A water mass analysis of the 1991-1992 El Niño signal in the Farallon Islands region.
Hays, Kevin Austin Samuel
Ramp, Steven R.
Ramp, Steven R.
Collins, Curtis A.
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Five hydrographic (CTD) and acoustic Doppler current profiler (ADCP) cruises were conducted in February, May, August and late October/early November, 1991 and February, 1992 near the Farallon Islands off of central California in order to determine the seasonal variation of the circulation in the region. The timing of the study was such that the onset of the 1991-1992 El Nino/Southern Oscillation was directly observed in the data obtained. A detailed hydrographic analysis of the data showed single station temperature anomalies as great as 4.48 standard deviations warmer than the historical 40 year CalCOFI mean, and salinity anomalies 5.58 standard deviations fresher during February, 1992. The maximum anomalies for both temperature and salinity were between 100 - 150 m depth and within one Rossby radius (20 km) of the continental shelf break. A TS analysis suggested that there were no large intrusions of different water mass types, and that the anomalies resulted primarily from altered mixing processes due to thermocline/halocline depression. Strong positive sea level anomalies for the west coast of North and South America occurred simultaneously at the Equator and the far north (Gulf of Alaska) then spread from both directions towards central California. The broadening and strengthening of the Aleutian low caused onshore transport and downwelling at the Farallones site. Oceanic processes propagating northward may have occurred but could not be rigorously identified with this data set.
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