Conceptual model for the dynamical impacts of orographic gravity wave drag over the Tibetan Plateau on the springtime persistent rainfall in East Asia. (IMAGE)
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The breaking of orographic gravity waves induces a zonal wave drag in the middle troposphere, which destroys the geostrophic balance of the large-scale westerly flow and thus drives an ageostrophic meridional circulation across the Tibetan Plateau. The rising branch of the meridional circulation acts to lower the pressure and increase the meridional pressure gradient to the south of the Tibetan Plateau by dynamically pumping the lower-tropospheric air upwards. The southwesterly monsoonal flow on the southeastern flank of the Tibetan Plateau thus intensifies and transports more water vapor to East Asia, resulting in an enhancement of the springtime persistent rainfall.
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