Ice water content and reflectivity retrieval from cirrus clouds using millimeter-wave radar and in-situ ice crystal airborne data

Abstract

Data collected in March 2000 during the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Cloud Intensive operational period (Cloud IOP) at the Cloud and Radiation Testbed (CART) site in Lamont, Oklahoma was used to retrieve the equivalent reflectivity factor (Ze) and ice water content (IWC) of cirrus clouds. In situ measurements of ice particles were collected using the National Center for Atmospheric Research (NCAR) Video Ice Particle Sampler (VIPS), which flew on the University of North Dakota Citation research aircraft. Ground-based vertical radar profiles were collected using the University of Massachusetts (UMass) 33GHz/95GHz Cloud Profiler Radar System (CPRS). Data from both sensors (CPRS and VIPS) was used to retrieve and compare the equivalent radar reflectivity using density models that vary with respect to the dimensions of the particles, as well as a constant density of solid ice at 33 and 95 GHZ. The equivalent reflectivity that gave better agreement between instruments was the one that used the Brown and Francis [1995] density model. In addition, equivalent reflectivity was calculated with ice particles model of bullet shaped crystals developed with DDSCAT software and compared with the Mie (sphere shape) results. It was found that the effect of the shape was negligible at 33 GHz, but was significant at 95 GHz. Also, ice water content (IWC) was calculated for both sensors using variable density models for the ice crystals. IWC- Ze relationships for the three densities used in this investigation were obtained at 33 GHz. The IWC- Ze relationship obtained using Brown and Francis [1995] density, resulted the most reliable (the shape, and the low variability in the discrete values).