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Ocean-Atmosphere coupling on different spatio-temporal scales

Ocean-Atmosphere coupling on different spatio-temporal scales. Lei Zhou Raghu Murtugudde. 16th Conference on Air-Sea Interaction, Phoenix, AZ Jan. 15, 2009. Introduction. Evidence for OA interaction: ENSO. NOAA / PMEL / TAO. Introduction. Evidence for OA interaction: MJO.

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Ocean-Atmosphere coupling on different spatio-temporal scales

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  1. Ocean-Atmosphere coupling on different spatio-temporal scales Lei Zhou Raghu Murtugudde 16th Conference on Air-Sea Interaction, Phoenix, AZ Jan. 15, 2009

  2. Introduction • Evidence for OA interaction: ENSO NOAA / PMEL / TAO

  3. Introduction • Evidence for OA interaction: MJO Image courtesy of Science/AAAS

  4. Introduction • Implicit assumption a priori: The spatial and temporal scales in the ocean and the atmosphere should be similar. • Some inconsistent evidence: • MJO-induced Kelvin waves have a period of ~70 days, which is longer than that of MJOs • Intraseasonal SSTAs in the Indian Ocean are ~ hundreds km, while MJOs are ~ thousands km.

  5. Introduction • So, any other possibilities? • Assumption: • The ocean and the atmosphere can interact with each other on different spatial and temporal scales. • Scale similarity is not necessary for the ocean-atmosphere coupling.

  6. Review of uncoupled system • Conclusion first: • No unstable waves in the linear uncoupled system; • Thus, the unstable waves shown below in the coupled system are only attributable to the air-sea interactions.

  7. Review of uncoupled system The ocean: For the barotropic, tropical ocean, the linear inviscid governing equations with no atmospheric forcing are adopted from Gill (1982)

  8. Review of uncoupled system The atmosphere: For the barotropic atmosphere in the tropics, the governing equations without oceanic feedbacks are applied following Anderson and McCreary (1985),

  9. Coupled System The ocean The atmosphere

  10. With the same processes as above, we obtain Assumptions used to obtain the above equations: Meridional winds V are neglected Linear approximation The following results are not sensitive to the parameters.

  11. Two Possibilities • In order to solve the coupled equations, we need to assume wavelike solutions • If the spatial and temporal scales are the same in the ocean and the atmosphere • If the spatial and temporal scale are NOT the same in the ocean and the atmosphere

  12. Scales are the same … The wavelike solutions of the form and are assumed.

  13. From the real part, the following condition must be satisfied

  14. Scales are different … Representing the wave properties in the ocean with a subscript o, and the wave properties in the atmosphere with a subscript a, Eq. (5) is re-written as

  15. In order to have non-trivial solutions, the following condition has to be satisfied

  16. Inverse of the imaginary part of the unstable solution, with the unit of day

  17. Substituting into we have

  18. Inverse of the imaginary part of one solution, with the unit of day

  19. Conclusion The oscillations with different temporal and spatial scales can interact with each other and lead to instabilities in both the ocean and the atmosphere in a linear framework.

  20. Thanks !

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