Regional Contribution of Anthropogenic Carbon Monoxide in the Asian Summer Monsoon Upper Troposphere and Lower Stratosphere

We study the regional contribution of anthropogenic carbon monoxide (CO) to the Asian summer monsoon upper troposphere and lower stratosphere (UTLS) by using a tagged CO, specified dynamics, model experiment. We find that in climatological mean, surface emission from South Asia (SAS) makes the largest contribution to the UTLS anthropogenic CO, followed by East Asia (EAS), with smaller contributions from other regions. Furthermore, for the UTLS CO, that is, emitted from EAS and SAS, the year-to-year variability is large, and there are years in which the contributions from EAS and SAS are comparable. Composite analysis is performed to understand the dynamical mechanism. For the transport of EAS CO, we find that enhanced convection over the western Pacific plays an important role in leading to more UTLS CO via reduced westerly and advection to the Pacific Ocean in the midtroposphere as well as intensified northeasterly and confinement in the UTLS.