A study of the upper ocean processes in the tropical Pacific Ocean using satellite data, in situ measurements, and numerical models

Surface heat fluxes in the western tropical Pacific Ocean (WTPO) are estimated by three different methods. The first two methods are a bulk formula and the one-dimensional, level 2.5, turbulence closure inverse mixed layer model. It is found that the inverse method has large variations in daily mean heat flux estimation while the derived longer time-averaged net heat flux can better match the bulk formula result. This is due to the high sensitivity of the estimated net heat flux to relatively small sea surface temperature (SST) errors in the input. The third method is by a proportional relationship between the net heat flux and the sea level change rate. The relation is only valid for a medium range such as a 5° latitude by 5° longitude box for a monthly cycle or for a certain location with a diurnal scale in a small horizontal advection region. Surface net heat fluxes are found to be small in the WTPO from all three methods.; The relationship between total westerly wind forcing (TWWF) and sea level height anomaly (SSHA) are examined using ERS-1, ERS-2, and NSCAT scatterometer wind data and TOPEX/Poseidon altimeter data. The fact that the SSHA in the eastern Pacific Ocean is highly correlated to the TWWF in the WTPO suggests that the equatorial Kelvin waves are remotely forced by the TWWF in the WTPO. The relationship between the Western Pacific Warm Pool (WPWP) related parameters and the TWWF are also analyzed using multichannel SST (MCSST) and Reynolds SST data. It is found that the WPWP area and the zonal component of the WPWP centroid could be used as El Niño indexes. The analysis also shows that the WPWP centroid movement has a common characteristic: It moves clockwise with the major axis facing southwest-northeastward during onset of a typical El Niño year while it moves counterclockwise with the major axis facing southeast-northwestward during other years. This can be explained by the westerly wind patterns and the associated seasonal meridional migration of the WPWP. The differences and similarities between the 1991–93 El Niño with the 1982–83 and 1986–87 events are also discussed.