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Abstract:
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The objective of this study is to understand the reasons for the enhancement in
aerosol optical depth (AOD) over the Arabian Sea observed during June, July and
August. During these months, high values of AOD are found over the sea beyond
10◦ N and adjacent regions. The Arabian Sea is bounded by the lands of Asia
and Africa on its three sides. So the region is influenced by transported aerosols
from the surroundings as well as aerosols of local origin (marine aerosols). During
the summer monsoon season in India, strong surface winds with velocities around
15 m s−1 are experienced over most parts of the Arabian Sea. These winds are capable
of increasing sea spray activity, thereby enhancing the production of marine
aerosols. The strong winds increase the contribution of marine aerosols over the
region to about 60% of the total aerosol content. The main components of marine
aerosols include sea salt and sulphate particles. The remaining part of the aerosol
particles comes from the western and northern land masses around the sea, of
which the main component is transported dust particles. This transport is observed
at higher altitudes starting from 600 m. At low levels, the transport occurs mainly
from the Indian Ocean and the Arabian Sea itself, indicating the predominance
of marine aerosols at these levels. The major portion of the total aerosol loading
was contributed by coarse-mode particles during the period of study. But in the
winter season, the concentration of coarse-mode aerosols is found to be less. From
the analysis, it is concluded that the increase in marine aerosols and dust particles
transported from nearby deserts results in an increase in aerosol content over the
Arabian Sea during June, July and August. |