Observing structures vertical motions within stratiform clouds using a vertical pointing 94-GHz cloud radar

Cloud properties derived from a 94-GHz Doppler radar include the vertical distribution of liquid and ice water hydrometeors and a measure of their radial velocity relative to the radar. A temporal record of the vertical distribution of cloud particles can lead both to information on the vertical distribution of clouds and to the significant structures present within them. A time-space conversion method to derive the horizontal spatial scales of the observed dominant structures within stratiform clouds, such as cirrus, altostratus and stratocumulus, is considered. The method utilizes the Taylor transformation: the clouds that advect over the radar are assumed to be fixed in shape, and wind speeds derived from nearby wind profilers are used for the advecting cloud velocities. This method is shown to produce accurate retrievals even for significant uncertainties in the velocities of the profiler-derived wind speeds. It is applied to radar returns obtained from two different time periods when stratiform cirrus and altostratus clouds were present. The vertical motion of the cloud droplets derived from the radar during a case of cirrus uncinus clouds embedded in a cirrostratus layer lend support to a conceptual model of cirrus convection based on prior observations obtained from aircraft and centimeter-wavelength radar with lower temporal and vertical resolution. These applications of the radar are pertinent to validating models of micro- and mesoscale dynamics within stratiform clouds and are intended to be illustrative of the capabilities of a millimeter-wave Doppler radar. The analysis of large datasets in a statistical manner will ultimately lead to improved cloud parameterization schemes in general circulation models.