Dynamic evolution of the 1997-1999 El Nino-La Nina cycle in the southern California Current System

The development of the strongest El Nino event on record in the equatorial Pacific in 1997-1998 and the rapid transition to strong La Nina conditions in 1998-1999 had a large impact on the physical and biological environment of the West Coast. We investigate the evolution of the physical structure and circulation dynamics of the southern California Current System (CCS) during this period based on hydrographic data collected on 25 cruises over a 45-month period (February 1996-October 1999). The El Nino period was characterized by a significant increase in dynamic height, extreme water mass characteristics, a strengthening and broadening of the poleward nearshore flow, and a temporary reversal of net alongshore transport. By early 1999, conditions in the CCS had reversed. The data suggest that remotely driven forcing (propagating oceanic waves) contributed to the anomalies observed during the El Nino period, while the cool-water conditions of 1999 were most likely a result of anomalous local atmospheric forcing. Published by Elsevier Science Ltd.