Observations of Winter Storms with a 2-D Video Disdrometer and Polarimetric Radar

During the Winter Icing and Storms Project 2004 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 the parameterization of winter precipitation in numerical forecast models.

The disdrometer provided 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 to develop methods for retrieving particle size distributions with radar. A capability to match radar-measured and disdrometer-based calculations of radar reflectivity factor and differential reflectivity is essential to retrieving hydrometeor characteristics with radar. 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 and computed values show agreement. Additionally, we retrieve particle size distributions from radar measurements and compare results to the disdrometer data. The combined dataset is then used to examine storm microphysical properties.