[Seminar on Oct 15] Processes Shaping the Spatial Pattern and Seasonality of Surface Air Temperature Changes in Response to the Anthropogenic Forcing
Dr. Fangxing Tian
Reading University, UK
Room 1118, New Building, IAP
10am, Oct 15, 2018
In the second half of the 20th century, the land surface air temperature (SAT) warms more rapidly over some regions than the global mean. To understand the physical processes, and the roles of different components of anthropogenic forcing, in the decadal SAT warming over different regions, we have performed a set of time-slice experiments using MetUM-GOML1.
The results indicate a predominant role anthropogenic forcing in observed decadal SAT changes. In western Europe, SAT warming is stronger in JJA because the recent decadal decrease in AA emissions over Europe induces a substantial increase of clear sky short wave radiation, which warms local SAT strongly in JJA. Over central and eastern Eurasia, the GHG induced warming is stronger in DJF because the SAT warming reduces the snow depth and decreases the surface albedo at mid-latitudes, which increases the net surface shortwave radiation and in turn amplifies the SAT warming. Over Alaska, both GHG and AA forcing changes lead to strong warming in DJF by changing large scale circulations. The GHG and AA forcing changes lead to an El Ni？o-like SST anomalies and enhance Aleutian low, which increases the water vapor transport from North Pacific to Alaska and generates more cloud there. Thus, it is the enhanced local water vapor feedback and increased longwave cloud radiative effect that amplify the SAT warming.