摘要
In this paper,a tropical atmospheric model of relevance to shorts-term climate variations(Wang and Li 1993)is util- ized for study of the development of Madden-Julian oscillation.The model contains an interactive process of boundary-layer Ekman convergence and precipitation heating.The model is solved by expanding dependent variables in terms of parabolic cylindrical functions in the meridional direction and truncating three meridional modes n=0,2,4 for equatorial symmetric solutions.The free wave solutions obtained under long-wave approximation are induced as a Kelvin wave and two Rossby waves.After considering the effect of boundary-layer dynamic process,the modified Kelvin wave becomes unstable in long-wave bands with a typical growth rate on an order of 10^(-6) s^(-1)and an eastward phase speed of 10 m s^(-1);the most unstable mode is wavenumber one.These theoretical results are consistent with the ob- served Madden-Julian oscillation in equatorial area.For the two modified Rossby waves,one with a smaller meridional scale(n=4)decays except for extra long-waves;the other with a larger meridional scale(n=2)grows in short-wave bands.This may be relevant to explaining the westward propagation of super cloud clusters in the Madden-Julian oscillation.The theory suggests that the boundary-layer dynamic process is an important mechanism in the develop- ment of the Madden-Julian oscillation.
In this paper,a tropical atmospheric model of relevance to shorts-term climate variations(Wang and Li 1993)is util- ized for study of the development of Madden-Julian oscillation.The model contains an interactive process of boundary-layer Ekman convergence and precipitation heating.The model is solved by expanding dependent variables in terms of parabolic cylindrical functions in the meridional direction and truncating three meridional modes n=0,2,4 for equatorial symmetric solutions.The free wave solutions obtained under long-wave approximation are induced as a Kelvin wave and two Rossby waves.After considering the effect of boundary-layer dynamic process,the modified Kelvin wave becomes unstable in long-wave bands with a typical growth rate on an order of 10^(-6) s^(-1)and an eastward phase speed of 10 m s^(-1);the most unstable mode is wavenumber one.These theoretical results are consistent with the ob- served Madden-Julian oscillation in equatorial area.For the two modified Rossby waves,one with a smaller meridional scale(n=4)decays except for extra long-waves;the other with a larger meridional scale(n=2)grows in short-wave bands.This may be relevant to explaining the westward propagation of super cloud clusters in the Madden-Julian oscillation.The theory suggests that the boundary-layer dynamic process is an important mechanism in the develop- ment of the Madden-Julian oscillation.
基金
This work is supported by the National Natural Science Foundation of China.
