The Statistical Relationship between Upslope Flow and Rainfall in California's Coastal Mountains: Observations during CALJET

Abstract

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.