Determination of dynamic heights in the Bay of Bengal from XBT profiles and climatological salinities

Abstract

Dynamic height (DH) computations are necessary for the estimation of geostrophic currents, heat transport studies, identification of eddies and to validate the altimeter sea surface height (SSH) observations. To compute DHs we need the temperature and salinity profiles to a reasonable deeper level. But, temperature profiles alone, such as from XBT (expendable bathy thermograph), are more numerous than combined temperature and salinity measurements from CTD (conductivity, temperature and depth). To use these voluminous temperature measurements from XBT observations in the computation of DHs, temperature/salinity relations were developed in many oceanic regions. Since such an exercise cannot be carried out in the Bay of Bengal due to the absence of adequate CTD measurements, we have proposed a method of utilizing XBT measurements and climatological (Levitus and Boyer, 1994) salinities to compute the DHs. The approach is demonstrated by replacing the CTD salinities with the climatological salinities. The relative errors compared to the DH signals are 3.8%, 2.7% and 2.6% for 200, 700 and 1000 dbar levels, respectively. The DHs relative to 700 dbar computed using the XBT temperature and climatological salinity profiles are compared with the SSH observations from TOPEX altimeter. The standard deviation of the difference between the DHs computed after converting to geometrical units and SSH is 7.3 cm.