S-band radar observations of coastal orographic rain

The NOAA Environmental Technology Laboratory (NOAA/ETL) has developed a small, portable, S-band (2875 MHz) Doppler radar with extended dynamic range for cloud and precipitation studies. During the winter of 1997-98, this radar was part of a suite of remote and in-situ sensors deployed at a site near Cazadero, California, in the climatologically flood-prone Russian River region, for the California Land-falling Jets Experiment (CALJET). During CALJET, we programmed the radar to alternate between three operating modes to obtain 96 dB of useable dynamic range.

This paper presents ongoing analyses using the CALJET S-band radar dataset and, in particular, describes an algorithm designed to partition the 829 half-hour periods when the rain rate exceeded 1 mm hr-1 to one of three bulk microphysical processes. A key result of this analysis indicates that warm rain contributed to 37 percent to the total rainfall (1841 mm) observed during the CALJET period Jan.-Mar., 1998 (snow was not observed locally at the surface, 510 m MSL, during this period). This result is significant because WSR-88D radars overshoot this often shallow type of rain. Imbedded within the algorithm is a simple scheme for bright-band detection based on the vertical profiles of reflectivity and Doppler velocity. We will report on the operational benefit of this scheme, which will be evaluated Jan.-Mar., 2001 using reflectivity and Doppler velocity data in near real time from two of the 915-MHz wind profilers deployed for the Pacific Land-falling Jets Experiment.