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Mesoscale simulations of organized convection: Importance of convective equilibrium

Done, J.M. and Craig, G. C. and Gray, S. L. and Clark, P.A. and Gray, M.E.B (2006) Mesoscale simulations of organized convection: Importance of convective equilibrium. Quarterly Journal of the Royal Meteorological Society, 132, pp. 737-756. DOI: 10.1256/qj.04.84.

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Official URL: http://www3.interscience.wiley.com/cgi-bin/jtoc/113388514/

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-level flow. 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-scale flow, as measured by upper-level wind and potential-vorticity perturbations, is very sensitive to the partitioning of convection for both cases.

Document Type:Article
Title:Mesoscale simulations of organized convection: Importance of convective equilibrium
Authors:
AuthorsInstitution or Email of Authors
Done, J.M.Univ. of Reading, Reading, UK
Craig, G. C.UNSPECIFIED
Gray, S. L.Univ. of Reading, Reading, UK
Clark, P.A.Univ. of Reading, Reading, UK
Gray, M.E.BMet Office, Exeter, UK
Date:2006
Journal or Publication Title:Quarterly Journal of the Royal Meteorological Society
Refereed publication:Yes
In ISI Web of Science:Yes
Volume:132
DOI:10.1256/qj.04.84
Page Range:pp. 737-756
Status:Published
Keywords:convective parametrization, explicit convection, precipitation
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben Atmosphären- und Klimaforschung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Cloud Physics and Traffic Meteorology
Deposited By: Jana Freund
Deposited On:12 Sep 2007
Last Modified:15 Jan 2010 00:00

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