Abstract
Abstract. The information on altitude distribution of aerosols in the atmosphere is essential in assessing the impact of aerosol warming on thermal structure and stability of the atmosphere. In addition, aerosol altitude distribution is needed to address complex problems such as the radiative interaction of aerosols in the presence of clouds. With this objective, an extensive, multi-institutional and multi-platform field experiment (ICARB-Integrated Campaign for Aerosols, gases and Radiation Budget) was carried out under the Geosphere Biosphere Programme of the Indian Space Research Organization (ISRO-GBP) over continental India and adjoining oceans during March to May 2006. Here, we present airborne LIDAR measurements carried out over the east Coast of the India during the ICARB field campaign. An increase in aerosol extinction (scattering + absorption) was observed from the surface upwards with a maximum around 2 to 4 km. Aerosol extinction at higher atmospheric layers (>2 km) was two to three times larger compared to that of the surface. A large fraction (75–85%) of aerosol column optical depth was contributed by aerosols located above 1 km. The aerosol layer heights (defined in this paper as the height at which the gradient in extinction coefficient changes sign) showed a gradual decrease with an increase in the offshore distance. A large fraction (60–75%) of aerosol was found located above clouds indicating enhanced aerosol absorption above clouds. Our study implies that a detailed statistical evaluation of the temporal frequency and spatial extent of elevated aerosol layers is necessary to assess their significance to the climate. This is feasible using data from space-borne lidars such as CALIPSO, which fly in formation with other satellites like MODIS AQUA and MISR, as part of the A-Train constellation.
Highlights
The radiative impact of aerosols still remains one of the largest sources of uncertainty in predicting future climate conditions (IPCC, 2001)
Our study implies that a detailed statistical evaluation of the temporal frequency and spatial extent of elevated aerosol layers is necessary to assess their significance to the climate
We report airborne LIDAR measurements of aerosol extinction profiles measured over the east coast of India
Summary
The radiative impact of aerosols still remains one of the largest sources of uncertainty in predicting future climate conditions (IPCC, 2001). There exist a few recent studies on the vertical distribution of aerosols using aircraft based measurements over south central India (Moorthy et al, 2004; Gadhavi and Jayaraman, 2006). During the Indian Ocean Experiment (INDOEX) there were a few aircraft measurements of aerosols and measurements of aerosol altitude distribution using island-based and ship-borne lidars (Muller et al, 2001a, b; Welton et al, 2002; Pelon et al, 2002). The three-dimensional structure and the optical properties of the Indian pollution plume were investigated from airborne LIDAR and radiometric measurements over the Indian Ocean on three consecutive days (7, 8, and 9 March 1999) of the INDOEX’99 intensive field phase (Pelon et al, 2002). The measurements were carried out as part of the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB) field campaign
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