Role of Thermal Variations on MJO Precipitation and Propagation

The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in the tropics, with wide-ranging impacts on weather across the globe. In spite of intense research, numerous questions on the processes that lead to the evolution of rainfall remain. Previous research has shown that water vapor plays a central role in the maintenance and evolution of rainfall in the MJO. The role of temperature variations, however, remains less explored. In this study, we use a novel semi-empirical framework that relates tropical precipitation to lower-tropospheric buoyancy. Using this definition, the contributions of moisture and temperature to precipitation (buoyancy) can be calculated in a unified manner. In this study, ERA-Interim data is used to isolate rainfall anomalies that are due to moisture and temperature, respectively. It is found that moisture alone can explain many, if not most, of the observed features of the intraseasonal precipitation anomalies. The thermal contribution to the intraseasonal precipitation anomalies is smaller but non-negligible. It suppresses rainfall to the east of the region of maximum rainfall, and enhances it to the west. The results imply that temperature fluctuations may not only play a role in determining intraseasonal rainfall anomalies, but may also play a role in MJO evolution.