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 from\nthe boundary layer (BL) to tropopause layer (TL) over these regions,\nparticularly from a climatological perspective, remain an issue of\nuncertainty. In this study, we present the climatological properties of\nBL-to-TL transport over the ASM region during boreal summer season\n(June-July-August) from 2001 to 2009. A comprehensive tracking analysis\nis conducted based on a large ensemble of TST-trajectories departing\nfrom the atmospheric BL and arriving at TL. Driven by the winds fields\nfrom NCEP/NCAR Global Forecast System, all the TST-trajectories are\nselected 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 are\nidentified with their contributions: (i) 38% from the region between\ntropical Western Pacific region and South China Seas (WP) (ii) 21% from\nBay of Bengal and South Asian subcontinent (BOB), and (iii) 12% from\nthe Tibetan Plateau, which includes the South Slope of the Himalayas\n(TIB). Controlled by the different patterns of atmospheric circulation,\nthe air masses originated from these three source regions are\ntransported along the different tracks into the TL. The spatial\ndistributions of three source regions keep similarly from year to year.\nThe timescales of transport from BL to TL by the large-scale ascents\nr-range from 1 to 7 weeks contributing up to 60-70% of the overall TST,\nwhereas the transport governed by the deep convection overshooting\nbecome faster on a timescales of 1-2 days with the contributions of\n20-30%. These results provide clear policy implications for the control\nof very short lived substances, especially for the source regions over\nIndian subcontinent with increasing populations and developing\nindustries.