ZONALLY SYMMETRICAL EKMAN-CISK MECHANISM AND 30—60-DAY LOW FREQUENCY OSCILLATION NEAR THE EQUATOR^*

Based on the baroclinic semi-geostrophic model,the effects of zonally symmetrical Ekman-CISK mechanism on the characteristics of 30—60-day low frequency oscillation(LFO)near the equator are investigated.It is found that the theoretical results are in good agreement with the observational features of LFO.Besides,the planetary-scale LFO with the period of 30—60 d could be triggered by the Ekman-CISK mechanism,and the growth rate of perturbation with wave number 1 is in order of O (10-6s-1).The zonal propagation of LFO and the correspondinglong itudinal-height structure of physical quantities are also discussed in detail.