A skeleton model for the MJO with refined vertical structure

Thual, Sulian; Majda, Andrew J.

doi:10.1007/s00382-015-2731-x

Cited by 18 publications

(9 citation statements)

References 38 publications

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“…[], with the sole exception that the zonal average of the radiative cooling term,

\overset{s^{θ} ((), x)}{true}

, is set equal to 1.0 K d −1 and 1.33 K d −1 for the idealized warm pool and observed SST cases, respectively. Although the skeleton model has recently been amended to include a seasonally migrating warm pool and multiple meridional modes [ Thual et al ., ], in addition to a refined vertical structure [ Thual and Majda , ], we restrict our initial discussion to the stochastic and deterministic model simulations using the idealized and observed annual average SSTs.…”

Section: Resultsmentioning

confidence: 89%

Evaluating MJO event initiation and decay in the skeleton model using an RMM‐like index

et al. 2015

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The Madden‐Julian oscillation (MJO) skeleton model is a low‐order dynamic model that is capable of simulating many of the observed features of the MJO. This study develops a model‐based “MJO” index that is similar to the well‐known real‐time multivariate MJO (RMM) index to better facilitate comparison between the skeleton model and observational data. Multivariate and univariate empirical orthogonal function (EOF) analyses were performed on the convective heating and zonal wind data taken from the skeleton model for simulations forced with an idealized warm pool and observed sea surface temperatures (SSTs). The leading EOF modes indicated a wave number 1 convectively coupled circulation anomaly with zonal asymmetries that closely resembled the observed RMM EOFs, especially when the model was forced with observed SSTs. The RMM‐like index was used to compute an MJO climatology and document the occurrence of primary, continuing, and terminating MJO events in the skeleton model. The overall amount of MJO activity and event lengths compared reasonably well to observations for such a simple model. Attempts at reconciling the observed geographic distribution of individual MJO initiation and termination events were not successful for the stochastic simulations, though stochasticity is necessary in order to produce composite MJOs that initiate and decay with time scales similar to observations. Finally, analysis indicates that the existence of slow‐moving, eastward traveling waves with higher wave numbers (k ≈ 12) embedded within the large‐scale flow often precedes MJO termination in the skeleton model.

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“…[], with the sole exception that the zonal average of the radiative cooling term,

\overset{s^{θ} ((), x)}{true}

Section: Resultsmentioning

confidence: 89%

Evaluating MJO event initiation and decay in the skeleton model using an RMM‐like index

et al. 2015

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“…However, the main gain here is that the MJO mode exhibits a vertical structure with a westward vertical tilt in zonal wind, moisture, temperature, and diabatic heating, as observed in nature (Kiladis et al, 2005). Similarly to the coarser skeleton theory, a stochastic version for the multicloud skeleton theory is proposed and analyzed in Thual and Majda (2016). Nonlinear simulations with the refined skeleton theory produce similar time‐space spectra with a dominating MJO‐like signal on intraseasonal and planetary scales with the same level of intermittency and realism.…”

Section: Skeleton and Multiscale Theorymentioning

confidence: 99%

“…Together with the particular characteristic of its dispersion relation, the eastward low‐frequency mode as presented in Figures 2b and 2c replicates the two features listed above as a skeleton for the MJO, that is, most fundamental physical features of the MJO that can be captured by a simplest theory. As we will see below, by adding other dynamical processes to this theory (Majda & Stechmann, 2011), such as nonlinear dynamics, stochasticity, and refined vertical structure, additional features among those listed in section 2, such as intermittency, meridional asymmetry, and vertical tilt, can be captured by this multiscale MJO theory (Majda & Stechmann, 2011; Thual et al, 2014; Thual et al, 2015; Thual & Majda, 2015; Thual & Majda, 2016). Majda and Stechmann (2009) pointed out that while the theory presented here is called the MJO skeleton, the muscle for the MJO body comes from upscale (thermal and momentum) eddy fluxes due to synoptic‐scale waves (Biello & Majda, 2005; Majda & Biello, 2004).…”

Section: Skeleton and Multiscale Theorymentioning

confidence: 99%

Four Theories of the Madden‐Julian Oscillation

Zhang

Adames

Khouider

et al. 2020

Reviews of Geophysics

116

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Studies of the Madden‐Julian Oscillation (MJO) have progressed considerably during the past decades in observations, numerical modeling, and theoretical understanding. Many theoretical attempts have been made to identify the most essential processes responsible for the existence of the MJO. Criteria are proposed to separate a hypothesis from a theory (based on the first principles with quantitative and testable assumptions, able to predict quantitatively the fundamental scales and eastward propagation of the MJO). Four MJO theories are selected to be summarized and compared in this article: the skeleton theory, moisture‐mode theory, gravity‐wave theory, and trio‐interaction theory of the MJO. These four MJO theories are distinct from each other in their key assumptions, parameterized processes, and, particularly, selection mechanisms for the zonal spatial scale, time scale, and eastward propagation of the MJO. The comparison of the four theories and more recent development in MJO dynamical approaches lead to a realization that theoretical thinking of the MJO is diverse and understanding of MJO dynamics needs to be further advanced.

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“…For example, convective features and environmental atmospheric and oceanic characteristics during an active MJO event have been well documented [ Brown and Zhang , ; Yanai et al ., ; Houze et al ., ; Johnson and Ciesielski , ; Powell and Houze , , ; Xu and Rutledge , ; de Szoeke et al ., ]. Theoretical studies of the MJO [e.g., Raymond and Fuchs , ; Wang and Liu , ; Yang and Ingersoll , ; Thual and Majda , ; Adames and Kim , ] have generally sought a framework for explaining the low‐wave number convection and circulation signals associated with the MJO while over the warm pool. Widespread deep convection during an active MJO event over the warm pool elicits or reinforces a gravity wave‐like response with a half wavelength that is similar in size zonally to the entire warm pool [e.g., Knutson and Weickmann , ; Gottschalck et al ., ; Adames and Wallace , ; Powell and Houze , ].…”

Section: Introductionmentioning

confidence: 99%

Successive MJO propagation in MERRA‐2 reanalysis

Powell

2017

Geophysical Research Letters

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Composite circumnavigating Madden‐Julian oscillation (MJO) events in Version 2 of the NASA Modern Era Reanalysis for Research and Applications (MERRA‐2) reanalysis propagate as convectively coupled Kelvin waves over the Western Hemisphere and moisture waves like that described by Adames and Kim (2016) over the warm pool. Estimated zonally variable phase speeds of coupled Kelvin waves in the tropics are calculated by determining the “effective static stability” experienced by the wave. The wave is structured similarly to a classically derived deep tropospheric Kelvin wave, and its phase speed is up to 33 m s−1 or 40 m s−1 over the central/eastern Pacific or Atlantic/equatorial Africa, respectively, during boreal winter. Theoretically, estimated phase speeds of convectively coupled Kelvin waves over the tropical warm pool are greater than 15 m s−1, much faster than the propagation of the reanalyzed MJO. A complete theory for MJO propagation around the globe must allow both coupled Kelvin waves and moisture waves.

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A skeleton model for the MJO with refined vertical structure

Cited by 18 publications

References 38 publications

Evaluating MJO event initiation and decay in the skeleton model using an RMM‐like index

Evaluating MJO event initiation and decay in the skeleton model using an RMM‐like index

Four Theories of the Madden‐Julian Oscillation

Successive MJO propagation in MERRA‐2 reanalysis

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