The statistical relationship between upslope flow and rainfall in California's coastal mountains: Observations during CALJET

• Published in: Monthly weather review 2002-06, Vol.130 (6), p.1468-1492
• Main Authors: NEIMAN, Paul J, RALPH, F. Martin, WHITE, A. B, KINGSMILL, D. E, PERSSON, P. O. G
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; Mountains; Water in the atmosphere (humidity, clouds, evaporation, precipitation)
• ISSN: 0027-0644; 1520-0493
• DOI: 10.1175/1520-0493(2002)130<1468:tsrbuf>2.0.co;2

The California Landfalling Jets Experiment (CALJET) was carried out during the winter of 1997/98, in part to study orographic rainfall in California's coastal mountains using coastal wind profilers. This observational study statistically links hourly rainfall rates observed by tipping-bucket rain gauges in California's quasi-linear coastal mountains to the hourly averaged upslope component of the flow measured by coastal wind profilers immediately upstream. Vertical profiles of the linear correlation coefficient of upslope flow versus rain rate are calculated on a case-by-case basis, for all cases containing a low-level jet (LLJ), and for the winter season of 1997/98. These correlation coefficient profiles show a direct relationship between the magnitude of the upslope flow impacting the coast and the magnitude of the rain rate in the downstream coastal mountains. Maximum correlation coefficients are as large as 0.94 in some individual cases, 0.75 for a composite of LLJ cases, and 0.70 for the winter season. Using three locations with differing coastal terrain characteristics, it is found that the layer of upslope flow that optimally modulates orographic rainfall is near mountaintop, that is, about 1 km above mean sea level for California's coastal ranges. (Author)