INTERACTION BETWEEN WAVES IN LOW-LATITUDE ATMOSPHERE AND TROPICAL LOW-FREQUENCY OSCILIATION

This paper is an attempt to reveal the dynamic mechanism of low-frequency oscillation(LFO) in tropical atmosphere. A two-level model on equatorial β-plane which includes the equation of water vapor evolution and the interaction between condensational latent heating due to convection and large-scale dynamic processes is developed. The difference in both heating capacity and moisture evaporation between underlying land and ocean surfaces is also taken into consideration. Firstly, the eigenmode in this model is analysed to reveal the effect of convective heating on equatorial waves. It is found that with this heating, all the waves including Kelvin waves, Rossby waves, gravity waves and mixed Rossby-gravity waves, are slowed down, thus frequency differences between fast and slow waves are reduced. Therefore these waves are more likely to interact with each other, causing the perturbations to propagate eastward very slowly and producing LFO. The comparison between results of dry and moist model integration has confirmed the conclusion from dynamic analysis.