Spatial variations in aerosol characteristics and regional radiative forcing over India: Measurements and modeling of 2004 road campaign experiment

Results from a variety of complementary aerosol measurements made as part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP) road campaign experiment conducted during Feb 2004 in the central Indian region are reported. An instrumented vehicle fitted with the Micro Pulse Lidar for aerosol vertical profile measurements, nephelometer for scattering and athelometer for absorption coefficients measurements, Microtops II sun-photometer for column aerosol optical depth, Quartz Crystal Microbalance for aerosol mass concentration and Grimm spectrometer for aerosol number concentration was used in the campaign. The synergy of results from these complementary measurements is reflected in the computed aerosol radiative forcing for the region. We show that the large spatial and temporal variations found in the aerosol characteristics over the northwest Indian region are caused mainly by the naturally produced dust particles. The variation in their concentration modulates the overall atmospheric radiative forcing over this region. We also show that apart from the large north to south gradient in aerosol forcing caused due to transport of aerosols from the continent to the Indian Ocean region and reported during INDOEX, there is also a positive gradient in aerosol forcing from west to east, from the Arabian Sea to the Bay of Bengal region. A considerable portion of particles produced from the Indian main land is flushed to the Bay of Bengal region before being transported to the Indian Ocean, causing this west to east gradient.