[A-AS05] Large-scale moisture and organized cloud systems

[AAS05-P02] The relationship between Walker Circulation and Equatorial waves

* Ryoko Arai¹ (1.Ochanomizu University)

Keywords:Walker circulation, Equatorial waves, Atmospheric circulation

The Walker circulation is the most prominent tropical zonal circulation on a global scale, which is influenced by sea Surface temperature fluctuations at a time scale longer than the intraseasonal time scale. Previous studies have theoretically suggested that equatorial waves accelerate or decelerate the large-scale zonal flow of the upper troposphere in the tropics. Therefore, this study investigates the relationship between the Walker circulation and equatorial waves to identify which equatorial waves are dominant depending on the strength of the Walker circulation. By sorting the strength of the downward branch of the Walker Circulation above the western Indian Ocean, we make composite maps of outgoing longwave radiation. The results imply that prominent equatorial waves vary depending upon the seasonality. In boreal winter when the Walker circulation is strong, some signals presumably associated with mixed Rossby-gravity waves are hinted, whereas in boreal spring when the Walker circulation is weak, Kelvin wave-like features are exhibited. Interannual variability of the aforementioned relationship will also be discussed.