On using the relationship between Doppler velocity and radar reflectivity to identify microphysical processes in midlatitudinal ice clouds

Abstract

Ground-based 35 GHz profiling Doppler cloud radar observations of ice clouds were used to derive the power law relation between Doppler velocity Vd and radar reflectivity Z (Vd = aZb). By removing the vertical air motion from Vd, the power law can be rewritten as Vt = aZb with Vt being the reflectivity-weighted particle terminal fall velocity. Profiles of this relation are variable with height. An attempt was made to relate this variability to the dominant microphysical processes in different layers of the cloud. Based on that, the possibility of using profiles of the parameters a and b to distinguish different microphysical regimes was explored. The methodology was applied to long-term measurements (January 1997 to December 2010) at the Atmospheric Radiation Measurement site in the Southern Great Plains. Principal component analysis was used to determine the modes of the profiles that explain most of the observed variance in the observations. Profile-averaged means and standard deviations of parameters a and b amounted to 0.65 ± 0.42 and 0.03 ± 0.19, respectively. Furthermore, three commonly used microphysical relations related to bulk quantities were used to determine values of a and b. These results were found to compare reasonably well with the values obtained from the radar observations. Finally, microphysical considerations showed that radar-derived values of parameter b can be explained in terms of particle size distribution moment changes. Key Points Climatology of profiles of cloud radar observables in ice clouds is made Microphysics is examined by profiles of Doppler velocity-reflectivity relation ©2013. American Geophysical Union. All Rights Reserved.