HR: 12:08h
AN: A32B-08    [Abstracts]
TI: Modeling Optical Properties of Mineral Dust over "The Great Indian Desert"
AU: mishra, s
EM: mishrask@iitk.ac.in
AF: Indian Institute of Technology Kanpur INDIA, Department of Civil Engineering, Kanpur, 208016, India
AU: * TRIPATHI, S N
EM: snt@iitk.ac.in
AF: Indian Institute of Technology Kanpur INDIA, Department of Civil Engineering, Kanpur, 208016, India
AB: The Thar desert, sometimes also described as ‘The Great Indian Desert', lying in the Northwest part of India with an area of 0.32*106 km2, is known to be the source of natural mineral dust . The mineral dust particles are mostly non-spherical having sharp edges, which show different scattering signature compared to that of equivalent spheres while interacting with the radiation. Furthermore accurate mineralogical information, that governs their refractive indices, is essential for scattering calculations. The radiative impacts of dust particles therefore depend on their morphology and mineralogy. Most of the present satellites consider the particle to be spherical while retrieving their optical properties. Some newly launched spacecraft instruments such as MISR accounts for non spherical nature by including spheroid particles in its retrieval algorithm . Clearly there exits a need for improvement in dust model used in retrieval algorithm to account for their sharp edges together with their index of refraction based on the latest chemical composition at the sensing wavelengths. To the best of our knowledge no such attempt has been made to calculate the optical properties of dust particles over the Thar desert. In this study, the optical properties of mineral dust of the Thar desert has been modeled using T-matrix method with realistic dust shapes based on Scanning Electron Microscope images of the dust over the desert with particle size ranging from 0.1-1.0 ìm at wavelengths spanning from ultraviolet to near infrared (0.38-1.2ìm). Representative dust particles shapes considered are sphere, cylinder, spheroids and chebyshev together with realistic mineral dust composition. Mineralogical analysis of airborne dust over Northwest India has revealed the presence of only basic non-metallic minerals such as Quartz, Feldspar, Mica and Calcite, which posses negligible imaginary part of refractive index at considered wavelength domain, however, the subsequent dust sampling over Rajasthan desert has disclosed significant iron content , which causes sufficient absorption of solar radiation in the considered wavelength domain. This iron occurs in the form of Hematite (Fe2O3) as metallic mineral with varying contribution in the desert dust. The effective refractive index of composite mineral dust accounting for hematite (Fe2O3) has been calculated using Bruggman's effective medium mixing rule. Since no exact volume percentage of Hematite in Thar dust particles is known till date therefore optical properties of mineral dust over the Thar desert have been modeled by varying the metallic mineral. The results pertaining to optical properties such as scattering and absorption cross-sections, phase functions together with asymmetry parameter will be discussed.
UR: http://home.iitk.ac.in/~snt
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 1029 Composition of aerosols and dust particles
DE: 4801 Aerosols (0305, 4906)
DE: 4906 Aerosols (0305, 4801)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting