Climatological perspectives of air transport from atmospheric boundary layer to tropopause layer over Asian monsoon regions during boreal summer inferred from Lagrangian approach
The Asian Summer Monsoon (ASM) region has been recognized as a key\nregion that plays a vital role in troposphere-to-stratosphere transport\n(TST), which can significant impact the budget of global atmospheric\nconstituents and climate change. However, the details of transport\nfrom the boundary layer (BL) to tropopause layer (TL) over these\nregions, particularly from a climatological perspective, remain an\nissue of uncertainty. In this study, we present the climatological\nproperties of BL-to-TL transport over the ASM region during boreal\nsummer season (June-July-August) from 2001 to 2009. A comprehensive\ntracking analysis is conducted based on a large ensemble of TST-trajectories\ndeparting from the atmospheric BL and arriving at TL. Driven by the\nwinds fields from NCEP/NCAR Global Forecast System, all the TST-trajectories\nare selected from the high resolution datasets generated by the Lagrangian\nparticle transport model FLEXPART using a domain-filling technique.\nThree key atmospheric boundary layer sources for BL-to-TL transport\nare identified with their contributions: (i) 38% from the region\nbetween tropical Western Pacific region and South China Seas (WP)\n(ii) 21% from Bay of Bengal and South Asian subcontinent (BOB), and\n(iii) 12% from the Tibetan Plateau, which includes the South Slope\nof the Himalayas (TIB). Controlled by the different patterns of atmospheric\ncirculation, the air masses originated from these three source regions\nare transported along the different tracks into the TL. The spatial\ndistributions of three source regions keep similarly from year to\nyear. The timescales of transport from BL to TL by the large-scale\nascents r-range from 1 to 7 weeks contributing up to 60–70% of the\noverall TST, whereas the transport governed by the deep convection\novershooting become faster on a timescales of 1–2 days with the contributions\nof 20–30%. These results provide clear policy implications for the\ncontrol of very short lived substances, especially for the source\nregions over Indian subcontinent with increasing populations and\ndeveloping industries.