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Ann. Geophys., 26, 1365-1377, 2008
www.ann-geophys.net/26/1365/2008/
© European Geosciences Union 2008
Estimation of the effect of long-range transport on seasonal variation of aerosols over northeastern India
M. M. Gogoi1, P. K. Bhuyan2, and K. Krishna Moorthy1
1SPL, VSSC, Trivandrum 695 022 India
2Department of Physics, Dibrugarh University, Dibrugarh 786 004 India
Abstract. Spectral aerosol optical depth (AOD) at ten discrete channels in the visible
and near IR regions were estimated over Dibrugarh, located in the northeastern
part of India, using a ground-based multi-wavelength solar
radiometer (MWR) from October 2001 to February 2006. The observations reveal
seasonal variations with low values of AODs in retreating monsoon and high
values in the pre-monsoon season. Generally the AODs are high at shorter
wavelengths and low at longer wavelengths. AOD spectra are relatively steep
in winter compared to that in the monsoon period. The average value of AOD
lies between 0.44±0.07 and 0.56±0.07 at 500 nm during
the pre-monsoon season and between 0.19±0.02 and 0.22±0.02 during
re-treating monsoon at the same wavelength. Comparison of MWR observation on
Dibrugarh with satellite (MODIS) observation indicates a good correspondence
between ground-based and satellite derived AODs. The synoptic wind pattern
obtained from National Centre for Medium Range Weather Forecasting (NCMRWF),
India and back trajectory analysis using the NOAA Hybrid Single-Particle
Lagrangian Integrated Trajectory (HYSPLIT4) Model indicates that maximum
contribution to aerosol extinction could be due to transport of pollutants
from the industrialized and urban regions of India and large amounts of
desert and mineral aerosols from the west Asian and Indian desert. Equal
contributions from Bay-of-Bengal (BoB), in addition to that from the Indian
landmass and west Asian desert leads to a further increase of AOD over the
region of interest in the pre-monsoon seasons.
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