An improved method for determining the degree of snow crystal riming by vertical Doppler radar

An improved method is described to quantitatively determine the degree of snow crystal riming in stratiform precipitation using vertically pointing Doppler radar. Using this method, an automatic determination of the degree of riming at any height above the melting layer is possible. The quantitative statement of snow crystal riming with a limited uncertainty is obtained by a strict separation of stratiform and convective precipitation. For stratiform precipitation, the uncertainty of the degree of riming determined by this remote sensing technique typically remains below one unit on a six step riming scale with somewhat larger uncertainties for very weak riming. A criterion is given for when the situation is stratiform enough to use the proposed method for determining the degree of snow crystal riming. This method is usefull in all studies where direct crystal observation is not possible and the degree of riming is needed with good time resolution over a longer time period and in different altitudes.