Co-sponsored by Harvard University Center for the Enviornement and the China Project at Harvard Paulson School of Engineering and Applied Sciences
"Long-term variability of the Afro-Asian summer monsoon and its possible causes: combined natural and anthropogenic effects"
The Afro-Asian summer monsoon is a zonally planetary-scale system, with a large-scale rainbelt covering Africa, South Asia and East Asia both in the past century (1901-2014) and in the last three decades (1979-2014). With concurrent retreat and advance of the Afro-Asia monsoon system in Africa and Asia, a southward shift of the main monsoon rainband has been observed since the 1960s. Since then, a recent inter-decadal abrupt change of the precipitation in these regions occurred in the late 1990s. The entire rainbelt of the Afro-Asia monsoon system is now advancing northward. The increasing precipitation can be synchronously detected over the Yellow River - Huaihe River valley in China and the Sahel in North Africa. The in-phase increase of precipitation in the Sahel and Yellow River - Huaihe River valley since the late 1990s is associated with the teleconnection pattern caused by the AMO.
At the same time, the warm AMO phase resulted in significant warming in the upper troposphere in North Africa and northern part of East Asia, respectively. Consequently, such warming contributed to intensification of the tropical easterly jet (TEJ) through increasing the meridional pressure gradient both in the entrance region (East Asian branch) and the exit region (African branch). The above results indicate that the Afro-Asian summer monsoon has assumed a consistent and holistic inter-decadal change.
Future projection of the Afro-Asian summer monsoon is made based on CMIP5 models with the major monsoon rainbelt located in more northern latitudes, which reflects enhanced anthropogenic effects on the Afro-Asian summer monsoon system.