On the Use of Meso-beta Profiles and Reflectivity Variograms to better Describe Precipitation in Complex Orography

Interpreting radar data in complex orography, both when generating user products as well as studying precipitation mechanisms, requires optimum combination of the available observations with the knowledge of the visibility. First, to improve precipitation measurements in the Alps we propose a robust profile-correction scheme based on profiles on a meso-beta scale. In space, we combine radar measurements from a 70km-radius cylinder centred over the radarsite. Integration in time is controlled by the pwe-function (precipitation-volume-weighted exponentially-decaying function). The time constant is of the order of 100min. This procedure continuously yields a statistically well-defined profile. The resulting improvement in terms of ground-level precipitation rates reflects that the meso-beta profile explains an important part of profile variation.

In a second step, we determine a set of typical Alpine reflectivity variograms describing the spatial continuity of precipitation. Data is from volume-scanning and vertically-pointing radars of the MAP field experiment. The variograms provide answers to many practical questions, such as: What spatial variation of precipitation rate do we find in Alpine catchments? What is the optimum scale for vertical reflectivity profiles in profile-correction schemes? To what accuracy can we estimate areal precipitation from point observations? Are there preferred regions for convection in Alpine precipitation? Where can we see the influence of the orography?