J. Adv. Model. Earth Sys., submitted 2015.

Intercomparison of methods of coupling between convection and large-scale circulation. Part II: Comparison over non-uniform surface conditions.

Chimene L. Daleu, Steven J. Woolnough, Robert S. Plant
Department of Meteorology, University of Reading, Reading, UK

Sharon Sessions, Michael J. Herman
Department of Physics, New Mexico Tech, Socorro, NM, USA.

Adam H. Sobel
Department of Applied Physics and Applied Mathematics, and Lamont-Doherty Earth Observatory, Columbia University, New York, NY.

Shuguang Wang
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY.

Daehyun Kim
Department of Atmospheric Sciences, University of Washington, Seattle WA.

A. Cheng, G. Bellon, P. Peyrille, F. Ferry, A. P. Siebesma, B. Van Ulft
Other institutions.

Abstract

As part of an international intercomparison project, the two-way interaction between convection and large-scale dynamics is studied in a set of single column models (SCMs) and cloud-resolving models (CRMs) using two large-scale parameterization methods: 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. In Part 1 of this study, the simulated column has the same sea surface temperature (SST) as the reference state. In this paper, the reference state is held fixed while the SST in the simulated column is varied. For each value of SST, we performed two sets of systematic comparisons: a comparison of the WTG and DGW methods with a consistent implementation in models with different physics and numerics, and a comparison of the behavior of those models using the same large-scale parameterization method.

The sensitivity of precipitation rate to the SST differs from model to model and also depends on whether the WTG or DGW method is used to parameterize the large scale circulation. In general, SCMs display a wider range of behaviors than CRMs. CRMs show a fairly linear relationship between precipitation and circulation strength, but a few SCMs deviate from this linear relationship. All CRMs using either the WTG or DGW method show a nonlinear increase of mean precipitation rate with SST. In contrast, SCMs show sensitivities 26 of the mean precipitation rate to the SST which are not always monotonic. Within an individual SCM, a WTG simulation and a cor28 responding DGW simulation can produce different signs of the circulation. In general, DGW simulations produce large-scale pressure velocity profiles which are smoother and less top-heavy compared to those produced by the WTG simulations.

Consistent with observations and other numerical model studies, precipitation rate increases with column-relative humidity. A large proportion of the models show a rapid increase of mean precipitation rate when column35 relative humidity increases pass a threshold value. CRMs using either the WTG or DGW method show very similar relationships between mean precipitation rate and column-relative humidity, while SCMs exhibit a much wider range of behaviors.