Intercomparison of methods of coupling between convection and large-scale circulation: 2. Comparison over nonuniform surface conditions.

C L Daleu,P Peyrille,L Van Ulft,A Cheng,G Bellon,D Kim,A Sobel,M J Herman,F Ferry,S J Woolnough,S Sessions,S Wang,R S Plant,P Siebesma

doi:10.1002/2015ms000570

Abstract

As part of an international intercomparison project, the weak temperature gradient (WTG) and damped gravity wave (DGW) methods are used to parameterize large‐scale dynamics in a set of cloud‐resolving models (CRMs) and single column models (SCMs). The WTG or DGW method is implemented using a configuration that couples a model to a reference state defined with profiles obtained from the same model in radiative‐convective equilibrium. We investigated the sensitivity of each model to changes in SST, given a fixed reference state. We performed a systematic comparison of the WTG and DGW methods in different models, and a systematic comparison of the behavior of those models using the WTG method and the DGW method. The sensitivity to the SST depends on both the large‐scale parameterization method and the choice of the cloud model. In general, SCMs display a wider range of behaviors than CRMs. All CRMs using either the WTG or DGW method show an increase of precipitation with SST, while SCMs show sensitivities which are not always monotonic. CRMs using either the WTG or DGW method show a similar relationship between mean precipitation rate and column‐relative humidity, while SCMs exhibit a much wider range of behaviors. DGW simulations produce large‐scale velocity profiles which are smoother and less top‐heavy compared to those produced by the WTG simulations. These large‐scale parameterization methods provide a useful tool to identify the impact of parameterization differences on model behavior in the presence of two‐way feedback between convection and the large‐scale circulation.

Highlights

A key issue in understanding the tropical climate and its variability is the understanding of the two-way interaction between tropical deep convection and large-scale tropical circulations
The results presented in Daleu et al [2015], and in other previous studies [e.g., Sobel et al, 2007; Sessions et al, 2010] show that some single column models (SCMs) and cloudresolving models (CRMs) using the weak temperature gradient (WTG) method can sustain either a dry equilibrium state or a precipitating equilibrium state, given sufficiently different initial moisture conditions
To provide a more quantitative evaluation of the WTG and damped gravity wave (DGW) simulations, we calculated the ratio of mean precipitation rate in the simulated column, P, to the value of the corresponding radiative-convective equilibrium (RCE) reference state, PRef

Summary

Introduction

A key issue in understanding the tropical climate and its variability is the understanding of the two-way interaction between tropical deep convection and large-scale tropical circulations. Many single column model (SCM) and cloud-resolving model (CRM) studies have simulated the interactions of tropical deep convection with a prescribed large-scale flow, possibly based on idealization or experimental campaign [e.g., Tompkins, 2001; Xu et al, 2002; Derbyshire et al, 2004; Petch et al, 2006]. In such studies, the time scale characterizing changes in convection is assumed to be short compared to the time scale characterizing changes in the large-scale flow. The precipitation rates produced are too much constrained due to the predefined large-scale moisture advection [Mapes, 1997; Sobel and Bretherton, 2000] and such simulations

Objectives

Results

Conclusion