The westerly winds control the zonal migration of rainy season over the Tibetan Plateau

Abstract

Precipitation over the Tibetan Plateau is modulated by both the South Asian summer monsoon and the mid-latitude westerly winds. Using observations and numerical simulations, this study highlights the out-of-phase relationships between the mid-latitude westerly wind speeds and the west-east migration of Tibetan Plateau rainy season. When the westerly jet shifts northward before July, the weakening of westerly winds over the Tibetan Plateau leads to a westward shift of low-level warm air center and a westward extension of moist air convergence. Consequently, rainy season advances westward. Conversely, the southward shift of westerly jet after August leads to a strengthening of westerly winds and an eastward retreat of rainy season. Numerical simulations confirm the dominant role of mid-latitude westerly winds on the rain belt migration over the Tibetan Plateau, and further indicate that the timing of the westward extension of rain belt is determined by the weakening of mid-latitude westerly winds.