Studying the zonal slope of thermocline uisng Argo and altimeter observations

MM Ali, Uday Bhaskar, Ravichandran
Head, Oceanography Division
National Remote Sensing Agency
Balanagar
Hyderabad (India) 500037

After the onset of the Indian southwest monsoon, a jet of water flows from west to east along the equatorial Indian ocean (EIO) resulting in pilling up of water at the eastern end of the basin and changing the slope of the thermocline. Though slopes in SSHAs could be obtained from the accurate altimeter measurements,   the associated changes in the thermocline could not be studied in detail due to the lack of dense in situ temperature measurements, particularly, in the  EIO region. Deployment of Argo floats in the Indian Ocean gave an opportunity to study the seasonal changes in the thermocline in conjunction with altimeter observations.

Temperature profiles from Argo floats and the SSHAs from Jason during 2004 have been used to develop the relationship between the slopes in SSHA and the thermocline changes.    A west to east upslope in SSHA is observed during May-July and again during November-December 2004, showing bimodal oscillations. The corresponding slopes in the thermocline are in the opposite direction.  Up slopes (down slopes) in SSH and down slopes (up slopes) in  thermocline are maximum during June (September) 2004.   Variations in ! SSH and thermocline are large at the eastern end of the basin compared with the western end due to the pilling up of water at the eastern end and the associated changes in the thermocline. Using the relation between the two slopes, altimeter observations have been used to study the inter-annual and seasonal changes in the thermocline in relation to the monsoon pehnomenon.