New evidence for CH4 enhancement at upper troposphere associated with Asian summer monsoon

The Asian Summer Monsoon (ASM) region is key region transporting air to the upper troposphere, significantly influencing the distribution and concentration of trace gases, including methane (CH₄), an important greenhouse gas. We investigate the seasonal enhancement of CH₄ in the upper troposphere over the ASM region, utilizing retrievals from the Atmospheric Infrared Sounder (AIRS), model simulations and in-situ measurements. Both AIRS data and model simulation reveal a substantial seasonal increase in CH₄ concentrations of up to 3%, aligning with the active monsoon period. Notably, the spatial distribution of the methane plume demonstrates a southwestward shift in the AIRS retrievals, in contrast to the model simulations which predict a broader enhancement, including a significant increase to the east. A cross-comparison with in-situ measurements, including AirCore measurements over Tibetan Plateau and airline sampling across the Asian summer monsoon anticyclone (ASMA), favors the enhancement represented by model simulation. Remarkable CH₄ enhancement over west Pacific is also evidenced by in-situ data and simulation as dynamical extension of ASMA. Our findings underscore the necessity for cautious interpretation of satellite-derived methane distributions and highlights the critical role of in-situ data in anchoring the assimilation of CH₄.