Abstract
Abstract. Recent satellite observations show efficient vertical transport of Asian pollutants from the surface to the upper-level anticyclone by deep monsoon convection. In this paper, we examine the transport of carbonaceous aerosols, including black carbon (BC) and organic carbon (OC), into the monsoon anticyclone using of ECHAM6-HAM, a global aerosol climate model. Further, we investigate impacts of enhanced (doubled) carbonaceous aerosol emissions on the upper troposphere and lower stratosphere (UTLS), underneath monsoon circulation and precipitation from sensitivity simulations. The model simulation shows that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay of Bengal, southern slopes of the Himalayas and the South China Sea. Doubling of emissions of both BC and OC aerosols over Southeast Asia (10° S–50° N, 65–155° E) shows that lofted aerosols 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−1) near the tropopause. The enhanced carbonaceous aerosols alter aerosol radiative forcing (RF) at the surface by −4.74 ± 1.42 W m−2, at the top of the atmosphere (TOA) by +0.37 ± 0.26 W m−2 and in the atmosphere by +5.11 ± 0.83 W m−2 over the TP and Indo-Gangetic Plain region (15–35° N, 80–110° E). Atmospheric warming increases vertical 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 the cross-equatorial monsoon jet. This increases precipitation amounts over India (1–4 mm day−1) and eastern China (0.2–2 mm day−1). These results are significant at the 99 % confidence level.
Highlights
Southeast Asia (10◦ S–50◦ N, 65–155◦ E) is one of the fastest-growing regions in terms of population and economy, and it contributes significantly to the emission of global aerosol particles (Ramanathan and Crutzen, 2003; Lin et al, 2013)
We investigated impacts of enhanced Asian (65–155◦ E, 10◦ S–50◦ N) carbonaceous aerosols on the upper troposphere and lower stratosphere (UTLS), monsoon circulation and precipitation over India and China using a state-of-the-art aerosol–climate model
To validate the model simulations, we compare (1) a simulated black carbon (BC) vertical profile with observations from aircraft measurements at Guwahati (26◦11 N, 91◦44 E), India, during August–September 2009 and an Aethalometer launched on a balloon sonde at Hyderabad (78◦ E, 17◦ N) on 17 March 2010, (2) the seasonal mean of simulated cloud ice content with climatology of combined measurements from CloudSat and CALIPSO (2007–2010), and (3) simulated precipitation with climatology of Tropical Rainfall Measuring Mission (TRMM) observations (1997–2016)
Summary
Southeast Asia (10◦ S–50◦ N, 65–155◦ E) is one of the fastest-growing regions in terms of population and economy, and it contributes significantly to the emission of global aerosol particles (Ramanathan and Crutzen, 2003; Lin et al, 2013). It is important to study the impact of fast-growing Asian emission of carbonaceous aerosols on monsoon precipitation. There are a few studies reporting the impacts of carbonaceous aerosols on precipitation over India (Meehl et al, 2008; Wang et al, 2009; Ganguly et al, 2012) and China (Guo et al, 2013, 2015). Transport of carbonaceous aerosols from the boundary layer to upper troposphere and their impacts on the UTLS and connecting monsoon circulation are not explored in detail. In this study we address the question of the impact of rapidly growing Asian emissions of carbonaceous aerosols (BC and OC) on the thermal structure of the UTLS, monsoon transport processes and rainfall over India and China. 3. The impacts of enhanced carbonaceous aerosol emissions on the UTLS and monsoon precipitation are described, and conclusions are given in Sect.
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