2-LAYER MODEL SIMULATIONS USING OBSERVATION AND MODEL-BASED WIND STRESSES OF THE 1985-1992 THERMOCLINE DEPTH ANOMALIES IN THE TROPICAL PACIFIC

A multivariate model testing procedure is used to investigate the ther mocline depth anomalies in the tropical Pacific during 1985-1992 simul ated by a two-layer model forced by five different surface wind stress fields. Two of these are derived from the pseudo wind stress produced from surface marine reports at the Florida State University (FSU), us ing a constant and a stability dependent drag coefficient. The others come from the response of three atmospheric general circulation models (ARPEGE, ECHAM3, and Hadley Centre) to the observed sea surface tempe rature. The simulations are compared to a new bimonthly analysis of th e 20 degrees C isotherm depth anomalies based on ship and moored buoy measurements. The best model-data fit is gained when the forcing uncer tainties are taken into account, considering the multiple simulations as representative of the latter. But they are still insufficient to ex plain the model-reality discrepancies. However, although the two-layer model has serious limitations in the eastern Pacific where the simula ted oceanic response is minimal while the observed variability is larg e, the testing procedure shows that; it reproduces the main features o f the observed variability and may thus be used to understand how, in a simulation, a particular feature of a forcing field translates. It i s found that the simulations based on the FSU product and the Hadley C entre wind stresses are comparable in realism, and are significantly m ore realistic than the ones based on the ARPEGE or ECHAM3 wind stresse s, because these misrepresent the phase of the 1986-1987 El Nino event . In addition, the ECHAM3 wind stress peaks off the equator, decreasin g the quality of the two-layer model response.