32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Wednesday, 6 August 2003
Stratiform precipitation observed by airborne radar at 94 and 10 GHz
Lin Tian, GEST/Univ. of Maryland, Baltimore County, Greenbelt, MD; and G. M. Heymsfield and L. Li
Poster PDF (126.1 kB)
A new airborne Cloud Radar System (CRS) operating at 3-mm wavelength (94 GHz) flew on ER-2 for the first time along with a 3-cm wavelength (10 GHz) radar (EDOP) during CRYSTAL-FACE campaign in south Florida. The radar over flew convective, stratiform, and cirrus regions and provided a unique opportunity to examine clouds and precipitation.

The high sensitivity of CRS allows detection of clouds with a radar reflectivity as small as -30 dBZ. Observation of high cloud such as cirrus can be successfully conducted with mm wavelength radar without much concern of signal attenuation. However, deep stratus and cumulus clouds possibly reaching the precipitation stage bring significant attenuation to reflectivity. In the region of light rain where the observation from the dual-wavelength radar is available, the drop size distribution can be estimated.

A stratiform cloud with light precipitation from July 11, 2002 is examined. It shows the following: 1) High cloud observed at 94 GHz but not at 10 GHz; 2) Bright band appears at 10 GHz but not well defined at 94 GHz. A noticeable difference between the reflectivities at the two wavelength is a well defined radar reflectivity minimum so called "dark band" at 94 GHz just above the melting level; 3) Attenuation at 94 GHz is shown by the decrease of the reflectivity toward the surface and the signal is completely attenuated in relatively heavy precipitation; In light rain region, the CRS detects the surface with significant one-way attenuation up to 15 dB while the attenuation at 10 GHz is negligible; 4) The Doppler velocity at vertical incidence at 94 GHz is smaller than that at 10 GHz in rain and about the same as that at10 GHz in the ice region. The results of the drop size distribution calculated from the dual-wavelength observations will be presented at the conference.

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