Integrated campaign for aerosols, gases and radiation budget (ICARB): An overview

During March-May 2006, an extensive, multi-institution, multi-instrument, and multi-platform integrated field experiment 'Integrated Campaign for Aerosols, gases and Radiation Budget' (ICARB) was carried out under the Geosphere Biosphere Programme of the Indian Space Research Organization (ISRO-GBP). The objective of this largest and most exhaustive field campaign, ever conducted in the Indian region, was to characterize the physico-chemical properties and radiative effects of atmospheric aerosols and trace gases over the Indian landmass and the adjoining oceanic regions of the Arabian Sea, northern Indian Ocean, and Bay of Bengal through intensive, simultaneous observations. A network of ground-based observatories (over the mainland and islands), a dedicated ship cruise over the oceanic regions using a fully equipped research vessel, the Sagar Kanya, and altitude profiling over selected regions using an instrumented aircraft and balloonsondes formed the three segments of this integrated experiment, which were carried out in tandem. This paper presents an overview of the ICARB field experiment, the database generated, and some of its interesting outcomes though these are preliminary in nature. The ICARB has revealed significant spatio-temporal heterogeneity in most of the aerosol characteristics both over land and ocean. Observed aerosol loading and optical depths were comparable to or in certain regions, a little lower than those reported in some of the earlier campaigns for these regions. The preliminary results indicate: • low (< 0.2) aerosol optical depths (AOD) over most part of the Arabian Sea, except two pockets; one off Mangalore and the other, less intense, in the central Arabian Sea at ∼18°N latitude; • High Ångström exponent in the southern Arabian Sea signifying steep AOD spectra and higher abundance of accumulation mode particles in the southern Arabian Sea and off Mangalore; • Remarkably low Ångström exponents signifying increased concentration of coarse mode aerosols and high columnax abundance in the northern Arabian Sea; • Altitude profiles from aircraft showed a steady BC level up to 3 km altitude with structures which were associated with inversions in the atmospheric boundaxy layer (ABL); • A surprisingly large increase in the BC mass fraction with altitude; • Presence of a convectively mixed layer extending up to about 1 km over the Arabian Sea and Bay of Bengal; • A spatial off shore extent of < 100 km for the anthropogenic impact at the coast; and • Advection of aerosols, through airmass trajectories, from west Asia and NW and regions of India leading to formation of elevated aerosol layers extending as far as 400 km off the east coast.