Effect of the 2004 ‘Boxing Day’ Tsunami on Water Properties and Currents in the Bay of Bengal

Problem statement: Variation of temperature, salinity and geostrophic current in the Bay of Bengal due to the 2004 Boxing Day tsunami was investigated in this project using ARGO float and absolute dynamic height topography data. This was done to determine the effect of the tsunami on the water properties in the bay. Approach: The study area was between latitudes 5º N and 25º N and longitudes 75º E and 100º E. Data from November 2004 and January 2005 were analyzed. The drift velocity of the ARGO float (within the study area) at its parking depth was calculated and compared with the geostrophic current at this depth in order to determine the appropriate reference level (level of no motion) for the study area. Results: The geostrophic current, using the Helland-Hansen equation, requires a reference level, which was then used to calculate the surface geostrophic current using the absolute dynamic height obtained from satellite altimetry. The appropriate level of no motion in the Bay of Bengal region was found to be 1500 m. As a result of the tsunami, the variation in sea surface temperature was around 2- 3ºC and the variation in salinity was around 2-3 psu in the region. Accordingly, the dynamic height increased to about 20-30 dym cm just after the tsunami and abruptly changed the geostrophic surface currents pattern in Bay of Bengal. A few days after the tsunami, the geostrophic surface currents returned to normal. Conclusions: The variation of temperature and salinity in the Bay are the major causes of changes in the dynamic height, which results in the variation of geostrophic currents