Mechanisms of variability and predictability of the tropical coupled ocean-atmosphere system |
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Authors: | B N Goswami Sudha Selvarajan V Krishnamurthy |
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Institution: | (1) Centre for Atmospheric Sciences, Indian Institute of Science, 560012 Bangalore, India;(2) International Institute for Earth, Environmental and Marine Sciences and Technologies, 34014 Miramare, Trieste, Italy |
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Abstract: | A conceptual model is proposed to explain the observed aperiodicity in the short term climate fluctuations of the tropical
coupled ocean-atmosphere system. This is based on the evidence presented here that the tropical coupled ocean-atmosphere system
sustains a low frequency inter-annual mode and a host of higher frequency intra-seasonal unstable modes. At long wavelengths,
the low frequency mode is dominant while at short wavelengths, the high frequency modes are dominant resulting in the co-existence
of a long wave low frequency mode with some short wave intra-seasonal modes in the tropical coupled system. It is argued that
due to its long wavelength, the low frequency mode would behave like a linear oscillator while the higher frequency short
wave modes would be nonlinear. The conceptual model envisages that an interaction between the low frequency linear oscillator
and the high frequency nonlinear oscillations results in the observed aperiodicity of the tropical coupled system. This is
illustrated by representing the higher frequency intra-seasonal oscillations by a nonlinear low order model which is then
coupled to a linear oscillator with a periodicity of four years. The physical mechanism resulting in the aperiodicity in the
low frequency oscillations and implications of these results on the predictability of the coupled system are discussed. |
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Keywords: | Aperiodicity inter-annual variability tropical coupled ocean-atmosphere system predictability convergence feedback multiple periodic attractors low frequency oscillator non linear intra-seasonal modes |
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