Seasonal and Interannual Sea Surface Temperature Variability in the Coastal Cities of Arabian Sea and Bay of Bengal

摘要

The sea surface temperature (SST) variations play a very important role in the genesis and maintenance of meteorological and oceanographic processes such as monsoon depressions and subsequent floods, large-scale sea level fluctuations and genesis of t ropical cyclones. Many low lying coastal regions of South Asia are adjacent to river deltas and have large population. The dense population, poor economy and several other socio-economic factors make these areas most vulnerable to the impact of climate c hange. Variability of sea surface temperature (SST) is important as the duration and intensity of SST provide the basis for studies related to climatic change scenario. In this study an attempt has been made to estimate the recent SST trends in the coast al waters of some cities, which lie on the Arabian Sea and Bay of Bengal. The annual and interannual variability has also been studied. The SST variations have then been linked with the El Nino and La Nina events. The NOAA-NASA Pathfinder Advanced Very H igh Resolution Radiometer (AVHRR) SST fields from 1985-1998, created in the Jet Propulsion Laboratory (JPL), USA are used in this study. Here the quality of data is an important factor to obtain reliable estimates of Sea Surface Temperature (SST) trends and other related parameters. However, this is not possible with the conventional type data, due to low quality as well as sparse data in the region. Though the satellite based SST climatologies have shorter observation lengths, they can provide reliable estimates of recent SST variability over a large oceanic areas with sparse or no data. Increasing trend of SST is observed throughout all the seasons in the northern Arabian Sea extending from Oman to Karachi and Mumbai and further south to Salalah and Colombo. However, in coastal islands stations further south of India such as at Colombo the increment is not significant. Though the increasing trend in SST during winter is not significant, nevertheless it shows the increasing influence of cold spells o n this Island. An interesting situation has been observed in the Bay of Bengal. On an average, increasing trends in the annual SST were observed in Visakhaputnam. But at the stations located in the northeastern part of Bay of Bengal, namely Hiron Point a nd Cox's Bazar reverse conditions are observed. In the Southern Bay of Bengal variations in SST is not significant which reflects in the SST analysis of Chennai and Port Blair stations. Location of these stations at lower latitudes (near by equator) prob ably is the reason for this insignificant change. It has been found that the interannual mode of SST variations dominate the linear SST trends which is characterized by the El Nino Southern Oscillations (ENSO) scale cycle.