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Monday 25 Sep 2017Tropical atmospheric Madden-Julian oscillation: strongly-nonlinear free solitary Rossby wave?

Dr. Jun-Ichi Yano - CNRM, Meteo France, Toulouse

H103 14:30-15:30

The Madden-Julian oscillation (MJO), a planetary-scale eastward propagating coherent structure with periods of 30-60 days, is a prominent manifestation of intraseasonal variability in the tropical atmosphere. It is widely presumed that small-scale moist cumulus convection is a critical part of its dynamics. However, the recent results from high-resolution modeling as well as data analysis suggest that the MJO may be understood by dry dynamics to a leading-order approximation. Simple, further theoretical considerations presented herein suggest that the MJO is most likely a strongly nonlinear solitary Rossby wave, if it is to be understood by dry dynamics. Under a global quasi-geostrophic equivalent-barotropic formulation, the modon theory provides such analytic solutions. Stability and the longevity of the modon solutions are investigated with a global shallow water model. The preferred modon solutions with the highest longevities compare overall well with the observed MJO in scale and phase velocity within the factors.

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