Mesoscale simulations of organized convection: Importance of convective equilibrium
TLDR
Clark et al. as discussed by the authors examined the hypothesis that a key feature determining the sensitivity to the environment is whether the forcing of convection is sufficiently homogeneous and slowly varying that the convection can be considered to be in equilibrium.Abstract:
The validity of convective parametrization breaks down at the resolution of mesoscale models, and the success of parametrized versus explicit treatments of convection is likely to depend on the large-scale environment. In this paper we examine the hypothesis that a key feature determining the sensitivity to the environment is whether the forcing of convection is sufficiently homogeneous and slowly varying that the convection can be considered to be in equilibrium. Two case studies of mesoscale convective systems over the UK, one where equilibrium conditions are expected and one where equilibrium is unlikely, are simulated using a mesoscale forecasting model. The time evolution of area-average convective available potential energy and the time evolution and magnitude of the timescale of convective adjustment are consistent with the hypothesis of equilibrium for case 1 and non-equilibrium for case 2.
For each case, three experiments are performed with different partitionings between parametrized and explicit convection: fully parametrized convection, fully explicit convection and a simulation with significant amounts of both. In the equilibrium case, bulk properties of the convection such as area-integrated rain rates are insensitive to the treatment of convection. However, the detailed structure of the precipitation field changes; the simulation with parametrized convection behaves well and produces a smooth field that follows the forcing region, and the simulation with explicit convection has a small number of localized intense regions of precipitation that track with the mid-levelflow. For the non-equilibrium case, bulk properties of the convection such as area-integrated rain rates are sensitive to the treatment of convection. The simulation with explicit convection behaves similarly to the equilibrium case with a few localized precipitation regions. In contrast, the cumulus parametrization fails dramatically and develops intense propagating bows of precipitation that were not observed. The simulations with both parametrized and explicit convection follow the pattern seen in the other experiments, with a transition over the duration of the run from parametrized to explicit precipitation. The impact of convection on the large-scaleflow, as measured by upper-level wind and potential-vorticity perturbations, is very sensitive to the partitioning of convection for both cases. © Royal Meteorological Society, 2006. Contributions by P. A. Clark and M. E. B. Gray are Crown Copyright.read more
Citations
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Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]
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References
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Journal ArticleDOI
Numerical Study of Convection Observed during the Winter Monsoon Experiment Using a Mesoscale Two-Dimensional Model
TL;DR: In this article, a two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea.
Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]
TL;DR: In this article, a two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea.
Journal ArticleDOI
Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I
Akio Arakawa,Wayne H. Schubert +1 more
TL;DR: In this paper, large-scale modification of the environment by cumulus clouds is discussed in terms of entrainment, detraining, evaporation, and subsidence, and budget equations for mass, static energy, water vapor, and liquid water are considered.
Journal ArticleDOI
Studies with a flexible new radiation code. I: Choosing a configuration for a large-scale model
J. M. Edwards,A. Slingo +1 more
TL;DR: In this article, a new radiation code based on the two-stream equations in both the long-wave and short-wave spectral regions is described, which is well suited to the investigation of the sensitivity of radiative calculations to changes in the way in which physical processes are parametrized.
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