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Departures from convective equilibrium with a rapidly-varying surface forcing

Davies, L., Plant, R. S. ORCID: and Derbyshire, S. H. (2013) Departures from convective equilibrium with a rapidly-varying surface forcing. Quarterly Journal of the Royal Meteorological Society, 139 (676). pp. 1731-1746. ISSN 1477-870X

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To link to this item DOI: 10.1002/qj.2065


Convective equilibrium is a long-standing and useful concept for understanding many aspects of the behaviour of deep moist convection. For example, it is often invoked in developing parameterizations for large-scale models. However, the equilibrium assumption may begin to break down as models are increasingly used with shorter timesteps and finer resolutions. Here we perform idealized cloud-system resolving model simulations of deep convection with imposed time variations in the surface forcing. A range of rapid forcing timescales from 1 − 36hr are used, in order to induce systematic departures from equilibrium. For the longer forcing timescales, the equilibrium assumption remains valid, in at least the limited sense that cycle-integrated measures of convective activity are very similar from cycle to cycle. For shorter forcing timescales, cycle-integrated convection becomes more variable, with enhanced activity on one cycle being correlated with reduced activity on the next, suggesting a role for convective memory. Further investigation shows that the memory does not appear to be carried by the domain-mean thermodynamic fields but rather by structures on horizontal scales of 5 − 20km. Such structures are produced by the convective clouds and can persist beyond the lifetime of the cloud, even through to the next forcing cycle.

Item Type:Article
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:30996
Uncontrolled Keywords:cloud-resolving modelling; convective quasi-equilibrium; rapid forcing
Publisher:Royal Meteorological Society
Publisher Statement:This is a preprint of an article accepted for publication in the Quarterly Journal of the Royal Meteorological Society. Copyright 2013 Royal Meteorological Society.


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