Impact of Ozone Valley over the Tibetan Plateau on the South Asian High in CAM5

Abstract

Local climate effects of Tibetan Plateau Ozone Valley (OVTP) were investigated by numerical simulations using Community Atmosphere Model version 5.1.1 (CAM5). After a 20-year spin-up period, two additional 10-year experiments were conducted. CAM5 was driven by monthly mean climatological ozone in control experiment (CE) and OVTP in the sensitivity experiment (SE) was removed from May to September. After the removal of OVTP, South Asian High (SAH) becomes more robust and colder from June to August, especially in June. The reason for enhancement of SAH is that removal of OVTP increasing ozone in 200–30 hPa leads to significant enhancement of longwave and shortwave radiative heating rate in SAH region in June, and then enhancement of horizontal divergence resulting from the radiative warming leads to strengthening of SAH influenced by the Coriolis force, while the colder SAH is primarily caused by dynamic processes. Adiabatic expansion and ascending movement mainly bring about temperature decrease in SAH after OVTP removal, but the thermodynamic process related to radiative heating offsets part of the cooling response.