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

M Rostami,V Zeitlin

doi:10.1063/1.5080415

Abstract

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.

Highlights

Where ∇ = (∂x, ∂y), v = (u, v), u is zonal and v- meridional components of velocity, h is 52 geopotential height, β is the meridional gradient of the Coriolis parameter, and zis a unit vertical vector
The interpretation of the model in the oceanic context is direct, while in the atmospheric context it should be understood as vertically averaged primitive equations in pseudo-height pressure coordinates [16], and can be extended to include water vapor with condensation and related latent heat release [17], as well as surface evaporation
Velocity is much smaller than the phase velocity of the Kelvin waves c = gH, the nondimensional equations take the form:

Summary

Introduction

We construct the modon solutions in this regime and, following [6], use these asymptotic solutions to initialize high-resolution numerical simulations with the full RSW model, and show that coherent dipolar steady eastward-moving structures do arise and persist. In the atmospheric context, inclusion of moisture, with condensation and evaporation, enhances the modons, without disrupting long-time coherence, and produces specific convective patterns.

Results

Conclusion