OBSERVATIONS AND MODELING OF THE 1991-1992 EL-NINO SIGNAL OFF CENTRALCALIFORNIA

Five research cruises were conducted over the continental shelf and sl ope near the Farallon Islands, California, in February, May, August, a nd October/November 1991 and February 1992. The observations consisted of shipboard hydrographic and acoustic Doppler current profiler data and moored current meter measurements. Water mass anomalies were calcu lated for each cruise by subtracting seasonal means based on historica l data. In general, the maximum anomalies were observed subsurface in the 100-to 150-m range. In May 1991, equatorward, upwelling favorable winds elevated the thermocline resulting in cold, salty anomalies near shore, with cold, fresh anomalies offshore associated with the advecti on of Pacific Subarctic Water into the region from the north. Warm, fr esh anomalies and a strongly depressed thermocline were observed durin g the February 1992 cruise. A combination of coastal sea level and win d stress data and output from the Los Alamos National Laboratory paral lel ocean program model was used to explain the cause of these anomali es. The February 1992 anomalies were shown to be due to both the deepe ning of the Aleutian low in the North Pacific associated with the 1991 -1993 El Nino/Southern Oscillation event in the equatorial Pacific and poleward propagating intraseasonal coastal trapped Kelvin waves also arising from this event. The anomalous poleward wind forcing produced onshore flow, deepening of the thermocline, and downwelling at progres sively southward locations. The ''downwelling'' Kelvin waves propagate d northward with the two signals meeting somewhere near the cruise reg ion. Both the model and the coastal sea level data showed the phase sp eed of the waves to slow by about 50% after passing the Gulf of Califo rnia. This may be due to the scattering of energy from the fastest bar oclinic mode into a slower mode. The strongest wave signal in the equa torial Pacific did not necessarily produce the strongest anomalies off central California.