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 p ointing Doppler radar. Using this method, an automatic determination o f the degree of riming at any height above the melting layer is possib le. The quantitative statement of snow crystal riming with a limited u ncertainty is obtained by a strict separation of stratiform and convec tive precipitation. For stratiform precipitation, the uncertainty of t he degree of riming determined by this remote sensing technique typica lly remains below one unit on a six step riming scale with somewhat la rger uncertainties for very weak riming. A criterion is given for when the situation is stratiform enough to use the proposed method for det ermining the degree of snow crystal riming. This method is usefull in all studies where direct crystal observation is not possible and the d egree of riming is needed with good time resolution over a longer time period and in different altitudes.