A Reynolds-averaged turbulence modeling approach to the maintenance of the Venus superrotation

TL;DR

This paper introduces a Reynolds-averaged turbulence model with a nonlocal time scale to explain the maintenance of Venus's superrotation, demonstrating through simulations that the flow can be sustained by turbulence effects.

Contribution

It presents a novel turbulence modeling approach incorporating a nonlocal time scale to explain Venus's superrotation maintenance mechanism.

Findings

The model maintains superrotation in simulations.

Nonlocal turbulent viscosity enhances flow stability.

Vertical viscosity plays a crucial role in flow dynamics.

Abstract

A maintenance mechanism of an approximately linear velocity profile of the Venus zonal flow or superrotation is explored, with the aid of a Reynolds-averaged turbulence modeling approach. The basic framework is similar to that of Gierasch (1975) in the sense that the mechanism is examined under a given meridional circulation. The profile mimicking the observations of the flow is initially assumed, and its maintenance mechanism in the presence of turbulence effects is investigated from a viewpoint of the suppression of energy cascade. In the present work, the turbulent viscosity is regarded as an indicator of the intensity of the cascade. A novelty of this formalism is the use of the isotropic turbulent viscosity based on a nonlocal time scale linked to a large-scale flow structure. The mechanism is first discussed qualitatively. On the basis of these discussions, the two-dimensional numerical simulation of the proposed model is performed, with an initially assumed superrotation, and the fast zonal flow is shown to be maintained, compared with the turbulent viscosity lacking the nonlocal time scale. The relationship of the present model with the current general-circulation-model simulation is discussed in light of a crucial role of the vertical viscosity.