J. Adv. Model. Earth Sys., submitted 2015.
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, 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 model, 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 more likely to exist at higher SST. In some models, the existence of multiple equilibria is sensitive to some parameters in the WTG calculations.