EL-NINO SOUTHERN OSCILLATION-RELATED OCEAN-ATMOSPHERE COUPLING IN THEWESTERN EQUATORIAL PACIFIC

Using 43 years of Comprehensive Ocean-Atmosphere Data: Set and related data for the period 1950-1992, an examination is made into the region al dependence of ocean-atmosphere coupling in relation to the El Nino- Southern Oscillation (ENSO). The cross correlation between sea surface temperature (SST) and sea level pressure (SLP) anomalies over the glo bal tropics shows two patterns of significant negative correlation con sistent with a local hydrostatic response of SLP to SST: (1) the easte rn Pacific, where the correlation is symmetric about and largest on th e equator, and (2) the western Pacific, where symmetric regions of-neg ative correlation are found off the equator, separated by a region of positive correlation on the equator. Anomalies within these two patter ns vary out of phase with each other. While the SLP anomalies on both sides of the basin are of similar magnitude, the SST anomalies in the east are much larger than those in the west. Despite this disparity in the SST anomaly magnitudes between the eastern and western Pacific we argue that the ocean-atmosphere couplings in the western and west-cen tral Pacific are important for ENSO. The off-equator SST anomalies in the west enhance the SLP anomalies there, and they appear to initiate easterly wind anomalies over the far western Pacific during the peak E l Nino phase of ENSO. As these easterlies evolve, their effect upon th e ocean tends to oppose that of the westerly wind anomalies found over the west-central Pacific. These competing effects suggest a mechanism that may contribute to coupled ocean-atmosphere system oscillations. The west-central equatorial Pacific (the region separating the eastern and western patterns), while exhibiting large momentum and heat flux exchanges, shows minimum correlation between SST and SLP. Thus neither the SST and SLP anomaly magnitudes nor the correlation between them i s alone indicative of ocean-atmosphere coupling, and the regional depe ndence for such coupling in relation to ENSO appears to be more compli cated than mechanistic interpretations of ENSO would suggest.