Study of total column atmospheric aerosol optical depth,ozone and precipitable water content over Bay of Bengal during BOBMEX-99 |
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Authors: | K K Dani R S Maheskumar P C S Devara |
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Institution: | (1) Physical Meteorology and Aerology Division, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Marg, 411 008 Pune, India |
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Abstract: | The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation
of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the
columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out
using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th
August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths
covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band
around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99
have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment.
The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance
of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the
present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due
to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal
variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease
during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed
maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater
as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high,
there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols
over the study region. |
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Keywords: | Bay of Bengal total column aerosol optical depth size distribution ozone precipitable water content ship TOMS satellite |
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