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Andrew J. Majda - One of the best experts on this subject based on the ideXlab platform.
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Refined Vertical Structure in the Stochastic Skeleton Model for the MJO
Tropical Intraseasonal Variability and the Stochastic Skeleton Method, 2019Co-Authors: Andrew J. Majda, Samuel N. Stechmann, Shengqian Chen, H. Reed Ogrosky, Sulian ThualAbstract:To a first approximation, the Madden–Julian oscillation (MJO) has a symmetry (actually, an anti-symmetry) in its Vertical Structure: the winds in the upper troposphere are nearly equal in magnitude and opposite in sign to the winds in the lower troposphere. In earlier chapters of the book, such a Vertical Structure was used as a simplifying assumption in formulating the most basic versions of the MJO skeleton model. In the present chapter, more general versions of the skeleton model are described, and they incorporate deviations from this anti-symmetric Vertical Structure. The underlying processes that govern the Vertical Structure are a set of distinct cloud types.
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A skeleton model for the MJO with refined Vertical Structure
Climate Dynamics, 2015Co-Authors: Sulian Thual, Andrew J. MajdaAbstract:The Madden–Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on intraseasonal timescales and planetary spatial scales. The skeleton model is a minimal dynamical model that recovers robustly the most fundamental MJO features of (I) a slow eastward speed of roughly \(5\, {\mathrm{ms}}^{-1}\), (II) a peculiar dispersion relation with \(d\omega /dk \approx 0\), and (III) a horizontal quadrupole vortex Structure. This model depicts the MJO as a neutrally-stable atmospheric wave that involves a simple multiscale interaction between planetary dry dynamics, planetary lower-tropospheric moisture and the planetary envelope of synoptic-scale activity. Here we propose and analyse an extended version of the skeleton model with additional variables accounting for the refined Vertical Structure of the MJO in nature. The present model reproduces qualitatively the front-to-rear Vertical Structure of the MJO found in nature, with MJO events marked by a planetary envelope of convective activity transitioning from the congestus to the deep to the stratiform type, in addition to a front-to-rear Structure of moisture, winds and temperature. Despite its increased complexity the present model retains several interesting features of the original skeleton model such as a conserved energy and similar linear solutions. We further analyze a model version with a simple stochastic parametrization for the unresolved details of synoptic-scale activity. The stochastic model solutions show intermittent initiation, propagation and shut down of MJO wave trains, as in previous studies, in addition to MJO events with a front-to-rear Vertical Structure of varying intensity and characteristics from one event to another.
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A Suite of Skeleton Models for the MJO with Refined Vertical Structure
Mathematics of Climate and Weather Forecasting, 2015Co-Authors: Sulian Thual, Andrew J. MajdaAbstract:AbstractThe Madden-Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on intraseasonal timescales and planetary spatial scales. The skeleton model is a minimal dynamical model that recovers robustly the most fundamental MJO features of (I) a slow eastward speed of roughly 5 ms−1, (II) a peculiar dispersion relation with dw/dk ≈ 0, and (III) a horizontal quadrupole vortex Structure. This model depicts the MJO as a neutrally-stable atmosphericwave that involves a simple multiscale interaction between planetary dry dynamics, planetary lower-tropospheric moisture and the planetary envelope of synoptic-scale activity.Here we propose and analyze a suite of skeleton models that qualitatively reproduce the refined Vertical Structure of the MJO in nature. This Vertical Structure consists of a planetary envelope of convective activity transitioning from the congestus to the deep to the stratiform type, in addition to a front-to-rear (i.e. tilted) Structure of heating, moisture, winds and temperature. A first example of skeleton model achieving this goal has been considered recently in work by the authors. The construction of such a model satisfies an energy conservation principle, such that its solutions at the intraseasonal-planetary scale remain neutrally stable. Here, additional classes of skeleton models are constructed based on the same principle. In particular, those new models are more realistic then the former one as they consider fully coupled interactions between the planetary dry dynamics of the first and second baroclinic mode and the details of the Vertical Structure of moisture and convective activity. All models reproduce qualitatively the refined Vertical Structure of the MJO. In addition,when considered with a simple stochastic parametrization for the unresolved details of synopticscale activity, all models show intermittent initiation, propagation and shut down of MJO wave trains, as in previous studies.
Ib A Svendsen - One of the best experts on this subject based on the ideXlab platform.
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Vertical Structure of the undertow outside the surf zone
Journal of Geophysical Research, 1993Co-Authors: Uday Putrevu, Ib A SvendsenAbstract:The Vertical Structure of the undertow in the shoaling region outside the surf zone is quite different from that inside the surf zone. Inside the surf zone the undertow typically has a large seaward directed velocity near the bottom and either a shoreward directed or a small seaward directed velocity at trough level. Measurements show that outside the surf zone the undertow has a small seaward directed velocity near the bed and a large seaward directed velocity at trough level. In this paper we develop theoretical expressions for the undertow outside the surf zone and show that the steady streaming from the bottom boundary layer which was earlier found to have a negligible effect in the surf zone (Svendsen et al., 1987) does have a significant influence on the Vertical Structure of the undertow in that region.
Sulian Thual - One of the best experts on this subject based on the ideXlab platform.
