NOAA Environmental Technology Laboratory
PACJET 2001: PACIFIC LANDFALLING JETS EXPERIMENT
U.S West Coast Phase I: January - February 2001
Phase II: January - February 2002
S-band Radar
A new S-band vertical profiler with a coupler option for extending the dynamic range of the radar's receiver has been developed by the NOAA Environmental Technology Laboratory and successfully field tested during CALJET. The 30 dB of added dynamic range provided by the coupler allows the profiler to record radar reflectivity measurements in moderate-to-heavy precipitation that otherwise would not have been possible with this system because of receiver saturation. The radar hardware, signal processor, and operating software are based on existing S-band and UHF profiler technology developed at the NOAA Aeronomy Laboratory. Results from a side-by-side comparison with the NOAA K-band radar were used to determine the calibration and sensitivity of the S-band profiler. In a typical cloud profiling mode of operation, the sensitivity is -14 dBZ at 10 km or -25 dBZ at 3 km. During CALJET, the profiler was deployed at Cazadero, California, near the crest of the coastal mountains in a region climatologically prone to flooding. The profiler was part of an integrated observing system designed for measuring physical processes associated with orographic precipitation enhancement. The CALJET S-band dataset is also being applied to the problem of quantitative precipitation estimation using the WSR-88D (NEXRAD) network.


Time-height cross section of radar reflectivity (dBZ) measured with the vertically pointing NOAA/ETL S-band (3 GHz) radar near Cazadero, CA (CZD) on 5-6 February 1998. This radar includes a unique hardware option that allows for reflectivity measurements both in heavy precipitation and in cloud. Roman numerals classify periods of nearly constant rainfall rate determined by a rain gauge collocated with the radar. The inset shows the reflectivity-rain rate (Z-R) relationships calculated for eachobservation period along with the Z-R relationship for a Marshall-Palmer drop-size distribution(Z = 200R1.6). Combining this information with observations of the mesoscale wind field (notshown) provided by the CALJET wind profiler array suggests that upslope flow enhanced orographic rainfall during this storm by increasing the number of small drops at low altitudes, thus making the Marshall-Palmer relationship underestimate the precipitation rate.

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