Recent Trends in Transport of Surface Carbonaceous Aerosols to the Upper‐Troposphere‐Lower‐Stratosphere Linked to Expansion of the Asian Summer Monsoon Anticyclone

Abstract

Using Modern‐Era Retrospective analysis for Research and Applications Version‐2 (MERRA‐2) re‐analyses, we have examined recent trends (2000–2019) in transport of surface carbonaceous aerosols (CAs), that is, organic carbon and black carbon, to the upper troposphere and lower stratosphere (UTLS) during the Asian summer monsoon (ASM). We find a significant increased concentration of UTLS CA, linked to a linear trend in an expansion of the Asian Summer Monsoon Anticyclone (ASMA). Over core monsoon latitudes (25°–35°N), the trends in UTLS CA are enabled by increased upward transport from surface sources via an intensified monsoon meridional circulation, with increased latent heating over the southern Tibetan Plateau and foothill regions, enhanced by feedback processes associated with radiative heating by UTLS CA. In the extra‐tropics, increased UTLS CA stems primarily from an extended source of increased wildfire emissions over eastern Siberia and northern Asia, coincident with a large‐scale anomalous anticyclone with enhanced surface warming and drying near (80°–120°E, 55°–70°N). Here, CAs are transported upward from the surface to the ULS, likely by increased pyro‐convection associated with enhanced wildfires, and enter the tropical UTLS via increased equatorward transport on the eastern flanks of anomalous upper‐level anticyclones, coupled to the expanded ASMA. Overall, the increasing UTLS CA trends associated with expansion of the ASMA are consistent with a hydrostatic expansion of a warming troposphere, reflected in a rise in the tropical tropopause and consequential dynamical adjustments of the ASM subtropical jetstream, modulating the climate of the greater ASM region.

Divergent features of the upper-tropospheric carbonaceous aerosol layer: effects of atmospheric dynamics and pollution emissions in Asia, South America, and Africa

“…Aerosol and ozone products have proved very helpful in the study of global air pollution, from the troposphere to the stratosphere (Che et al 2019. Moreover, the tropopause aerosol layer phenomenon has been revealed by several studies utilizing MERRA2 reanalysis (Yuan et al 2019a, Lau and Kim 2022, Wu et al 2022b, Bresciani et al 2024. The MERRA2 has been employed to recognize CAs trend in the upper troposphere and lower stratosphere linked to the anticyclone, and the aerosol components including CAs, dust and sulfate have also been widely utilized to explore the formation, source, transport, and variability of tropopause aerosol layer with the validation of observation including CALIPSO and in-situ measurements (Yuan et al 2019a, Lau and Kim 2022, Wu et al 2022b.…”

“…Moreover, the tropopause aerosol layer phenomenon has been revealed by several studies utilizing MERRA2 reanalysis (Yuan et al 2019a, Lau and Kim 2022, Wu et al 2022b, Bresciani et al 2024. The MERRA2 has been employed to recognize CAs trend in the upper troposphere and lower stratosphere linked to the anticyclone, and the aerosol components including CAs, dust and sulfate have also been widely utilized to explore the formation, source, transport, and variability of tropopause aerosol layer with the validation of observation including CALIPSO and in-situ measurements (Yuan et al 2019a, Lau and Kim 2022, Wu et al 2022b. The vertical profiles of aerosol from MERRA2 have also been validated against CALIPSO satellite retrieval and insitu observation (Mahnke et al 2021) as shown in figure S1.…”

“…Specifically, local emissions and long-range transport by prevailing southwesterly winds lead to high concentrations of surface pollutants over South and East Asia (Neely et al 2014, Zhang et al 2019, Wu et al 2022b. During the Asian summer monsoon period, deep convection and strong updrafts occur, forcing surface pollutants to penetrate into the stratosphere (Bucci et al 2020, Lau andKim 2022). Anticyclonic circulation in the upper troposphere acts as a trap, causing the pollutants to accumulate over the Tibetan Plateau rather than spreading globally (Vernier et al 2011, Yuan et al 2019a.…”

“…As shown in figure 1(b), the forest and grassland over South America and Africa would emit large amount of CAs through wildfire burning, with the considerable anthropogenic emission for CAs over Asia. The CAs, as one of aerosol components, have been adopted to identify features of ATAL(Yuan et al 2019a, Lau andKim 2022). The presence of upper-tropospheric CAs, as indicated by multiple data from MERRA2 reanalysis, CMIP6 simulation, and OMPS/LP satellite retrieval (figures 2 and 3), indicates the occurrence of TCALs over Asia, South America, and Africa.…”