Observations of winter storms with 2-D video disdrometer and polarimetric radar

During the Winter Icing and Storms project 2004 (WISP04) storms were probed with a two-dimensional video disdrometer and S-band dual-polarization radar. The data were collected in support of ongoing activities to develop radar-based algorithms for classifying hydrometeor types, quantifying winter precipitation, and improving parameterizations of winter precipitation in numerical forecast models.

Disdrometers provide detailed information regarding hydrometeor size, number concentration, terminal velocity, and shape. The measurements are being used to model properties of winter precipitation and to verify radar-based designations of particle types and retrieved size distributions. Derived characteristics and their temperature dependencies are presented. A capability to match radar-measured and disdrometer calculations of radar reflectivity factor and differential reflectivity is essential to retrieving hydrometeor characteristics with radar. The ability to quantify rainfall and retrieve drop size distributions from polarimetric radar is well established, but the problem is complicated for winter storms by the need to know particle density. Here bulk snowflake density is estimated using an empirical relationship derived from disdrometer measurements of precipitation volume and rain gauge measurements of precipitation mass. Reflectivity and differential reflectivity as measured by radar and computed from disdrometer observations are compared. The measurements are then used to discriminate between rain and snow.