Atlantic Origin of Recent Decadal Trends in Meridional Thermal Gradient and Global Monsoon

Literature pointed out a systematic enhancement of global monsoon (GM) during these three decades. Observations show an increasing trend in GM rainfall particularly over the Northern Hemisphere since 1979, in contrast to long-term decreasing trend since the mid-20th century associated with anthropogenic aerosols emissions. Wang et al. (2013) pointed out that the recent sea surface temperature (SST) trends in the Pacific and Atlantic result in the decadal GM enhancement. However, respective roles of the basin-wide ocean temperature trends in the decadal GM trend were not fully understood. Here we conduct ocean mixed-layer temperature assimilation experiments to explore local and remote influence of the basin-scale sea water temperature on the GM trend. Following to Li et al. (2016), we examine results of 12-member partial assimilation runs in an atmosphere-ocean coupled general circulation model, CESM1. Results indicate that the Atlantic temperature assimilation run can reproduce large parts of the recent climate trends including the tropical IO warming, negative PDO, enhancement of GM through air-sea interactions and resultant changes in meridional thermal gradient. The results of this study suggest that the recent intensified GM except the Asian monsoon can largely be understood as Atlantic origin.