The MJO (Madden and Julian 1971, 1972) is the leading mode of intraseasonal variability of the tropical atmosphere. Its most basic feature consists of a planetary-scale, eastward-moving region of deep convections. The influence of the zonal background flow on the low-frequency oscillation of the tropical atmosphere is studied by applying a simple three-dimensional wave-CISK model. The results show that the zonal background flow (U) has an important impact on the frequency of low-frequency oscillation. When the zonal wind U = 2 m/s, the oscillation period reduces from 50–60 days to 30 days, while U = -1m/s the oscillation period increases to 70 days. The study has been published in Chinese Journal of Atmospheric Sciences, the lead author is Dr. Wang Pengfei and Huang Ronghui at CMSR and coauthors are Dr. Huang Ping at LASG and Gu Lei at Aviation Meteorological Center, Air Traffic Management Bureau, Civil Aviation Administration of China.

The model result also suggested that the low-frequency oscillation appears to be sensitive to the parameterization error in the model. When 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 boundary layer top 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.

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