An improved moist‐convective rotating shallow‐water model and its application to instabilities of hurricane‐like vortices

Rostami, Masoud; Zeitlin, Vladimir

doi:10.1002/qj.3292

Cited by 21 publications

(21 citation statements)

References 34 publications

(54 reference statements)

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“…They showed that the equatorial modons keep their coherence in the moist-convective environment. Moreover, as is known, and confirmed in mcRSW [19,20], condensation leads to intensification of the cyclonic vortices. Correspondingly, the potential vorticity (PV) anomalies become stronger, the size smaller, and the phase speed of the convectively-coupled modon becomes higher than that of its adiabatic counterpart.…”

supporting

confidence: 58%

Eastward-moving convection-enhanced modons in shallow water in the equatorial tangent plane

Rostami

Zeitlin

2019

Physics of Fluids

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We report a discovery of steady long-living slowly eastward moving large-scale coherent twin cyclones, the equatorial modons, in the shallow water model in the equatorial beta-plane, the archetype model of the ocean and atmosphere dynamics in tropics. We start by constructing analytical asymptotic modon solutions in the non-divergent velocity approximation, and then show by simulations with a high-resolution numerical scheme that such configurations evolve into steady dipolar solutions of the full model. In the atmospheric context, the modons persist in the presence of moist convection, being accompanied and enhanced by specific patterns of water-vapour condensation.

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supporting

confidence: 58%

Eastward-moving convection-enhanced modons in shallow water in the equatorial tangent plane

Rostami

Zeitlin

2019

Physics of Fluids

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“…g = g(θ/θ 0 ) is effective gravity defined by the mean potential temperature of the atmospheric layer θ normalised by a reference value θ 0 , and f is the Coriolis parameter, h is the thickness of the layer defined as pseudo-height (note that the atmospheric shallow water model is "upside-down", in a sense that the free surface is on the ground and the fixed pseudo-height (pressure) level is on the top, while geopotential is constant on the ground, cf. (Bouchut et al, 2009;Rostami and Zeitlin, 2018),…”

Section: DVmentioning

confidence: 99%

On the role of spatially inhomogeneous diabatic effects upon the evolution of Mars’ annular polar vortex

Rostami

Zeitlin

Montabone

2018

Icarus

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The structure of Mars' annular polar vortex is not similar to that of its counterpart on Earth and is characterised by a potential vorticity (PV) low in the vicinity of the winter pole, rather than PV monotonically increasing towards the pole. A number of persistent asymmetric high-PV patches around the central low are also typical for the Martian polar vortex. The simplest vertically averaged model of the Mars atmosphere (a rotating shallow water model on the polar tangent plane) with inclusion of diabatic effects is used to get clues for understanding this surprising behaviour. The standard parameterisation of radiative relaxation is applied, together with a simple parameterisation of latent heat release due to spatially inhomogeneous CO 2 deposition. The parametrisation of inhomogeneous deposition is new in this type of models, and includes dependence on the concentration of condensation nuclei, which are considered as a passive tracer. Linear stability analysis of the zonally and time averaged Mars' winter polar vortex is performed, and thus identified unstable modes are used for initialisation of high-resolution numerical simulations of their nonlinear evolution in four different configurations (adiabatic, diabatic with only radiative relaxation, only deposition, and both radiative relaxation and deposition), in order to identify the role of each process.It is shown that the combined effect of radiative relaxation and inhomogeneous deposition can account for the observed, formally unstable structure of the polar vortex, including the patches of high potential vorticity.

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“…where M = h − γq is an analog of a moist static energy or moist enthalpy for the system. The above moist shallow water (MSW) equations are similar to those used by Bouchut et al (2009) and Rostami & Zeitlin (2018), although the implementation and the experiments, described below, significantly differ. Evaporation from a wet surface is parameterized by a bulk-aerodynamic-type formula,…”

Section: The Moist Shallow Water Equationsmentioning

confidence: 99%

Convective organization and eastward propagating equatorial disturbances in a simple excitable system

Vallis

Penn

2020

Quart J Royal Meteoro Soc

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We describe and illustrate a mechanism whereby convective aggregation and eastward propagating equatorial disturbances, similar in some respects to the Madden-Julian oscillation, arise. We construct a simple, explicit system consisting only of the shallow water equations plus a humidity variable; moisture enters via evaporation from a wet surface, is transported by the flow and removed by condensation, so providing a mass source to the height field. For a broad range of parameters the system is excitable and self-sustaining, even if linearly stable, with condensation producing convergence and gravity waves that, acting together, trigger more condensation. On the equatorial beta-plane the convection first aggregates near the equator, generating patterns related to those in the Matsuno-Gill problem. However, the pattern is unsteady and more convection is triggered on its eastern edge, leading to a precipitating disturbance that progresses eastward. The effect is enhanced by westward prevailing winds that increase the evaporation east of the disturbance. The pattern is confined to a region within a few deformation radii of equator because here the convection can best create the convergence needed to organize into a self-sustaining pattern. Formation of the disturbance preferentially occurs where the surface is warmer and sufficient time (a few tens of days) must pass before conditions arise that enable the disturbance to reform, as is characteristic both of excitable systems and the MJO itself. The speed of the disturbance depends on the efficiency of evaporation and the heat released by condensation, and is typically a few meters per second, much less than the Kelvin wave speed.

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An improved moist‐convective rotating shallow‐water model and its application to instabilities of hurricane‐like vortices

Cited by 21 publications

References 34 publications

Eastward-moving convection-enhanced modons in shallow water in the equatorial tangent plane

Eastward-moving convection-enhanced modons in shallow water in the equatorial tangent plane

On the role of spatially inhomogeneous diabatic effects upon the evolution of Mars’ annular polar vortex

Convective organization and eastward propagating equatorial disturbances in a simple excitable system

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