Verification of S-Polka Ka Band Radar/Radiometer LWC and RES Retrievals with GRIDS Retrievals and Aircraft Measurements and Comparison to GOES Icing Products for the WISP04 10-11 March Event

Recent studies have shown the usefulness of employing a two-channel radiometer and a single radar band to derive liquid water content (LWC) and radar-estimated size (RES) fields. This study demonstrates the utility of this super-cooled liquid water (SLW) detection method by validating the retrieval results from a case study with in situ and remotely-sensed data.

An array of instrumentation platforms were operating from February through early April during the Winter Icing Storms Project 2004 (WISP04) near Boulder, Colorado. A Ka-band radar system (S-Polka) with a colocated 2-channel radiometer was located 21 km southwest of the NOAA Ka-band radar on the GRound-based Icing Detection System (GRIDS) with its own colocated 2-channel radiometer. A research aircraft with an LWC probe was flown in the radar domain during periods of winter weather. Icing products derived from the Geostationary Earth-Orbiting Satellite - West (GOES-W), such as liquid water path (LWP), cloud phase, effective particle size and cloud top and base heights were also available.

The current study compares retrieved LWC and RES from the S-Polka and GRIDS platforms to the airborne in situ probe and to products derived from GOES for the 10-11th of March WISP04 winter icing event. This upslope-induced event produced significant SLW aloft, with little precipitation at the surface. Results indicate that the LWC and RES radar/radiometer retrievals compare favorably to each other and to the airborne probe data. GOES LWP values were within +/-20% of the GRIDS LWP values through the early stages of the event. GOES icing products did not compare well to the radar/radiometer and in situ data later in the event, due to the shallow nature of the upslope-induced clouds and the proximity in time to sunset. This paper will describe the study results in greater detail.