Snowflake distribution characteristics from HVSD measurements

In this study we use a large dataset of snow measurements collected by a ground-based optical disdrometer Hydrometeor Velocity and Shape Detector (HVSD). Measurements were taken at the Centre for Atmospheric Research Experiments (CARE) during the winter 2005/2006 as part of the Canadian CloudSat/CALIPSO Validation Project (C3VP). The HVSD measurements provide particle size and its terminal fall speed for each interval. From these, the snowflake size distribution, as well as the velocity-size relationship, can be derived. In this study, the characteristics of the measured size distributions are investigated in order to develop quantitative relationship and parameterizations of snowflake size and their melted diameter, particularly with regard to the higher moments of the distribution that are important for the mass content, reflectivity and mass- and reflectivity-weighted fall speed calculations. Moreover, from the derived dimensional relations for fallspeed and effective area ratio for each snow event and the published relation between the Best and Reynolds numbers, an approximate relationship between snowflake fall speed, its density and its size is obtained. Using these relationships for an individual snowflake together with the PSD measurements as a function of time during each snow event, the time evolution of radar reflectivity and reflectivity-weighted velocity are calculated and compared with the data of the collocated vertically pointing X-band radar (VertiX).