Intercomparison of methods of coupling between convection and large‐scale circulation: 1. Comparison over uniform surface conditions

Abstract

As part of an international intercomparison project, a set of single-column models (SCMs) and cloud-resolving models (CRMs) are run under the weak-temperature gradient (WTG) method and the damped gravity wave (DGW) method. For each model, the implementation of the WTG or DGW method involves a simulated column which is coupled to a reference state defined with profiles obtained from the same model in radiative-convective equilibrium. The simulated column has the same surface conditions as the reference state and is initialized with profiles from the reference state. We performed systematic comparison of the behavior of different models under a consistent implementation of the WTG method and the DGW method and systematic comparison of the WTG and DGW methods in models with different physics and numerics. CRMs and SCMs produce a variety of behaviors under both WTG and DGW methods. Some of the models reproduce the reference state while others sustain a large-scale circulation which results in either substantially lower or higher precipitation compared to the value of the reference state. CRMs show a fairly linear relationship between precipitation and circulation strength. SCMs display a wider range of behaviors than CRMs. Some SCMs under the WTG method produce zero precipitation. Within an individual SCM, a DGW simulation and a corresponding WTG simulation can produce different signed circulation. When initialized with a dry troposphere, DGW simulations always result in a precipitating equilibrium state. The greatest sensitivities to the initial moisture conditions occur for multiple stable equilibria in some WTG simulations, corresponding to either a dry equilibrium state when initialized as dry or a precipitating equilibrium state when initialized as moist. Multiple equilibria are seen in more WTG simulations for higher SST. In some models, the existence of multiple equilibria is sensitive to some parameters in the WTG calculations.

Modeling the Interaction between Quasigeostrophic Vertical Motion and Convection in a Single Column

“…Raymond (2007) tested a convective parameterization against a CRM in a modeling framework with parameterized large-scale dynamics-in that case, the WTG framework for the tropics. Indeed, recent model intercomparison studies (Daleu et al 2015, manuscript submitted to J. Adv. Model.…”

Forcings and feedbacks on convection in the 2010 Pakistan flood: Modeling extreme precipitation with interactive large‐scale ascent

“…This modeling framework extends the notion of ''parameterization of large-scale dynamics'' previously applied in the tropics-including the weak-temperature-gradient method [e.g., Sobel and Bretherton, 2000;Raymond and Zeng, 2005;Daleu et al, 2015], the damped-gravity-wave method [e.g., Kuang, 2008;Blossey et al, 2009;Romps, 2012;Daleu et al, 2015], and related others [e.g., Mapes, 2004;Bergman and Sardeshmukh, 2004]-to parameterize large-scale vertical motion. These methods allow attribution of precipitation to environmental factors such as the sea surface temperature (SST) or the large-scale tropospheric temperature profile, and have been used to aid understanding of a variety of phenomena in the tropics [e.g., Chiang and Sobel, 2002;Wang et al, 2013Wang et al, , 2015Nie and Sobel, 2015;Sessions et al, 2015].…”

A short review of numerical cloud-resolving models

“…In short, it consists in prescribing a temperature rather than a mean vertical velocity profile in the larger-scale advection term. Thus, in CRMs with periodic lateral boundary conditions, this translates into a mean temperature nudged towards a given profile, which in turns dictates the fluctuations of vertical advection (Raymond and Zeng, 2005;Daleu et al, 2015). In its simplest form it can be formulated in a CRM using periodic conditions as:…”

“…to prevent adjustment in the sub-cloud boundary layer). A joint, similar formulation for the large-scale advection of specific humidity (thus involving a reference profile for water vapour too) is sometimes introduced (Daleu et al, 2015).…”

“…More recently, the WTG framework, distinct from the CRE framework in the formulation of its boundary conditions (cf Section 4.5), was also used in CRMs to investigate climatic issues (in a RCE mode). A peculiar result arising from these studies is the existence of multiple equilibria for a given SST, with a final equilibrium, either dry vs. wet, largely controlled by the initial water vapour field (Sessions et al, 2010;Daleu et al, 2015). Ruppert (2016) also used the WTG framework to analyse the role of the diurnal cycle of radiation on convection and clouds.…”