Showing papers by "Sathianeson Satheesh published in 2001"
Scripps Institution of Oceanography1, Max Planck Society2, Council of Scientific and Industrial Research3, Leibniz Association4, Indiana University5, Georgia Institute of Technology6, University of California, San Diego7, University of Hawaii at Manoa8, Oregon State University9, National Center for Atmospheric Research10, Met Office11, Goddard Space Flight Center12, Desert Research Institute13, Physical Research Laboratory14, Florida State University15, Urbana University16, Lawrence Berkeley National Laboratory17, Climate Monitoring and Diagnostics Laboratory18, University of Cambridge19, University of Miami20, Pacific Northwest National Laboratory21, Université Paris-Saclay22, University of Alaska Fairbanks23, National Oceanic and Atmospheric Administration24, Complutense University of Madrid25
TL;DR: The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing as discussed by the authors, and integrated the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one-and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects.
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 four-dimensional 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^(−2)) 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.
1,371 citations
10 Apr 2001
TL;DR: A cruise by ORV Sagar Kanya was conducted in the Arabian Sea and the Indian Ocean from 20 January to 12 March 1999 as discussed by the authors, where measurements on aerosol properties such as optical depth, mass concentration, size distribution, scattering and absorption coefficients were measured using instruments such as sun-photometer, quartz crystal microbalance, nephelometer and particle-soot absorption photometer.
Abstract: As part of the Indian Ocean Experiment (INDOEX) Intensive Field Phase (IFP), a cruise by ORV Sagar Kanya was conducted in the Arabian Sea and the Indian Ocean from 20 January to 12 March 1999. Measurements on aerosol properties such as optical depth, mass concentration, size distribution, scattering and absorption coefficients were measured using instruments such as sun-photometer, quartz crystal microbalance, nephelometer and particle-soot absorption photometer. One of the important findings is the large north-south asymmetry in the aerosol characteristics. Aerosol optical depth values were very high, exceeding 0.4, close to the west coast of India and the Arabian Sea, which is greater than by a factor of 4 or more, compared to the values south of the ITCZ. The wavelength exponent α, is found to be in the range of 1.3 to 1.7 in the high optical depth region and is in the range of 0.5 to 0.7 over the pristine region. Aerosol mass concentration data show that the nucleation mode aerosols (radius 3 . Correlating the aerosol mass with the scattering coefficient, we get a scattering to mass concentration ratio of 2.27 m 2 /g, for the Arabian Sea region, which is in between the values reported by other workers, 3.3 m 2 /g for the continent and 1.67 m 2 /g for the marine regions, elsewhere in the world. The single scattering albedo, ω derived from the scattering and absorption data, is around 0.9 for aerosols found over the Arabian Sea, while near the coastal regions the values are as low as 0.8. Low ω and high optical depth found in the coastal region and Arabian Sea indicate large absorption by aerosols. The results undoubtedly show a large spatial difference in aerosol characteristics between north and south of the ITCZ which could lead to a large asymmetry in aerosol radiative forcing between the two regions.
44 citations
Journal Article•
TL;DR: In this paper, the results of the measurements of aerosol spectral optical depths made over the Bay of Bengal and compares them with those over the equatorial Indian Ocean and the Arabian Sea, on-board the oceanographic research vessel, Sagar Kanya during its cruise 161-B in March 2001.
Abstract: Comprehensive investigations during the last decade have clearly established that aerosols have a significant impact on the climate. No serious attempts were made to characterize the aerosols over the Bay of Bengal, despite its role in the regional climate system. This paper reports the results of the measurements of aerosol spectral optical depths made over the Bay of Bengal and compares them with those made over the equatorial Indian Ocean and the Arabian Sea, on-board the oceanographic research vessel, Sagar Kanya during its cruise 161-B in March 2001. The aerosol optical depth was found to decrease with distance from the coast with an exponential scale distance of apprx1000 km for visible wavelengths and apprx1600 km for near infra-red wavelengths. A significant dominance of small particle concentration near the coast is observed both over the Arabian Sea and the Bay of Bengal. The mean aerosol optical depth was higher over the Bay of Bengal compared to the Arabian Sea, at the shorter wavelengths. Over the equatorial Indian Ocean regions, aerosol optical depths were much lower compared to the Arabian Sea and the Bay of Bengal and showed lesser wavelength dependence. The relative dominance of small particles is more over the Bay of Bengal compared to the Arabian Sea. Back-trajectory analysis shows that during the cruise period, the Arabian Sea was mainly influenced by air masses from the countries lying northwest of India, the Bay of Bengal by air masses from the east coast of India and the equatorial Indian Ocean mostly by the west coast and central India. The observed features are compared with long-term climatology of aerosol optical depth observations from the east and west coast of India and an island station in the Arabian Sea.
42 citations