Two-dimensional Moist Stratified Turbulence and the Emergence of Vertically Sheared Horizontal Flows

TL;DR

This study investigates moist stratified turbulence in a 2D Boussinesq system, revealing the emergence of vertically sheared horizontal flows and moist balance states through numerical simulations and asymptotic analysis.

Contribution

It introduces a simplified 2D moist turbulence model demonstrating the formation of moist balance and vertically sheared horizontal flows, supported by numerical and asymptotic analysis.

Findings

Emergence of ordered moist turbulent structures with power-law spectral scaling.

Development of moist balance characterized by hydrostatic, saturated, vertically sheared horizontal flow.

Transition to moist balance or sustained oscillations depending on initial water content.

Abstract

Moist stratified turbulence is studied in a two-dimensional Boussinesq system influenced by condensation and evaporation. The problem is set in a periodic domain and employs simple evaporation and condensation schemes, wherein both the processes push parcels towards saturation. Numerical simulations demonstrate the emergence of a moist turbulent state consisting of ordered structures with a clear power-law type spectral scaling from initially spatially uncorrelated conditions. An asymptotic analysis in the limit of rapid condensation and strong stratification shows that, for initial conditions with enough water substance to saturate the domain, the equations support a straightforward state of moist balance characterized by a hydrostatic, saturated, vertically sheared horizontal flow (VSHF). For such initial conditions, by means of long time numerical simulations, the emergence of moist balance is verified. Specifically, starting from uncorrelated data, subsequent to the development of a moist turbulent state, the system experiences a rather abrupt transition to a regime which is close to saturation and dominated by a strong VSHF. On the other hand, initial conditions which do not have enough water substance to saturate the domain, do not attain moist balance. Rather, the system remains in a turbulent state and oscillates about moist balance. Even though balance is not achieved with these general initial conditions, the time scale of oscillation about moist balance is much larger than the imposed time scale of condensation and evaporation, thus indicating a distinct dominant slow component in the moist stratified two-dimensional turbulent system.