Sea Surface Temperature, Geostrophic Current and Surface Heat Advection in the Western Tropical Pacific.

Sea surface temperature (SST), geostrophic current and surface heat advection in the western tropical Pacific Ocean during the period from October 1992 to September 1993 were computed using satellite and meteorological data. The SSTs were retrieved from NOAA-11 AVHRR data using a multichannel SST (MCSST) algorithm. Empirical orthogonal function (EOF) analysis was applied to analyze the major patterns and annual variability of the SST. For the temporal EOF modes, the zonal distribution of the SST overwhelmed all other variability with its strong seasonal pattern, while for the annual mean of the MCSSTs, the warm pool structure is the dominant pattern. The strength of the warm pool is dominated by the southern hemisphere seasonal cycle. Another important feature of the warm pool is that its boundaries seem related to the equatorial current system. To the north the boundary coincided with the north equatorial current, while to the south it was associated with the south equatorial current. The geostrophic current derived from TOPEX altimeter data referred to seasonal mean surfaces from hydrographic measurements. The changes in the quasi -monthly currents in the region of interest reflect both seasonal and non-seasonal changes. The effects of mesoscale circulations on the sea surface height contours and coincident buoy tracks are quite large and must be considered in any comparisons between the surface velocities in this region. The surface heat advections were computed using the SSTs and the geostrophic current data, as well as the Ekman drift estimated from meteorological monthly mean surface wind data. In general, meridional component of the geostrophic current dominates the heat advection pattern in most cases, and heat advection due to Ekman drift is usually small in amplitude and spatial variance both for the warm advection and the cold advection. An exception was near the equator at the eastern dateline where the SST had a cold tongue structure intruding from east to west in the northern hemisphere during fall and winter, and Ekman drift had a strong divergence effect at the equator. As a result, strong cold advection persisted in this area. The heat advection due to the Ekman drift is small in the total heat advection pattern, but this does not mean that it can be neglected in the total budget. In fact, it makes an important contribution to the area mean of the heat advection that is related to the area variance and centroid movement of the warm pool.