Variations of monsoon rainfall: A simple unified index

Abstract A new objective approach is proposed to identify the seasonal cycle of rainfall for major monsoon regions of the globe. Mean sea level pressure and low‐level zonal wind are combined to establish a standardized monsoon index. The index is able to determine the timing of the summer monsoon rainy season across all major monsoon regions in Asia‐Australia, Africa, and the Americas. A detailed application of the index in detecting the monsoon onset‐withdrawal phases is demonstrated for the Vietnam‐South China Sea region. A significant advantage of the index is that it can be used both for studies of monsoon rainfall variability and for monsoon predictability at seasonal time scales.