Influence of Basic Flow and Boundary Layer Top for a Low-Latitude Numerical Model

The influence of the background flow and the boundary layer top parameterization error on the low-frequency oscillation of the tropical atmosphere is discussed using a simple three-dimensional numerical model including a wave-CISK mechanism. The results show that the velocity of horizontal background flow (U) has an important impact on the frequency of low-frequency oscillation. When the horizontal wind U =2 m/s, the oscillation period reduces from 50-60 days to 30 days, while when U =-1 m/s the oscillation period increases to 70 days. Because the original oscillation moves eastward, a westerly flow can increase the oscillation while an easterly flow can restrain the oscillation and thus increase the oscillation period. Moreover, the low-frequency oscillation appears to be sensitive to the parameterization error in the model. When the selected value of the boundary layer is larger (1070 m) than the standard value (1030 m), the feedback of heat forcing is large. Thus, the oscillation moves faster than the standard speed and stops moving and increases toward infinity when the wave reaches 80°-90°E. On the contrary, when the selected value of boundary layer is smaller (1000 m) than the standard value, the feedback of heat forcing is not sufficiently large to maintain the oscillation. Thus, the wave will disappear within 110°-120°E, and the period is less than standard.