Abstract:
Optical and micro-physical features of aerosol
are reported using Skyradiometer (POM-01L, Prede, Japan)
observations taken from a high-altitude station Merak,
located in north-eastern Ladakh of the western transHimalayas region during January 2011 to December 2013.
The observed daily mean aerosol optical depth (AOD, at
500 nm) at the site varied from 0.01 to 0.14. However,
75 % of the observed AOD lies below 0.05 during the
study period. Seasonal peaks of AOD occurred in spring
as 0.06 and minimum in winter as 0.03 which represents
the aged background aerosols at the site. Yearly mean AOD
at 500 nm is found to be around 0.04 and inter-annual
variations of AOD is very small (nearly ±0.01). Angstrom
exponent (α) varied seasonally from 0.73 in spring to 1.5 in
autumn. About 30 % of the observed α lies below 0.8 whichare the indicative for the presence of coarse-mode aerosols
at the site. The station exhibits absorbing aerosol features
which prominently occurred during spring and that may be
attributed by the transported anthropogenic aerosol from
Indo-Gangatic Plain (IGP). Results were well substantiated
with the air mass back-trajectory analysis. Furthermore, seasonal mean of single scattering albedo (SSA at 500 nm)
varied from of 0.94 to 0.98 and a general increasing trend
is noticed from 400 to 870 nm wavelengths. These features
are apparently regional characteristics of the site. Aerosol
asymmetry factor (AS) decreases gradually from 400 to
870 nm and varied from 0.66 to 0.69 at 500 nm across the
seasons. Dominance of desert-dust aerosols, associated by
coarse mode, is indicated by tri-modal features of aerosol
volume size distribution over the station during the entire
seasons.
