Improved Estimates of the Vertical Structures of Rain Using Single Frequency Doppler Radars

Abstract

It is important to understand the statistical–physical structure of the rain in the vertical so that observations aloft can be translated meaningfully into what will occur at the surface. In order to achieve this understanding, it is necessary to gather high temporal and spatial resolution observations of rain in the vertical. This can be achieved by translating radar Doppler spectra into drop size distributions. A long-standing difficulty in using such measurements, however, is the problem of vertical air motion, which can shift the Doppler spectra and therefore significantly alter the deduced drop size distributions and integrated variables. In this work, we overcome this difficulty by requiring that the measured radar reflectivity and the calculated rainfall rates satisfy fundamental physical theory. As a consequence, the mean vertical airspeed can be estimated and removed. Application of this new approach is demonstrated using vertically pointing Doppler radar observations in weak convection. It is shown that the new approach produces what appear to be better estimates of the rainfall rates as well as estimates of the temporal and spatial regionally coherent updraft and downdrafts occurring in the precipitation. The technique is readily applicable to other radars, especially those operating at non-attenuating frequencies.