Environmental studies of the Arabian Sea using remote sensing, GIS and GPS techniques
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The Arabian Sea, situated in the western part of the northern Indian Ocean is a tropical basin. It is bounded on the east by the Indian peninsula, on the north by Baluchistan and Sindh provinces of Pakistan and on the west by the landmass of Arabia and Africa. The environmental factors that influence this tropical basin are the seasonally changing winds from the northeast during winter (November-February) and southwest during summer (June to September). Accordingly, the waters of the basin will experience seasonal variations. The present study aims at understanding the seasonal and inter-annual variation of the Arabian Sea using satellite derived data with the help of GIS technique. The spatial domain selected for the present study is 40oE and 78oE longitude and equator to 30o N. The remote sensing data with respect to sea surface temperature (SST), sea surface wind, sea surface height (SSH), and chlorophyll pigment concentration during January 2002 to December 2005 were used to understand the spatio-temporal variability of the Arabian Sea. The monthly mean SST data was obtained from Modis aqua, winds from Quikscat and chlorophyll pigment concentration from SeaWiFS. The SSH anomaly data was obtained from the merged product - Topex/Poseidon ERS ½ satellite which is 7-day snapshot. The spatial resolution of these data is 0.3o latitude x 0.3o longitude. Geographical information system (GIS) was used for processing and analyzing the above parameters to determine the variability and detection of oceanic processes that are responsible for such variability. The study showed a very strong inverse relation between SST and chlorophyll concentrations. Arabian Sea undergoes seasonal cooling during summer due to upwelling and advection, and in winter due to surface cooling under reduced solar heating. Upwelling along the coasts of Somalia, Arabia, and the west coast of India brings cold and nutrient rich sub-surface waters to the surface, which supports the observed high chlorophyll concentrations. During winter the convective mixing in the northern Arabian Sea supports high chlorophyll pigment concentrations. Due to strong solar heating, SST was warmest in spring (April), which supported least chlorophyll concentration. The SST, chlorophyll pigment concentrations and sea surface height showed large inter-annual variability during the study period 2002 to 2005 during both winter (January) and summer (August). Of the four years analyzed, the winter was coldest in 2002 and warmest in 2003. In summer, the coldest temperature along the western boundary occurred in 2004 while the warmest was in 2002. However, the occurrence of chlorophyll pigment concentrations did not exactly follow the variations in SST pattern. The occurrence of negative SSH anomaly along the eastern and western boundary showed some variation from one year to the other. The extent to which the negative SSH moved westward is an indication of Rossby wave propagation, which also showed some inter-annual variability.
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