Climate response of the South Asian monsoon system to anthropogenic aerosols

Abstract

[1] The equilibrium climate response to the total effects (direct, indirect and semi-direct effects) of aerosols arising from anthropogenic and biomass burning emissions on the South Asian summer monsoon system is studied using a coupled atmosphere-slab ocean model. Our results suggest that anthropogenic and biomass burning aerosols generally induce a reduction in mean summer monsoon precipitation over most parts of the Indian subcontinent, strongest along the western coastline of the Indian peninsula and eastern Nepal region, but modest increases also occur over the north western part of the subcontinent. While most of the noted reduction in precipitation is triggered by increased emissions of aerosols from anthropogenic activities, modest increases in the north west are mostly associated with decreases in local emissions of aerosols from forest fire and grass fire sources. Anthropogenic aerosols from outside Asia also contribute to the overall reduction in precipitation but the dominant contribution comes from aerosol sources within Asia. Local emissions play a more important role in the total rainfall response to anthropogenic aerosol sources during the early monsoon period, whereas both local as well as remote emissions of aerosols play almost equally important roles during the later part of the monsoon period. While precipitation responses are primarily driven by local aerosol forcing, regional surface temperature changes over the region are strongly influenced by anthropogenic aerosols from sources further away (non-local changes). Changes in local anthropogenic organic and black carbon emissions by as much as a factor of two (preserving their ratio) produce the same basic signatures in the model's summer monsoon temperature and precipitation responses.

Worldwide impacts of climate change on energy for heating and cooling

“…Given the neglect of aerosol forcing in PLASIM-ENTS, this JJA cooling in south-east Asia should not be regarded as robust; aerosols are an important forcing of the south-east Asian monsoon through a range of likely competing effects (-see e.g. (Ganguly et al, 2012).…”

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

“…However, atmosphere-ocean coupled models often need multicentury simulations to take into account the slow response of SSTs (Danabasoglu and Gent, 2009). The coupled atmosphere slab ocean model by Ganguly et al (2012) shows a mix response of precipitation distribution on the climate scale. It shows a reduction in precipitation over the western coast line of the Indian peninsula and an increase over northwestern part of Indian subcontinent.…”

“…However, 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(Guo et al, , 2015. Since convective transport (during the monsoon season) inter-links tropospheric processes with the UTLS (Randel et al, 2010;Vogel et al, 2011Vogel et al, , 2015Fadnavis et al, 2013), it is essential to understand impacts of boundary layer emissions on the UTLS.…”

Investigation of the aerosol–cloud–rainfall association over the Indian summer monsoon region

“…This was done to avoid the inclusion of extreme orographic precipitation as well as retrieval error in the satellite products (e.g., lower sensitivity over brighter land surfaces for MODIS aerosol products). The ISMR has previously been extensively studied by several investigators (Bollasina et al, 2011;Goswami et al, 2006;Sengupta et al, 2013) as the rainfall variability over this re- gion is highly correlated with that of the entire Indian rainfall during June to September (Gadgil, 2003). Generally, aerosol loading over the ISMR is very high (climatological mean AOD of 0.56, Fig.…”

“…Lau and Kim (2006) have shown that an aerosol-induced atmospheric heating over Himalayan slopes and the Tibetan Plateau during the monsoon onset period intensifies the northward shift of the Indian summer monsoon, causing a reduction in rainfall over the Indian summer monsoon region (ISMR). On the other hand, a high aerosol loading also induces a solar dimming (absorbing) effect at the surface (Ramanathan and Carmichael, 2008;Ramanathan et al, 2001), which can alter the land-ocean thermal gradient and weaken the meridional circulation, resulting in a drying trend in seasonal rainfall during the Indian summer monsoon (Bollasina et al, 2011;Ganguly et al, 2012). The present of higher concentrations of absorbing aerosols over northern India is shown to induce a stronger northsouth temperature difference, which fosters an enhancement in moisture convergence from the ocean and a transition of a break spell of the Indian summer monsoon (ISM) into an active spell of ISM (Manoj et al, 2011).…”