JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. C12, PAGES 22,089-22,101, DECEMBER 15, 1990 Oceanic Heat Content Variability in the Tropical Pacific During the 1982-1983 El Nifio SCOTT R. SPRINGER School of Oceanography, University of Washington, Seattle MICHAEL J. MCPHADEN NOAA Pacific Marine Environmental Laboratory, Seattle, Washington School of Oceanography, University of Washington, Seattle ANTONIO J. BUSALACCHI Laboratory for Oceans, NASA Goddard Space Flight Center, Greenbelt, Maryland Anomalous heat transport and storageduring the 1982-1983 E1 Nifio are investigated using a linear, multimode model forced by observedwinds. Heat transport is decomposed into symmetric (about the equator) and antisymmetriccomponents. The former was dominatedby anomalous northward Ekman transport which represented an enhancement of the usual seasonalcycle. The latter involved both Ekman and geostrophictransports. Near-equatorial wind anomalies forced Kelvin and Rossby waves usually associatedwith E1 Nifio; together these waves set up antisymmetric, geostrophic transport which tended to opposedirect Ekman transport. Becausethe oppositionwas imperfect, there was net heat convergence which caused variationsin heat content in bandsof latitude centered on the equator. Within a fairly narrow band (---5 ø) heat content was anomalously high preceding E1 Nifio and was depleted following the event. Equatorial heat content anomalies were largely compensated by opposing anomalies in low latitudes of the extraequatorial ocean so that variability over broader bands of latitude about the equator was relatively small. A sampling study employing the model suggests that observational evidence for a heat content variations over the region - 15 ø is an artifact arising from inadequate spatial resolution offered by the sea level measurement network. 1. INTRODUCTION According to linear theory, abrupt changes in equatorial winds force packets of eastward propagating equatorial Kelvin waves and westward propagatinglong Rossby waves [Cane and Sarachik, 1976; McCreary, 1977]. In responseto a patch of westerly wind anomalies, the Rossby wave front is horizontally divergent near the equator, raising the ther- mocline in the west, and the equatorial Kelvin wave front is zonally convergent, depressing the thermocline in the east. The two wave fronts are connected by an eastward equato- rial jet, which zonally redistributes mass above the thermo- cline. These equatorial waves provide a mechanism by which wind anomalies in the central Pacific associated with the Southern Oscillation (SO) can effect the increase in sea level observed in the eastern Pacific during E1 Nifio (EN) and the simultaneous decrease in sea level in the western equa- torial Pacific [Wyrtki, 1984]. Linear wave models driven by observed winds have been quite successful in hindcasting ENSO-related sea level anomalies along the equator [Busa- lacchi and O'Brien, 1981; Busalacchi et al. 1983; Cane, 1984; Busalacchi and Cane, 1985; Pazan et al., 1986]. In the presence of meridional boundaries, equatorial waves also produce a meridional mass redistribution. A convergentequatorial Kelvin wave impinging on an eastern boundary is reflected to convergentlong Rossby waves and Copyright 1990 by the American GeophysicalUnion. Paper number 90JC01855. 0148-0227/90/90JC-01855505.00 coastal Kelvin waves [Moore and Philander, 1977], which together spread positive sea level anomalies symmetrically (about the equator) along the coastline. At extraequatorial latitudes (lyl > 5 ø) the zonal pressure gradient associated with the Rossby wave front drives meridional geostrophic transports, which are poleward in both hemispheres because of the antisymmetry of the Coriolis parameter. Conversely, when convergent extraequatorial Rossby waves have prop- agated across the basin to the western boundary, they are reflected as an equatorward, geostrophicboundary current. If the symmetric component of the westerly wind anomalies , extends beyond the equatorial region, the resulting antisym- metric Ekman drift is also equatorward. Sinceboth Ekman and geostrophic transports are antisym- metric about the equator, they cause divergences and con- vergences of mass in bands of latitude centered on the equator. In the steady state there can be no net convergence or divergence, so antisymmetric geostrophic and Ekman transports, when zonally integrated across the basin, must be of equal magnitude but opposite sign. This balance does not generally hold for time dependent problems, however, becausetime scales required to set up the geostrophic and Ekman transports are very different. Ekman transports are set up on inertial time scales, but the planetary wave processes which set up geostrophic transport require a minimum of 1 year for the first baroclinic mode in the Pacific [Cane and $arachik, 1977]. Until that time, there is net antisymmetric meridional mass transport. Consequently, after the abrupt changes in the symmetric component of 22,089