Relationships between Doppler spectral moments within large-scale cirro- and altostratus cloud fields observed by a ground-based 95-GHz cloud radar

In this study, data obtained from measurements with a ground-based vertical -pointing 95-GHz polarimetric cloud radar are analyzed. The investigations concentrate on the relationships between the Doppler spectral moments obser ved in different regions of nonprecipitating cirrostratus and altostratus d ecks connected with warm fronts approaching the radar site. In some of thes e cases, a remarkably well-defined relationship between the radar reflectiv ity and the spectral width is found. It is demonstrated how this relationsh ip can be used to obtain information on the size distributions and the fall speeds of the particles in the investigated cloud sections. It is found tha t if single parameters of the size distributions, for example, are paramete rized by a lognormal distribution, they cannot be determined with an accept able accuracy. However, at least the changes of these parameters, such as m ean particle diameter and particle concentration, with changing reflectivit y as well as the behavior of the corresponding particle fallspeeds, can be described with the help of empirical relations between the Doppler moments. A main result is that significant changes in reflectivity within a cloud s ection (e.g., of 10 dBZ(e)) must correspond with a change in the relation b etween particle size and fallspeed, most commonly described by empirical po wer laws, and, therefore, probably with changes in particle shapes. This ki nd of radar data analysis will help to come to a better understanding of th e microphysical and dynamical properties of the investigated cloud types, e specially if further information from simultaneous measurements with other remote sensors is available.