continuity. Variogram analyses benefit from the high resolution of reflectivity estimates in time and space. Spatial continuity of precipitation plays a key role in studying the representativity of point observations (gauge and disdrometer data, reflectivity profiles), and in distinguishing between stratiform and convective rain. Because of the direct influence of the orography on precipitation physics we expect a complex picture of variograms in the Alps. In fact, the variogram significantly varies in time and space, and so does the representativity. The error of a gauge-estimate for the average hourly rainfall in a drainage basin may be negligible in stratiform rain but serious in a meso-scale convective system. Further, the nugget variance of variograms is used to estimate the uncertainty of reflectivity measurements (e.g. caused by remaining signal fluctuation). For polar pixels we found nugget variances ranging from 0.3 to 1.9dB(2)(Z). (C) 2000 Elsevier Science Ltd. All rights reserved.