Atmospheric aerosol studies under ISRO's Geosphere Biosphere Programme

Abstract

The importance of aerosols in the radiation budget and energetics of the atmosphere has been known for a long time now. In recent years there has been a growing recognition of the potential of aerosols for producing short term and long term changes in climate not only due to major volcanic eruptions such as EI Chichon nad Mr. Pinatubo but also due to the impact of increasing anthropogenic activities such as fossil fuel burning, land use changes and industrial activities e.g. ecment manufacturing. Further, aerosols have now been found to play a vital role in the ozone depletion phenomenon specifically in the development of the Antartic Ozone Hole. These developments have made a systematic monitoring of atmospheric aerosols one of the major areas of Atmospheric Science Research. Attempts are being made to incorporate aerosols in climate perturbations. Aerosol characteristics exhibit spatial as well as temporal variations and there are regional features which need to be delineated from global features in these model studies. Aerosol data is meager when compared to other atmospheric parameters for any part of the globe. This is more serious in the tropics specifically in the Indian region. Under ISRO's Geosphere Biosphere Programme several projects have been taken up to overcome this lacuna. A network of Multi wavelength Radiometer MWR stations has been set up at different locations to cover different types of environment eg. rural, urban, coastal, marine etc. Spectral aerosol optical depths and columnar size distribution are being regularly monitored at Trivandrum, Mysore, Visakhapatnam, Pune and more recently at the island station Minicoy and the arid desert site Jodhpur. Several of these stations have collected data for about ten years now. Additional MWR units are being set up at Anantapur and Dibrugarh. Ballon experiments have been conducted from Hyderabad to obtain the vertical distribution of the optical parameters of aerosols hat are required for radiation budget calculations under both volcanically perturbed as well as quiescent conditions. Aerosol characteristics can also be estimated from satellite remote sensed data. A programme has been initiated to estimate aerosol optical depths over ocean surfaces from AVHRR data and more recently the Indian Remote Sensing Satellite IRS-P3 MOS data. The wavelength region covered by the Ocean Color Monitor sensor on the recently launched IRS-P4 satellite OCEANSAT provide very good opportunity for retrival of aerosol data. This paper presents a brief review of the scientific results obtained from these programmes so far.