大气中40—60天低频振荡形成的数值试验

观测资料的分析表明,40—60天的低频振荡,除了在赤道附近有向东的传播外,在副热带和高纬度带还存在向西传播的现象.本文利用正压原始方程的谱模式,加以与运动(辐散)相联系的强迫(相当于加热场),模拟这类低频振荡发现有两类波存在:一类是周期约为10—20天向东传播的行星波,另一类是周期为40—60天向西传播的低频波,它是前一类行星波的波包相速度,每天5—6经度,纬向波数为1.这类低频波的出现可能是行星波与加热场非线性相互作用的结果. 这里之所以没有得到东传的40—60天的低频波,可能是由于模式格点较疏,使赤道Kelvin波不能明显激发出来.

Numerical Experiment on the Formation of 40-60 Day Low-FrequencyOscillation in the Atmosphere

By analysing the observation data, It is shown that besides eastward propogation in the equatorial area, the westward propogation of 40 - 60 day oscillation in the subtropical and high- latitude areas also exist. Uisng a barotropic primitive equation spectral model with a freeing (analogous to a heating field)which is changed with atmosphreic motion, this kind of oscillation is simulated. It is found that there are tow kinds of oscillations, i.e., 10 - 20 day planetary wave which propagates eastwards and 40-60 day low-requency wave which propagates westwards. This 40- 60 day low- frequency wave is a wave- packet of planetary waves and has a zonal wavenumber 1 structure with a phase speed 5-6 longitudes per day. This kind of low- frequency wave seems to be the results of the nonlinear interactions between the planetary wave and heating field.The reason that the eastward propagating 40 - 60 day oscillation can not be obtained here is that the model resolution is too low, and the Kelvin wave can not be correctly described.