Ekman transport and pumping in the California Current based on the U.S. Navy's high-resolution atmospheric model (COAMPS)

Abstract

Upwelling in the California Current system due to Ekman transport and pumping was estimated using a high-resolution (9-km grid) atmospheric model reanalysis. Model winds, verified with satellite-measured winds at 13 locations, had weekly averaged wind components within 1.7 m s-1 RMS, and wind gradients within 1.6 m s-1 per 100 km RMS. Model wind hind-casts from May 1999 to September 2000 revealed narrow bands (about 10 by 50 km) of strong wind stress and wind stress curl parallel to the coast and adjacent to major coastal promontories. These bands, which are sub-grid scale in operational models, were capable of generating local upwelling greater than 10 m d-1 and downwelling greater than 5 m d-1. Peak summer estimates for the California Current system indicate vertical transport due to Ekman pumping was roughly 1.0 × 10-6 m3 s-1, and Ekman transport from alongshore wind stress was about 0.5 × 10-6 m3 s-1. These estimates suggest that Ekman pumping from wind stress curl is as important as Ekman transport from alongshore winds in the California Current system.