A GCM STUDY ON TROPICAL INTRASEASONAL OSCILLATION

The ability of a at mospheric general circulation model to simulate the tropical intraseasonal oscillation (ISO)(30-60 day) has been studied using the out put of global spectral model (ALGCM (R42L9)) of the Institute of Atmospheric Physics,Chinese Academy of Sciences,compared with the results from the daily-mean reanalyzes data from NCEP/NCAR for the year 1978-1989.The model displays an evident periodic signal of intraseasonal oscillation in tropical area.The basic moving character of tropical ISO is prominent,and the change in phase speed between eastern and western hemispheres is also well present,the simulation of east ward propagating is better than that of the westward propagating,it is better reproduced in winter and in spring than in summer and in autumn.Although most models underest imate the strength of the ISO,this model has better ability to simulate the strength of the tropical intraseasonal oscillation,especially a marked strong kinetic energy of ISO at 200 hPa.This model basically simulates horizontal structure of the wind of ISO with convergence in lower air anddi vergence in upper air.The vertical structure of the zonal wind is also well reproduced.Moreover observed results show that the representing of seasonal preference to form strong ISO in winter and in spring is related to ISO's interannual variability,but it is represented in this model with strong ISO in winter and summer and weak ISO in spring and autumn.The structure of some physical elements such as vertical velocity,divergence and specific humidity and the special distribution of ISO have also differences with these from NCEP reanalyzes data,which make it clear to develop this model to simulate the structure and special distribution of ISO.