Abstract. Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one-and fourdimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (_+10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20 +_ 4 W m -t) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.

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We describe and show results from a series of field campaigns that used balloonborne instruments launched from India and Saudi Arabia during the summers 2014–17 to study the nature, formation, and impacts of the Asian Tropopause Aerosol Layer (ATAL). The campaign goals were to i) characterize the optical, physical, and chemical properties of the ATAL; ii) assess its impacts on water vapor and ozone; and iii) understand the role of convection in its formation. To address these objectives, we launched 68 balloons from four locations, one in Saudi Arabia and three in India, with payload weights ranging from 1.5 to 50 kg. We measured meteorological parameters; ozone; water vapor; and aerosol backscatter, concentration, volatility, and composition in the upper troposphere and lower stratosphere (UTLS) region. We found peaks in aerosol concentrations of up to 25 cm–3 for radii > 94 nm, associated with a scattering ratio at 940 nm of ∼1.9 near the cold-point tropopause. During medium-duration balloon flights near the tropopause, we collected aerosols and found, after offline ion chromatography analysis, the dominant presence of nitrate ions with a concentration of about 100 ng m–3. Deep convection was found to influence aerosol loadings 1 km above the cold-point tropopause. The Balloon Measurements of the Asian Tropopause Aerosol Layer (BATAL) project will continue for the next 3–4 years, and the results gathered will be used to formulate a future National Aeronautics and Space Administration–Indian Space Research Organisation (NASA–ISRO) airborne campaign with NASA high-altitude aircraft.

[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