IN-SITU MEASUREMENTS OF AEROSOL EXTINCTION PROFILES AND THEIR SPECTRAL DEPENDENCIES AT TROPOSPHERIC LEVELS

Aerosol extinction coefficients are measured using rocket and balloon- borne photometers from Thumba (8.5-degrees-N) and Hyderabad (17.5-degr ees-N) respectively, in southern India. The spectral bands are selecte d within the 300 to 900 nm wavelength region. The aerosol extinction c oefficients are found to exhibit large temporal and spatial variations . The spectral dependence of aerosol extinction, derived using a simpl e Angstrom power law shows that the wavelength exponent parameter alph a is altitude dependent. The data are grouped into 2 categories, to st udy the seasonal variations, in aerosol parameters before and after th e Indian monsoon. In general, the premonsoon tropospheric aerosol exti nction coefficients are found to be higher compared to the postmonsoon values. Furthermore, a layer characterized by a low alpha value, situ ated around 13 km in most of the premonsoon data, is found to come dow n to about 11 km after the monsoon with a corresponding increase in al pha.