The interaction between the Western Indian Ocean and ENSO in CESM

Abstract

Several previous studies have suggested that a cool western Indian Ocean may induce convection over Indonesia, leading to surface convergence and easterlies over the western equatorial Pacific Ocean. These easterlies then increase the Pacific Warm Water Volume favouring El Niño in the next year. We investigate this mechanism of Indian-Pacific interaction using output from two simulations (at 0. 1 ∘ and 1 ∘ ocean model resolution) with the Community Earth System Model (CESM). No conclusive evidence for the suggested interaction mechanism is found in CESM. Like many other coupled models, CESM has an overly strong sea surface temperature variability in the eastern Indian Ocean due to an exaggerated sensitivity of the sea surface temperature to thermocline variations. Due to this bias the effect of the western Indian Ocean signals on the Pacific, as found from observational analysis, is hidden. Our analysis shows that this bias can be traced to errors in the time-mean vertical temperature profile in the Indian Ocean. This bias needs to be reduced to allow a better investigation of the subtle interactions between the Indian and Pacific Oceans.