Toward Improving Ice Water Content and Snow Rate Retrievals from Spaceborne Radars, Emphasizing Ku and Ka-Bands

Abstract:

This study uses a data set from either overflying aircraft or ground-based radars operating at Ku and Ka bands, combined with in-situ microphysical measurements to develop radar reflectivity (Z_e)-ice water content (IWC) and Z_e-snowfall rate (S) relationships that are suited for retrieval of snowfall rate from the GPM radars.

During GCPEX, the NASA DC-8 aircraft, carrying the JPL APR-2 KU and KA band radars overflew the UND Citation aircraft, making microphysical measurements in the ice clouds below. On two days, 19 and 28 January 2011, there are a total of almost 7000 1-sec colocations of the aircraft, where a collocation was defined as having a combination of a spatial separation of less than 3 km and a time separation of less than 10 minutes.

During the NASA GPM Mid-latitude Continental Convective Cloud Experiment (MC3E), the Citation aircraft made in-situ observations over Oklahoma in 2011. We evaluated the data from two types of collocations. First, there were two Citation spirals on 27 April 2011, over the NPOL radar. At the same time, the UHF-band KUZR radar was collecting data in a vertically-pointing mode. Also, the Ka band KAZR Doppler radar was operating in a zenith orientation. Reflectivities and Doppler velocities, without and with appreciable Mie-scattering effects of the hydrometers (for KUZR and KAZR, respectively), are thus available during the spirals. Also during MC3E, six deep convective clouds with a total of more than 5000 5-sec samples and a range of temperatures from -40 to 0C were sampled by the Citation at the same time that NEXRAD reflectivities were measured at about the same position.

These data allows us to evaluate various backscatter models and to develop multi-wavelength Z-IWC and Z-S relationships. We will present the results of this study.