4.12
A mechanism of the MJO based on interactions in the frequency domain
T.N. Krishnamurti, Florida State University, Tallahassee, FL; and D. R. Chakraborty, N. Cubukcu, L. Stefanova, and T. S. V. Vijaya Kumar
The surface and boundary layer fluxes of moisture exhibit a large amplification as the waves in the MJO time scales interact with synoptic time scales of 2 to 7 days. This amplification is clearly seen when the data sets are cast in the frequency domain for computations of the respective fluxes. Those flux relations carry triple product non-linearities, and the fluxes on the time scale of MJO are evaluated using co-spectra of triadal frequency interactions. The trigonometric selection rules on interactions among these frequencies are largely satisfied by the MJO time scales and two other time scales that reside in the synoptic time scales. Tropical instabilities provide a rich family of tropical disturbances that appear to be ready and waiting to interact with the MJO time scales (since these do satisfy the selection rules for non-vanishing interactions). A consequence of these non-linear interactions in the frequency domain is a two- to three-fold amplification of the surface fluxes. Although this analysis does not address how a small signal in the sea surface temperature on the time scale of the MJO arises in a coupled atmosphere-ocean model, we are able to show that its presence enables a large amplification of this time scale vertically across the planetary boundary layer. Given a low frequency ocean with many time scales, this process amplifies the fluxes on the time scale of MJO, this amplification eventually feeds back to the ocean via amplified surface stresses and an equilibrium state with a robust MJO in the coupled system is realized. The data sets for this study were derived from a coupled ocean-atmosphere model that was able to resolve a robust MJO in its simulations. This study also examines the character of sensible heat fluxes and momentum within the same framework.
Session 4, Climate Models: Evaluation and Projections, Part I (Room 608)
Tuesday, 13 January 2004, 8:30 AM-3:15 PM, Room 608
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