P1.6
Process partitioning of rainfall enhanced by coastal orography
Allen B. White, CIRES/Univ. of Colorado, Boulder, CO; and F. M. Ralph, P. J. Neiman, D. A. Kingsmill, and P. O. G. Persson
During the California Land Falling Jets Experiment (CALJET), a vertically pointing S-band radar was deployed at a site 510 m above mean sea level near the crest of the coastal mountains northwest of Cazadero, California. The radar was located next to a 10-m meteorological tower that included a tipping bucket rain gauge. The extended dynamic range (~100 dB) of this radar makes it an ideal tool to quantify the wide range of radar reflectivity values associated with the powerful mid-latitude storms that strike the U. S. West Coast during each winter season. In particular, an analysis of the profiles of radar reflectivity and Doppler velocity recorded by the radar revealed three substantially different rainfall processes that contributed to the rainfall enhancement observed at this elevated site (greater than a factor of two compared to an upstream coastal location). These processes can be described briefly as: "warm" rain, in which a reflectivity bright band is not evident; "cold" rain, in which a bright band is clearly visible with nearly constant radar reflectivity beneath the melting layer; and "hybrid" rain, which also exhibits a bright band but with a substantial increase in reflectivity below the melting layer. A surprising feature of the warm rain was that it consistently occurred with lower reflectivity, by as much as 10 dB near the surface, than cold rain with nearly the same rain rate. An algorithm was developed that uses the information provided by the S-band radar data to partition the nearly 100 inches of seasonal rainfall measured by the rain gauge into the three process categories described above. This paper describes these rainfall processes in more detail and provides results of the partitioning algorithm to further our understanding of the underlying physical processes associated with orographic rainfall enhancement.
Poster Session 1, Winter Storms (Poster Session)
Monday, 15 January 2001, 1:00 PM-3:30 PM
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