An Examination of the AGCM Simulated Surface Wind Stress and Low-Level Winds over the Tropical Pacific Ocean

The monthly mean surface wind stress and winds in the lower troposphere for 1986-92 simulated by the Center for Ocean-Land-Atmosphere Studies atmospheric general circulation model (AGCM) forced with observed sea surface temperature (SST) is compared with observations. It is found that the AGCM surface stress has weak equatorial easterlies during boreal spring and weak El Nin o-Southern Oscillation (ENSO) signals over the central and eastern Pacific Ocean. On the other hand, the AGCM winds at 850 mb are found to be in much better agreement with the observations. An empirical scheme is developed to reconstruct the AGCM surface wind stress, based on the AGCM winds from 850 mb. The reconstructed wind stress is more consistent with observations for both annual and interannual variability. A series of numerical experiments are conducted using the observed, AGCM, and reconstructed surface stress to force an ocean general circulation model. The results demonstrate that the low-frequency ENSO signals are significantly improved in the OGCM when the reconstructed dataset replaces the original AGCM stress. Improvements are evident in more realistic SST anomalies and variability of the thermocline depth.