Asian Climate and Its Variability in Association with Large-Scale Topography

Abstract:

The large-scale topography of the Tibetan Plateau (TP) and Iranian Plateau (IP) can affect the formation of the Asian climate pattern and its variability mainly through thermal forcing in spring and summer, and mechanical forcing in winter. The TP forcing in spring has significant impacts on the onset of the Asian summer monsoon (ASM) over the Bay of Bengal (BOB) by enhancing the BOB warm pool at the surface and by modulating the South Asian High (SAH) in the upper troposphere. Numerical simulations also demonstrate that the thermal effects of the Tibetan and Iranian Plateaus (TIP) are crucial for the formation of the East Asian and South Asian summer monsoons (SASM) because the surface sensible heating (SH) of the TIP is the major driver of the water vapor transport required for the genesis of the north branch of the SASM.

On intra-seasonal timescales, the TP thermal forcing significantly modulates spring rainfall in southern China and generates the bi-weekly oscillation of the SAH in summer. Despite the global climate warming, the atmospheric heat source over the TP, particularly the surface SH, exhibits a clear weakening trend from the 1980s to 2000s. This weakening of the surface SH contributes to the anomalous ‘dry in the north’ and ‘wet in the south’ rainfall pattern observed over East China. Activities for further understanding the mechanism of TP forcing on the multi-scale variability of the Asian climate are also discussed.