A Density Current Parameterization Coupled with Emanuel’s Convection Scheme. Part I: The Models

Abstract

The aim of the present series of papers is to develop a density current parameterization for global circulation models. This first paper is devoted to the presentation of this new wake parameterization coupled with Emanuel's convective scheme. The model represents a population of identical circular cold pools (the wakes) with vertical frontiers. The wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts. The budget equations for mass, energy, and water yield evolution equations for the prognostic variables (the vertical profiles of the temperature and humidity differences between the wakes and their exterior). They also provide additional terms for the equations of the mean variables. The driving terms of the wake equations are the differential heating and drying due to convective drafts. The action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precipitating downdrafts to the wake region and the effect of the saturated drafts to their exterior. Conversely, the action of the wakes on convection is implemented by introducing two new variables representing the convergence at the leading edge of the wakes. The available lifting energy (ALE) determines the triggers of deep convection: convection occurs when ALE exceeds the convective inhibition. The available lifting power (ALP) determines the intensity of convection; it is equal to the power input into the system by the collapse of the wakes. The ALE/ALP closure, together with the splitting of the convective heating and drying, implements the full coupling between wake and convection. The coupled wake-convection scheme thus created makes it possible to represent the moist convective processes more realistically, to prepare the coupling of convection with boundary layer and orographic processes, and to consider simulating the propagation of convective systems.

The Formation of Wider and Deeper Clouds as a Result of Cold-Pool Dynamics

“…Several successful attempts have been undertaken to include the effects of cold pools into parameterization schemes (e.g., Qian et al 1998;Mapes 2000;Rio et al 2009;Grandpeix and Lafore 2010;Hohenegger and Bretherton 2011). In these approaches the focus has been on the wakes of the cold pools and the associated dynamical triggering.…”

Parameterization of convective transport in the boundary layer and its impact on the representation of the diurnal cycle of wind and dust emissions

“…hel (Parker et al, 2005;Lothon et al, 2008;Guichard et al, 2009;Schepanski et al, 2009). This maximum is associated with the low-level jet which forms at a few hundred meters above the surface after sunset, when the near-surface boundary layer turbulence collapses (see e.g., Bain et al, 2010;Gounou et al, 2012;Fiedler et al, 2013).…”

“…We show here how the activation of the thermal plume model leads to a better representation of the diurnal cycle of near-surface winds -even better than in current meteorological reanalyses -and how this better representation reinforces surface emissions drastically. We focus here on emissions during the dry season while a companion paper will be devoted to the representation of dust emission by gusts associated with convection-generated cold pools, for which a specific parameterization has also been introduced in LMDZ (Grandpeix and Lafore, 2010;Rio et al, 2009).…”

A Parameterization of Convective Dust Storms for Models with Mass-Flux Convection Schemes

“…A parameterization of propagating subgrid cold pools therefore requires the complete coupling with the parameterization of subgrid convection (Grandpeix and Lafore 2010). Such a coupling is beyond the scope of our work.…”