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MISU IMI Seminar | Jun-Ichi Yano

Tropical Atmospheric Madden-Julian Oscillation: Strongly-Nonlinear Free Solitary Rossby Wave?

by Jun-Ichi Yano, French National Centre for Scientific Research, Paris, France

Time: 22 May 2018, 11h15–12.15
Venue: Rossbysalen C609, Arrhenius Laboratory, 6th floor

Jun-Ichi Yano, French National Centre for Scientific Research, Paris, France

Abstract
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 if it is to be understood by dry dynamics, the MJO is most likely a strongly nonlinear solitary Rossby wave. Under a global quasi-geostrophic equivalent-barotropic formulation, 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 greatest longevities compare overall well with the observed MJO in scale and phase velocity within the factors.

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