A New Relationship between Mean Doppler Velocity and Differential Reflectivity

Abstract

A new relationship has been established linking the vertical mean Doppler velocity of raindrop spectra and the accompanying differential reflectivities. It is based upon the specific radar combination of a vertically pointing Doppler and a polarization radar scanning at low elevations, and was derived from consideration of two extensive disdrometer datasets containing 40 000 raindrop-size distributions. Following a detailed error analysis of the new relation, the discussion is directed towards its possible application and limitation. It is shown that under optimum conditions the velocity errors are as low as 0.3 m s?1. This results in Doppler radar-derived drop-size distributions having liquid-water contents with uncertainties of only about 40%. Compared to standard particle fall speed estimations of the Rogers' type, this means an improvement in accuracy of more than a factor of three. Although the new technique is not suitable for operational use, it can provide fresh quantitative insight into the vertical structure of the dynamics and the microphysical processes of precipitation.