Potential impact of carbonaceous aerosol on the upper troposphere and lower stratosphere (UTLS) and precipitation during Asian summer monsoon in a global model simulation

摘要

Recent satellite observations show efficient vertical transport of Asianpollutants from the surface to the upper-level anticyclone by deep monsoonconvection. In this paper, we examine the transport of carbonaceous aerosols,including black carbon (BC) and organic carbon (OC), into the monsoonanticyclone using of ECHAM6-HAM, a global aerosol climate model. Further, weinvestigate impacts of enhanced (doubled) carbonaceous aerosol emissions onthe upper troposphere and lowerstratosphere (UTLS), underneath monsoon circulation and precipitation from sensitivitysimulations.The model simulation shows that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay ofBengal, southern slopes of the Himalayas and the South China Sea. Doubling ofemissions of both BC and OC aerosols over Southeast Asia(10° S–50° N, 65–155° E) shows that loftedaerosols produce significant warming (0.6–1 K) over the Tibetan Plateau(TP) near 400–200 hPa and instability in the middle/upper troposphere.These aerosols enhance radiative heating rates (0.02–0.03 K day) near the tropopause. The enhanced carbonaceousaerosols alter aerosol radiative forcing (RF) at the surface by−4.74 ± 1.42 W m, at the top of the atmosphere (TOA) by+0.37 ± 0.26 W m and in the atmosphere by+5.11 ± 0.83 W m over the TP and Indo-Gangetic Plain region(15–35° N, 80–110° E). Atmospheric warming increasesvertical velocities and thereby cloud ice in the upper troposphere. Aerosol induced anomalous warming over the TP facilitates the relative strengthening of the monsoon Hadley circulation and increases moisture inflow by strengthening thecross-equatorial monsoon jet. This increases precipitation amounts over India(1–4 mm day) and eastern China (0.2–2 mm day). Theseresults are significant at the 99 % confidence level.