El Nino and La Nina - Equatorial Pacific thermocline depth and sea surfacetemperature anomalies, 1986-98

Simple models of the El Nino-Southern Oscillation (ENSO) phenomenon have pr ovided many of our basic ideas about ENSO mechanisms. These models exhibit a range of correlation patterns between thermocline depth anomaly (Z(20)A) and sea surface temperature anomaly (SSTA). We use 13 years of Pacific equa torial waveguide observations to explore the relationships between Z(20)A a nd SSTA. We find significant correlation in the eastern Pacific, and in the east-central Pacific when the east-central Pacific is normal or cooler tha n normal. We find no correlation in the western, west-central and east-cent ral (when warmer than normal) Pacific. It is inappropriate to attribute SST A changes to Z(20)A changes. Coupled ENSO models should be reexamined in li ght of these observed Z(20)A/SSTA relationships. Analysis of ocean general circulation models suggests that progress in understanding ENSO may depend as much on understanding SSTA/wind/near-surface current relationships and p rocesses, as upon thermocline change processes.