Intraseasonal oscillations of the Andaman Sea thermocline

Abstract

Variations in the upper ocean thermal structure have significant implications for air-sea interaction and upper-ocean ecosystem processes. Vertical profiles of temperature measured by a moored buoy located at 10.5°N, 94°E in the Andaman Sea and simulation by an Indian Ocean model are used in this study to characterise the intraseasonal variations (ISV) in the Andaman Sea (AndS) thermal structure and identify their sources. The seasonal variations in the upper ocean thermal structure show a strong semi-annual cycle driven by monsoons. The sub-surface temperature shows significant intraseasonal oscillations within a band of 40–110 days, which are de-coupled from that in the mixed layer, which has dominant periodicity in the band of 90–120 days. Thermocline ISV are seasonally modulated with a primary peak during August–September and a secondary peak during February–March, with significant year-to-year variations. A cross-wavelet analysis shows that ISV in the 40–60 days period is in phase with that at the eastern boundary and they are locally forced by the passage of eddies. The 60–110 day band is out of phase with the eastern boundary and is forced by Rossby waves radiated from the equatorially generated intraseasonal coastal Kelvin waves.