Atmospheric diabatic heating–induced wave train from the Caspian Sea to South and East Asia during the summer monsoon season

摘要

During the summer monsoon season, the authors observe a wave train that stretches from the northern Arabian Peninsula and Caspian Sea to the Indo-Gangetic plains along the foothills of the Himalaya and extending further east of the Tibetan Plateau. The trend analysis between 1979 and 2018 with NCEP–NCAR reanalysis data show that the diabatic heating flux (averaged over 1000 to 500 hPa) tends to decrease significantly over the Caspian Sea and its surrounding regions. In addition, the sea level pressure is increasing by ~0.1 hPa yr~(?1) over the Caspian Sea, forming a high-pressure divergent center over there. The divergent center is collocated with an anticyclonic circulation trend at 850 hPa over the Caspian Sea. This decreasing diabatic heating flux modulates the local atmospheric circulation by increasing the surface pressure around the center of divergence, which further facilitates a wave train to propagate towards South and East Asia. This wave train transports the moisture fluxes at 925 hPa from the Caspian Sea, southeastward towards the South and East Asian monsoon region.