Progress in Precipitation Growth Measurements.

摘要

Proper sampling of precipitating weather systems has always been difficult. The minute, infrequent direct particle sampling from rudimentary instrumentation has given only a snapshot of the particulate population. Broad coverage of the storm structure has been available from radar coverage, but conversion of the radar signal to the particulate population details, particularly in the case of snow and ice crystal clouds, has not been quantitative. New electro-optical devices now make it possible to gather copious data on particle distribution from aircraft. The results from measurements with the particulate probes developed by Knollenberg and flown in U.S. East Coast Cyclonic storms show how the particulate spectra change dramatically from narrow ice crystal spectra found at storm tops to broad snow spectra near the melting level. With the high powered SPANDAR radar at Wallops Island, Va. measurements of the radar reflectivity factor (Z) a short distance in front of the aircraft permitted comparison between two independent methods of obtaining Z. The analytical methods used are also described, including a discussion of the particular extrapolations used to adjust for the limited sample size of the airborne instruments as well as the equations used to convert from physical crystal size to particle mass.