• Sandhya K Nair

      Articles written in Journal of Earth System Science

    • Impact of aerosols from the Asian Continent on the adjoining oceanic environments

      K Parameswaran Sandhya K Nair K Rajeev

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      Aerosol optical depth (AOD) at 630nm wavelength over the oceanic regions adjoining the Asian Continent is examined using a seven-year long data base derived from the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA satellite to study the mean spatial and temporal variations as well as to understand the impact of aerosols advecting from the continent. Depending on the prevailing meteorological conditions and nature of synoptic circulation, the AOD over the oceanic region shows a systematic annual variation. This annual pattern inturn also shows an inter-annual variability because of the corresponding variations in the meteorological features over the continent as well as small-scale deviations in the nature of synoptic circulation. The annual variation over the oceanic regions also shows a pronounced spatial heterogeneity depending on the influence of continental aerosols. Making use of the wind speed dependence of sea-salt AOD at far-oceanic environments and monthly mean wind speeds at small grids of size 5° × 5°, the annual variation of sea-salt AOD at different locations is studied to understand the spatial heterogeneity of this component. The residual component obtained by subtracting this from the measured AOD is the non-oceanic component due to advection from continent. The source regions for major continental advections are delineated from the analysis of air-mass back trajectories at appropriate locations identified from the annual pattern of non-oceanic component. The long-term effect of the continental impact is examined from the mean trend of AOD over the three major oceanic regions. This study shows that the continental influence is most significant over the Arabian Sea, followed by the Bay of Bengal and is almost insignificant in most of the regions over the Southern Hemispheric Indian Ocean, except for the effect of smoke aerosols over a few locations near Indonesia and Madagascar.

    • Impact of continental meteorology and atmospheric circulation in the modulation of Aerosol Optical Depth over the Arabian Sea

      Sandhya K Nair S Sijikumar S S Prijith

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      Time series analysis of Aerosol Optical Depth (AOD) derived from NOAA-AVHRR data during the period 1996–1999 and the MODIS data during 2000–2009 over the Arabian Sea revealed a systematic biennial variability in the high AOD during summer months. The variability is more prominent over the northern and central parts of the Arabian Sea and became less significant towards southern latitudes. The possible mechanisms for these are examined by estimating the source strength over coastal Arabia and AOD flow rate through the western boundary of the Arabian Sea. Both these show clear signatures of biennial variability with same phase as AOD for most of the years. This result indicates that the observed biennial variability in AOD is likely to be the outcome of combined effects of biennial variability in wind generated sea-salt aerosols and dust transported from Arabia.

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