Abstract
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 quasigeostrophic 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 well overall with the observed MJO in scale and phase velocity within the factors.
Highlights
The Madden–Julian oscillation (MJO) is an atmospheric enigma [Hartmann and Hendon 2007; see Zhang (2005) for a review]
Explain the MJO in terms the dry dynamics? Under the linear limit, the large-scale tropical atmospheric dynamics consists of a set of the equatorial waves (Matsuno 1966; Yano and Bonazzola 2009)
The results are summarized in the phase space of cp and f0 in terms of the total duration of a stable propagation of the initial modon solution by Fig. 3: the modon solution is most stable for the range of the propagation speeds of 8–18 m s21
Summary
The Madden–Julian oscillation (MJO) is an atmospheric enigma [Hartmann and Hendon 2007; see Zhang (2005) for a review]. Theoretical efforts to explain the MJO in terms of an interaction between the large-scale atmospheric flow and moist convection are numerous to provide an exhaustive list but they include Hayashi (1970), Lindzen (1974), Emanuel (1987), Yano and Emanuel (1991), Fuchs and Raymond (2007), Raymond and Fuchs (2007, 2009), Majda and Stechmann (2009), Yang and Ingersoll (2011, 2013), and Adames and Kim (2016) These theories usually treat the MJO as a linear wave.
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