Abstract
The present study analyzes simultaneous and collocated measurements of spectral columnar aerosol optical depth (AOD) and the variations in total mass concentration of near surface aerosols in the marine atmosphere over the Bay of Bengal (BoB) during the winter phase of the Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) expedition of December and January 2008/2009 on board the Oceanographic Research Vessel (ORV) of Sagar Kanya. High AOD500 values (＞ 0.8) are found close to coastal regions in the western and northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plain (IGP). In these regions, the Angstrom exponent α380–1020 values are also found to be high (~1.2–1.3), indicating relative abundance of accumulation-mode continental aerosols. Low AOD500 (0.1–0.2) values are observed in central and southern BoB, far away from the mainland. The AOD500 and total aerosol mass loading increased along with the latitude. The total mass concentration is found to vary between 15 μg/m3 and 45 μg/m3, with higher loadings near the east coast and northern parts of the BoB. NCEP reanalysis of the data with winds at 925 hPa, along with airmass trajectories calculated using the HYSPLIT model, suggest transport of continental aerosols from central and northern India over the BoB at lower heights, and mineral dust aerosol transport from arid regions in the west of India at higher altitudes; while the increase in aerosol loading over eastern BoB was strongly affected by airmasses originating from Southeast Asia. The spatial correlation map between the MODIS and MISR AOD data is analyzed, revealing a strong correlation between the two datasets. The influence of wind speed and continental airmass on AOD is also examined, which provides information on the effects of the adjoining landmass on the marine aerosol field.
Highlights
The role of tropospheric aerosols in the radiation budget of the atmosphere is one of the least understood but crucial aspects of the global climate system (Haywood and Boucher, 2000)
The variations in daily aerosol optical depth (AOD) observed large fluctuations at shorter wavelengths (~3 times higher than those measured at the longer ones) for all the days of the W-ICARB campaign in the Bay of Bengal (BoB) region which is shown in Fig. 5 indicating the dominance of smaller size aerosols
The mean AOD500 during W-ICARB was found to be 0.35 ± 0.07 which is comparable in magnitude with the (0.36 ± 0.12) found over BoB during ICARB 2006 (Kalapureddy and Devara, 2008)
Summary
The role of tropospheric aerosols in the radiation budget of the atmosphere is one of the least understood but crucial aspects of the global climate system (Haywood and Boucher, 2000). The variations in daily AOD observed large fluctuations at shorter wavelengths (~3 times higher than those measured at the longer ones) for all the days of the W-ICARB campaign in the BoB region which is shown in Fig. 5 indicating the dominance of smaller size aerosols.
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