| dc.description.abstract | This thesis focusses on investigating the aerosol characteristics over Asian region using satellite remote sensing. Seven years of aerosol optical thickness (AOT) product from MODerate Imaging Spectroradiometer (MODIS) onboard Aqua and Terra satellites during the years 2002-2008 are analyzed for the study. Ground observations of aerosol robotic network (AERONET) at different stations within the study area are used to validate the MODIS AOT. Angstrom exponent (AE), and fine mode fraction (FMF) from MODIS and AERONET are used to discuss the size, type and possible sources of the particles. National Center for Environmental Prediction, National Center for Atmospheric Research (NCEP-NCAR) reanalysis data and Global Precipitation Climatology Center (GPCC) data are used to obtain the meteorological parameters over the study area.
A detailed correlation analysis of AOT and AE has been carried out to validate the MODIS data using corresponding AERONET measurements over 16 selected stations. Behavior of the MODIS-AERONET correlation in different seasons is investigated to understand the response of the two measurements for varying aerosol types. The results indicate very high (> 0.9) correlation of AOT between MODIS and AERONET, while the corresponding AE correlation is poor, but seems to improve if only those data points with corresponding AOT > 0.5 are considered.
Further analysis is carried out to examine permanent aerosol source regions over Asia. The methodology involves taking average AOT map during the years over the region in different seasons, in which the permanent source regions will appear pronounced whereas the locations influenced by transport or any emissions that last shorter time period will be smoothened. The results reveal four main such source regions: (1) the region at North and North-West of China and South of Mongolia, (2) Eastern part of China, (3) North-East of Indian continent, and (4) Parts of Thailand, Vietnam and Indonesia. The average AOT trends over the source regions in the years are examined in different seasons together with the corresponding variations of meteorological parameters and the results suggest an increase in the emissions.
In order to understand how the permanent source regions influence the surrounding locations, the aerosol properties selected East Asian stations of Beijing, Gosan, Osaka, Taipei, Mukdahan, and Bac-Gaing are further investigated in detail. The daily, monthly, seasonal, and inter-annual variations of the AOT are described along with meteorological parameters from NCEP-NCAR reanalysis and GPCC data. AE and FMF from MODIS and AERONET are used to discuss the size, type of particles. Seasonal wind pattern are used to understand the transport of particles from the source regions to the chosen stations. The results suggest that maximum aerosol loading occur over Beijing with daily mean AOT reaching above 2.0. Gosan and Taipei are among the stations having smallest AOT in most of the seasons with values below 0.5. The detail analysis of the AOT characteristics over Mukdahan, and Bac-Giang are reported for the first time. Dust influence appears to be significant over Beijing, Osaka, as well as Gosan, and to a lesser extent over Bac-Giang in the spring, while pollution, bio-mass burning, etc. contribute in the summer and spring over all the stations. The increasing AOT trend over the permanent source region (1) mentioned above seems to result in the observed increase of AOT trend over Osaka and Gosan, and also over Beijing.
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