Effect of surface wind and wind vectors on sea surface chlorophyll a distribution in the ocean waters surrounding Sri Lanka for the period 1999 - 2003

Abstract

Ocean colour and surface wind data derived from Sea viewing Wide Field of view Sensor (SeaWiFS) were examined to understand the relationship between a biological parameter, chlorophyll a and a physical parameter, surface wind. SeaWiFS data of 1.1 km resolution for the period 1999-2003 were processed and mapped to produce daily maps of chlorophyll a, wind speed, meridional wind (mwind) and zonal wind (zwind) speeds within the area of latitudes between 2.0N - 13.5N and longitudes between 76.5E - 88.0E. Monthly composites for the period 1999-2003 were produced. The chlorophyll concentration variability showed a very strong relation to the monsoonal pattern in the Indian Ocean region. A strong co-variability was found between the wind parallel to the coast, and the chlorophyll concentration in South and Southwest regions during the southwest monsoon period and in Northeast and East regions during the northeast monsoon period, respectively, and the corresponding correlation coefficients were found to be between 0.92 - 0.99 in the four regions. It was observed that mwind is the major contributor to the wind parallel to the coast, in the Northeast and East regions with correlation coefficients in the range 0.82 - 0.88 during northeast monsoon period. Whereas zwind contributes to the wind parallel to the coast, in the South and Southwest regions exhibiting correlation coefficients in the range 0.97 - 0.99 during southwest monsoon period. High chlorophyll a concentrations observed in these waters can be a result of coastal upwelling.