Measurements of vertical velocities and divergence in the atmosphere using the MU radar in Japan

The accuracy of vertical velocity estimates obtained by Doppler radars is an important area of research. Many factors affect the estimates including beamwidth and wind field inhomogeneities. Typically, the radial velocity obtained from a vertically directed beam is assumed to represent the vertical velocity. By using two zenith angles, the extended velocity-azimuth display (EVAD) method can be used to account of divergence in the wind field, which must be present with a vertical velocity gradient. A unique experimental configuration using 17 beam directions has been implemented with the Middle and Upper (MU) Atmosphere radar in the summer of 1995. The EVAD technique was used to provide realistic estimates of vertical wind and divergence over the observation period and over a height range of 6-16 km. A comparison of vertical velocity estimates obtained from the vertical beam and the EVAD technique is presented for a case study of a typhoon passage in July, 1995. In addition, wind field divergence measurements are provided.