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Refined Vertical Structure in the Stochastic Skeleton Model for the MJO
Tropical Intraseasonal Variability and the Stochastic Skeleton Method, 2019Co-Authors: Andrew J. Majda, Samuel N. Stechmann, Shengqian Chen, H. Reed Ogrosky, Sulian ThualAbstract:To a first approximation, the Madden–Julian oscillation (MJO) has a symmetry (actually, an anti-symmetry) in its Vertical Structure: the winds in the upper troposphere are nearly equal in magnitude and opposite in sign to the winds in the lower troposphere. In earlier chapters of the book, such a Vertical Structure was used as a simplifying assumption in formulating the most basic versions of the MJO skeleton model. In the present chapter, more general versions of the skeleton model are described, and they incorporate deviations from this anti-symmetric Vertical Structure. The underlying processes that govern the Vertical Structure are a set of distinct cloud types.
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A skeleton model for the MJO with refined Vertical Structure
Climate Dynamics, 2015Co-Authors: Sulian Thual, Andrew J. MajdaAbstract:The Madden–Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on intraseasonal timescales and planetary spatial scales. The skeleton model is a minimal dynamical model that recovers robustly the most fundamental MJO features of (I) a slow eastward speed of roughly \(5\, {\mathrm{ms}}^{-1}\), (II) a peculiar dispersion relation with \(d\omega /dk \approx 0\), and (III) a horizontal quadrupole vortex Structure. This model depicts the MJO as a neutrally-stable atmospheric wave that involves a simple multiscale interaction between planetary dry dynamics, planetary lower-tropospheric moisture and the planetary envelope of synoptic-scale activity. Here we propose and analyse an extended version of the skeleton model with additional variables accounting for the refined Vertical Structure of the MJO in nature. The present model reproduces qualitatively the front-to-rear Vertical Structure of the MJO found in nature, with MJO events marked by a planetary envelope of convective activity transitioning from the congestus to the deep to the stratiform type, in addition to a front-to-rear Structure of moisture, winds and temperature. Despite its increased complexity the present model retains several interesting features of the original skeleton model such as a conserved energy and similar linear solutions. We further analyze a model version with a simple stochastic parametrization for the unresolved details of synoptic-scale activity. The stochastic model solutions show intermittent initiation, propagation and shut down of MJO wave trains, as in previous studies, in addition to MJO events with a front-to-rear Vertical Structure of varying intensity and characteristics from one event to another.
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A Suite of Skeleton Models for the MJO with Refined Vertical Structure
Mathematics of Climate and Weather Forecasting, 2015Co-Authors: Sulian Thual, Andrew J. MajdaAbstract:AbstractThe Madden-Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on intraseasonal timescales and planetary spatial scales. The skeleton model is a minimal dynamical model that recovers robustly the most fundamental MJO features of (I) a slow eastward speed of roughly 5 ms−1, (II) a peculiar dispersion relation with dw/dk ≈ 0, and (III) a horizontal quadrupole vortex Structure. This model depicts the MJO as a neutrally-stable atmosphericwave that involves a simple multiscale interaction between planetary dry dynamics, planetary lower-tropospheric moisture and the planetary envelope of synoptic-scale activity.Here we propose and analyze a suite of skeleton models that qualitatively reproduce the refined Vertical Structure of the MJO in nature. This Vertical Structure consists of a planetary envelope of convective activity transitioning from the congestus to the deep to the stratiform type, in addition to a front-to-rear (i.e. tilted) Structure of heating, moisture, winds and temperature. A first example of skeleton model achieving this goal has been considered recently in work by the authors. The construction of such a model satisfies an energy conservation principle, such that its solutions at the intraseasonal-planetary scale remain neutrally stable. Here, additional classes of skeleton models are constructed based on the same principle. In particular, those new models are more realistic then the former one as they consider fully coupled interactions between the planetary dry dynamics of the first and second baroclinic mode and the details of the Vertical Structure of moisture and convective activity. All models reproduce qualitatively the refined Vertical Structure of the MJO. In addition,when considered with a simple stochastic parametrization for the unresolved details of synopticscale activity, all models show intermittent initiation, propagation and shut down of MJO wave trains, as in previous studies.
Uday Putrevu - One of the best experts on this subject based on the ideXlab platform.
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Vertical Structure of the undertow outside the surf zone
Journal of Geophysical Research, 1993Co-Authors: Uday Putrevu, Ib A SvendsenAbstract:The Vertical Structure of the undertow in the shoaling region outside the surf zone is quite different from that inside the surf zone. Inside the surf zone the undertow typically has a large seaward directed velocity near the bottom and either a shoreward directed or a small seaward directed velocity at trough level. Measurements show that outside the surf zone the undertow has a small seaward directed velocity near the bed and a large seaward directed velocity at trough level. In this paper we develop theoretical expressions for the undertow outside the surf zone and show that the steady streaming from the bottom boundary layer which was earlier found to have a negligible effect in the surf zone (Svendsen et al., 1987) does have a significant influence on the Vertical Structure of the undertow in that region.
Aldo Frezzotti - One of the best experts on this subject based on the ideXlab platform.
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DSMC simulation of the Vertical Structure of planetary rings
Astronomy and Astrophysics, 2001Co-Authors: Aldo FrezzottiAbstract:A statistical Monte Carlo method (DSMC) is developed to simulate granular flows occurring in dense planetary rings. The accuracy of the method is assessed through a comparison with existing molecular dynamics simulations of the Vertical Structure of planetary rings with and without self-gravity eects.
