Vol 28, No 1 (1996)


Cover Page
Hydrometeor identification with polarization radar. NOAA/Environmental Technology Laboratory Ka-band (8.66 mm) radar RHI images from a winter snowstorm observed during the Winter Icing and Storms Project (2 km range rings, 2039 UTC 08 February 1994, Erie, Colorado). Reflectivity (top image) shows a vertical slice through a precipitating, -5 to + 11 dBZ convective cell, and an underlying -7 to -20 dBZ layer cloud. The corresponding elliptical depolarization ratio (EDR, bottom image) defines three distinct polarization regimes, one of the convective cloud, one for the layer cloud, and one where the hydrometeors from the two are mixing. In the layer cloud, EDR changes significantly (by 10 dB) from low elevation angles to zenith; this pattern and the depolarization values match theory for ice crystals of the thick plate growth habit. In the convective cell, EDR is invariant with elevation angle but larger in magnitude than a -14.8 dB value corresponding to spheres and drizzle; this signature corresponds to less-than-spherical graupel. These signatures were verified by samples of graupel that scavenged thick plates, taken at the ground in the zone of the mix (insert, sample from the NCAR microphysics van). See article by Reinking, Matrosov, and Bruintjes in this issue for applications to weather modification.
(Cover photo courtesy Roger Reinking, National Oceanic and Atmospheric Administration)