Analysis of freshwater flux climatology over the Indian Ocean using the HOAPS data

Abstract

Estimation of freshwater flux over a certain region is very difficult, as it needs both accurate evaporation and precipitation rates over the study area. Over the Indian Ocean (IO), the precipitation estimates are totally lacking or unknown due to the lack of in-situ measurements. In the present study, we examine the climatology and the annual cycle of the freshwater flux over the IO using the newly available Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data (HOAPS). This data set has been derived from passive microwave and infrared satellite data utilising the data from the Special Sensor Microwave/Imager (SSM/I) and the Advanced Very High Resolution Radiometer (AVHRR). We have compared the freshwater flux estimates from HOAPS data set with the earlier estimates to see how they differ from the older estimates. The evaporation rates from HOAPS are significantly different from the earlier estimates. The annual cycle of freshwater flux shows that the Bay of Bengal (BB) is a moisture convergence region most of the year as compared to the Arabian Sea (AS), which is a moisture flux divergence region. Further, the build-up of moisture in the southern Indian Ocean (SIO) is also clearly seen from March to June, indicating its major role in the summer monsoon activity over the Indian subcontinent. An analysis of monthly mean freshwater flux indicates that a small part of the southwest coast of India and southern parts of the BB region receives freshwater in April almost 2 months ahead of the onset of the summer monsoon.