[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.

[1] We present results from complimentary measurements of physical and optical properties of aerosols carried out at Delhi, as part of the Indian Space Research Organization Geosphere Biosphere Programme's Land Campaign II in December 2004. For the first time we unravel ground truth values of several radiatively important aerosol parameters such as their wavelength dependency in absorption, scattering behavior, singlescattering albedo, number size distribution, and vertical distribution in the atmosphere from this polluted megacity in south Asia. Interesting features are observed in the behavior of aerosol parameters under intermittent foggy, hazy, and clear-sky conditions prevalent during the campaign. All aerosol parameters exhibited a large distribution in their values, with variabilities being particularly higher on hazy and foggy days. The average clear-sky aerosol optical depth (AOD) value is 0.91 ± 0.48, which is higher than the AOD value reported for most other cities in India during this season of the year. Increases in AOD on hazy and foggy days are found to be spectrally nonuniform. The percentage increase in AOD at shorter wavelengths was higher on hazy days compared to clear days. Diurnally averaged BC mass concentration varied from a low of 15 mg/m 3 during clear days to a high of about 65 mg/m 3 on hazy days. The wavelength dependency of aerosol absorption shows signatures of the presence of a significant amount of absorbing aerosols produced from biofuel/biomass burning. Single-scattering albedo at 525 nm is found to vary between 0.6 and 0.8 with an average value of 0.68 for the entire period. Lidar observations reveal that during a fog event there is a subsidence of aerosols to an extremely dense and shallow atmospheric layer of less than 200 m height from the surface. The presence of an aerosol layer at elevated altitudes is also detected. All the results are combined and used for estimating aerosol radiative forcing using a discrete ordinate radiative transfer model. We find a large negative forcing at the surface level in the range of À40 to À86 W/m 2 , while forcing at the top of the atmosphere varied between À2 and +3 W/m 2 .Citation: Ganguly, D., A. Jayaraman, T. A. Rajesh, and H. Gadhavi (2006), Wintertime aerosol properties during foggy and nonfoggy days over urban center Delhi and their implications for shortwave radiative forcing,

[1] We present results on various physical and optical properties of aerosols measured over Ahmedabad, an urban location in western India, from 2002 to 2005 and discuss their seasonal and interannual variabilities. Aerosol parameters which have been studied include AOD spectra, aerosol mass concentration, size distribution, BC concentration, wavelength dependency in absorption, scattering coefficient, single scattering albedo and their vertical distribution in the atmosphere. All data have been classified in terms of four major seasons, namely, dry, premonsoon, monsoon and postmonsoon. AODs show an increasing trend over the first half of the year, and this is more consistent at higher wavelengths. Variation of Angstrom parameter a shows dominance of smaller size particles during dry and postmonsoon seasons while increase in coarser particle concentration during premonsoon and monsoon seasons. PM10 mass concentration varied from low values close to 40 mg/m 3 to highs of about 106 mg/m 3 . Size distribution patterns of near surface aerosols exhibited presence of three distinct modes, all of which could be fitted using three lognormal modes. Highest values of BC mass are obtained during postmonsoon (7.3 ± 3.7 mg/m 3 ) while lowest values are measured during monsoon season (1.5 ± 0.8 mg/m 3 ). Wavelength dependency of aerosol absorption shows signatures of presence of significant amount of absorbing aerosols produced from biofuel/biomass burning in the atmosphere. Single scattering albedo at 0.525 mm are found to be 0.73 ± 0.1, 0.84 ± 0.04, 0.81 ± 0.03 and 0.73 ± 0.08 during dry, premonsoon, monsoon and postmonsoon seasons, respectively. Vertical distributions of aerosol for dry and postmonsoon seasons are characterized by high values of extinction coefficients within first few hundred meters from the surface where we find a sharp decrease in the extinction values with increasing altitude. Vertical distribution of aerosols during monsoon season shows presence of a very thick and stable aerosol layer between 0.5 and 2.0 km, contributing significantly to the columnar AODs.Citation: Ganguly, D., A. Jayaraman, and H. Gadhavi (2006), Physical and optical properties of aerosols over an urban location in

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[1] Using a global climate model with fully predictive aerosol life cycle, we investigate the fast and slow responses of the South Asian monsoon system to anthropogenic aerosol forcing. Our results show that the feedbacks associated with sea surface temperature (SST) change caused by aerosols play a more important role than the aerosol's direct impact on radiation, clouds and land surface (rapid adjustments) in shaping the total equilibrium climate response of the monsoon system to aerosol forcing. Inhomogeneous SST cooling caused by anthropogenic aerosols eventually reduces the meridional tropospheric temperature gradient and the easterly shear of zonal winds over the region, slowing down the local Hadley cell circulation, decreasing the northward moisture transport, and causing a reduction in precipitation over South Asia. Although total responses in precipitation are closer to the slow responses in general, the fast component dominates over land areas north of 25 N. Our results also show an east-west asymmetry in the fast responses to anthropogenic aerosols causing increases in precipitation west of 80 E but decreases east of it. Citation: Ganguly, D., P. J. Rasch, H. Wang, and J. Yoon (2012), Fast and slow responses of the South Asian monsoon system to anthropogenic aerosols,