Moist versus Dry Barotropic Instability in a Shallow-Water Model of the Atmosphere with Moist Convection

Abstract

Dynamical influence of moist convection upon development of the barotropic instability is studied in the rotating shallow-water model. First, an exhaustive linear ''dry'' stability analysis of the Bickley jet is performed, and the most unstable mode identified in this way is used to initialize simulations to compare the development and the saturation of the instability in dry and moist configurations. High-resolution numerical simulations with a well-balanced finite-volume scheme reveal substantial qualitative and quantitative differences in the evolution of dry and moist-convective instabilities. The moist effects affect both balanced and unbalanced components of the flow. The most important differences between dry and moist evolution are 1) the enhanced efficiency of the moist-convective instability, which manifests itself by the increase of the growth rate at the onset of precipitation, and by a stronger deviation of the end state from the initial one, measured with a number of different norms; 2) a pronounced cyclone-anticyclone asymmetry during the nonlinear evolution of the moist-convective instability, which leads to an additional, with respect to the dry case, geostrophic adjustment, and the modification of the end state; and 3) an enhanced ageostrophic activity in the precipitation zones but also in the nonprecipitating areas because of the secondary geostrophic adjustment.

Moist versus Dry Baroclinic Instability in a Simplified Two-Layer Atmospheric Model with Condensation and Latent Heat Release

“…We use a moist-convective twolayer rotating shallow-water (mc2RSW) model recently developed and tested in Lambaerts et al (2011b). It represents the atmosphere as a moist lower layer and a dry upper layer with mass and momentum exchanges due to moist convection.…”

“…Layered atmospheric models of this type with moist physics were previously considered in the literature: Gill (1982) and Frierson et al (2004) worked with the linear baroclinic rotating shallow-water (RSW)-type of model, Lapeyre and Held (2004) studied a quasigeostrophic model, and Bouchut et al (2009) studied the one-layer mcRSW model. We should stress that all of these previously considered models can be derived from the mc2RSW model in specific limits (Lambaerts et al 2011b). The mc2RSW model is fully nonlinear, takes into account the ageostrophic motions, and couples the moisture evolution with dynamics via condensation and latent heat release.…”

“…We follow the same strategy as Lambaerts et al (2011a), who studied the influence of moisture on barotropic instability: after performing a detailed linear stability analysis of the dry basic configuration, we extract the most unstable mode and initialize the direct numerical simulations of nonlinear saturation with this mode. We perform parallel numerical simulations, with the condensation switched off and on.…”

Geophysical fluid dynamics: whence, whither and why?

“…Evidently, nonlinearities and feedback abound, as well as a mathematical stiffness, and understanding moist effects is a challenge both for numerical modellers and for theoretical dynamicists. It is hardly original to say that folding moisture into a GFD framework is a challenging and important problem, for much work has already taken place-see [81][82][83][84][85][86] for miscellaneous examples and reviews-but it is a true statement nevertheless.…”

Convection of Moist Saturated Air: Analytical Study

“…Investigation and understanding of atmospheric convection is of great importance for the development and improvement of global weather and climate prediction [3,4]. Convection interacts with the larger-scale dynamics of planetary atmospheres in ways that remain poorly represented in global models [5,6]. The important role in the convective instability is played by the release of latent heat of condensation during phase transitions of water vapor in the moist saturated air [7].…”