Substantial methane (CH₄) emissions in Asia are efficiently transported to the upper troposphere through the monsoon dynamical system, which forms a remarkable seasonal CH₄ enhancement in the upper troposphere. Using a chemical transport model GEOS-Chem driven by surface optimized CH₄ flux, the CH₄ enhancement over the Asian monsoon region is explored as a combined effect of the monsoon dynamical system and regionally increased emissions during late monsoon season. The spatial distributions of CH₄ at the upper troposphere show strong subseasonal variability, which is closely tied to the east-west oscillation of Asian monsoon anticyclone (AMA). Besides, the AMA patterns influence the vertical structure of methane. The AMA center around 80°E favors the upward transport from north India and Bangladesh while the AMA center around 105°E favors the source from southwest China transported to the upper troposphere. The AMA center over the Iranian Plateau suppresses the vertical transport and favors the horizontal redistribution. According to our model sensitivity study, the differences in the upper tropospheric CH₄ anomalies caused by large-scale circulation is 1-2 times of that caused by regional surface emissions. Our research highlights the complex interaction between monsoon dynamics and surface emissions to determine the upper tropospheric methane.

UTLS, Adian summer monsoon, methane