Role of Tibetan Plateau in Northern Drought induced by Changes in Subtropical Westerly Jet

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  • 1 Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China
  • 2 Collaborative Innovation Center for Western Ecological Safety, Lanzhou University, Lanzhou, 730000, China
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Abstract

The Tibetan Plateau (TP), the “Water Tower of Asia”, plays an important role in the water cycle. However, few studies have linked the TP’s water vapor supply with the climate over North China. In this study, we found that changes in the subtropical westerly jet (SWJ) dynamically induce drought in North China, and the TP plays an important role in this relationship. During July-August for the period of 1981-2019, the SWJ center between 75°E and 105°E obviously shifted northward at a rate of 0.04° per year. Correspondingly, the zonal winds in the southern subtropics were incredibly weakened, causing the outflow of water vapor from the TP to decrease dramatically. Combined with numerical simulations, we discovered that a reduction in water vapor transport from the TP can obviously decrease the precipitation over North China. Sensitivity experiments demonstrated that if the water vapor outflow from the eastern border of the TP decreases by 52.74%, the precipitation in North China will decrease by 12.69% due to a decrease in the local cloud fraction caused by a diminished water vapor content in the atmosphere. Therefore, although less water vapor transport occurs in the upper troposphere than in the lower troposphere, the impact of transport from the TP in the former on the downstream precipitation cannot be ignored.

Corresponding author: Yuzhi Liu, E-mail: liuyzh@lzu.edu.cn

Abstract

The Tibetan Plateau (TP), the “Water Tower of Asia”, plays an important role in the water cycle. However, few studies have linked the TP’s water vapor supply with the climate over North China. In this study, we found that changes in the subtropical westerly jet (SWJ) dynamically induce drought in North China, and the TP plays an important role in this relationship. During July-August for the period of 1981-2019, the SWJ center between 75°E and 105°E obviously shifted northward at a rate of 0.04° per year. Correspondingly, the zonal winds in the southern subtropics were incredibly weakened, causing the outflow of water vapor from the TP to decrease dramatically. Combined with numerical simulations, we discovered that a reduction in water vapor transport from the TP can obviously decrease the precipitation over North China. Sensitivity experiments demonstrated that if the water vapor outflow from the eastern border of the TP decreases by 52.74%, the precipitation in North China will decrease by 12.69% due to a decrease in the local cloud fraction caused by a diminished water vapor content in the atmosphere. Therefore, although less water vapor transport occurs in the upper troposphere than in the lower troposphere, the impact of transport from the TP in the former on the downstream precipitation cannot be ignored.

Corresponding author: Yuzhi Liu, E-mail: liuyzh@lzu.edu.cn
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