ENSO Signals in Tropospheric Temperature Simulated by an AGCM GAMIL

Using reanalysis data as a benchmark, the authors evaluate the performance of an Atmospheric General Circulation Model (AGCM) named GAMIL (Grid-point Atmospheric Model of LASG, IAP). GAMIL is used to simulate the tropospheric temperature anomalies associated with the El Ni o-Southern Oscillation (ENSO) in boreal winters for the period 1980-99. The results show that the symmetrical components of temperature anomalies simulated by GAMIL closely resemble those in the reanalysis data in spatial patterns, especially in the Northern Hemisphere. The limitation of the model is that the simulated cold anomaly over South Asia is located to the east of the reanalysis. The observed temperature anomalies in the South Pacific and the high latitudes of the Southern Hemisphere are not evident in the simulation. The maximum value is 0.8 K smaller and the minimum value is -0.4 K smaller than the reanalysis. The difference between the simulation and the reanalysis is more evident in the regional features of the asymmetrical components of the temperature anomalies. Our results demonstrate that the previously discovered weak response of the GAMIL model to specified sea surface temperature forcing is dominated by the symmetric (asymmetric) component in the tropics (extra-tropics).