Extratropical modulation on Asian summer monsoon at precessional bands

Abstract

In a 46-kyrs' transient accelerated simulation with the NCAR Community Climate System Model version 3 (CCSM3), the increased July insolation at precessional bands causes a drastic summer warming in North Africa, the midlatitudes of Eurasia from surface to the upper troposphere, with a cooling troposphere in the Northwest Pacific (NWP), which intensifies the land-ocean thermal contrast between Eurasia and its adjacent oceans. Associated with the tropospheric temperature variations are a lower-tropospheric strengthened low-pressure system from North Africa to the mid-high latitudes of Eurasia and a lower-tropospheric strengthened high-pressure system over the NWP. Meanwhile, the strengthened southwesterly or southerly winds prevail over the Asian monsoon region, indicating a stronger Asian summer monsoon. Summer precipitation increases in tropical Africa, South Asia, and the mid-high latitudes of East Asia, with a decreased precipitation over South China and the NWP. This response of atmospheric circulation and monsoon precipitation to the precessional changes is explained in the context of the extratropical Asian-Pacific Oscillation. © 2012. American Geophysical Union.