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.

No abstract

No abstract

Wide‐ranging multi‐platform data from a major field campaign conducted over Indian region was used to estimate the energy absorbed in ten layers of the atmosphere. We found that during pre‐monsoon season, most of Indian region is characterized by elevated aerosol layers. Three‐fold increase in aerosol extinction coefficient was observed at higher atmospheric layers (>2 km) compared to that near the surface and a substantial fraction (as much as 50 to 70%) of aerosol optical depth was found contributed by aerosols above (reflecting) clouds. Consequent absorption and hence strong warming above clouds was found larger by several degrees (K) compared to that near the surface. The aerosol‐induced elevated warming was mostly confined below 2 km over northern Indian Ocean while found up to 4 km over central India, thus exhibiting strong meridional gradients (∼4 K) at atmospheric levels above 2 km. Climate implications of the large elevated warming are discussed.

[1] The influences of the springtime northern Indian biomass burning are shown for the first time over the central Himalayas by using three years (2007)(2008)(2009) . These biomass burning induced changes over the central Himalayan atmosphere during spring may also lead to enhanced short-wave absorption above clouds and might have an impact on the monsoonal rainfall.

SUMMARYChanges in the characteristics of atmospheric aerosol over a marine environment are investigated by making regular spectral extinction measurements in the visible and near-infrared region from a tiny island location, Minicoy (8.3'N, 73.W0E), situated in the Arabian Sea about 400 km due west of the southern tip of the Indian peninsula. The role of seasonally changing air-mass type in causing a regular annual variation in the spectral optical depths is delineated. The association between aerosol optical depths, surface wind speed and rainfall is examined. An increase in wind speed causes an increase in optical depths, the effect is predominant when a marine air m a s prevails. The impact of changes in wind speed on optical depths (due to sea-spray production over the sea) is parametrized in the case that the island is influenced by a marine air mass.Columnar size distributions, retrieved from the spectral optical depths, in general, show a bimodal lognormal distribution in the optically active size range. The accumulation mode is more sensitive to continental air-mass types, while the coarse mode is influenced by the marine conditions. The coarse mode is sharper but its position is variable. Increase in wind speed leads to a remarkable enhancement in the concentration and relative abundance of coarse particles, particularly during the monsoon season. The mass loading and effective radius are well associated and depend on wind speed histories. The findings are discussed.

[1] During an intense field campaign for generating a spatial composite of aerosol characteristics over peninsular India, collocated measurements of the mass concentration and size distribution of near-surface aerosols were made onboard instrumented vehicles along the road network during the dry, winter season (February-March) of 2004. The study regions covered coastal, industrial, urban, village, remote, semiarid, and vegetated forestlands. The results showed (1) comparatively high aerosol (mass) concentrations (exceeding 50 mg m À3 ), in general, along the coastal regions (east and west) and adjacent to urban locations, and (2) reduced mass concentration (<30 mg m À3) over the semiarid interior continental regions. Fine, accumulation-mode particles (<1 mm) contribute more than 50% to the total aerosol mass concentration in the coastal regions, which is more conspicuous along the east coast than the west coast, while the interior regions showed abundance (>50% of the total) of coarse-mode aerosols (>1 mm). The spatial composite of accumulation-mode share to the total aerosol mass concentration agreed very well with the monthly mean spatial composite of aerosol fine-mode fraction for February 2004, deduced from Moderate-Resolution Imaging Spectroradiometer data for the study region, while a point by point comparison yielded a linear association with a slope of 1.09 and correlation coefficient of 0.79 for 76 independent data pairs. Pockets of enhanced aerosol concentration were observed around the industrialized and urban centers along the coast as well as inland. Aerosol size distributions were parameterized using a power law. Spatial variation of the retrieved aerosol size index shows relatively high values (>4) along the coast compared to interior continental regions except at a few locations. Urban locations showed steeper size spectra than the remote locations.Citation: Moorthy, K. K., et al. (2005), Wintertime spatial characteristics of boundary layer aerosols over peninsular India,

No abstract