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Designs for representing shear-induced cloud field organization in a convection parametrization scheme

Muetzelfeldt, M. ORCID: https://orcid.org/0000-0002-6851-7351 (2020) Designs for representing shear-induced cloud field organization in a convection parametrization scheme. PhD thesis, University of Reading

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Abstract/Summary

The mesoscale organization of tropical convection is an important atmospheric phenomenon, which often goes untreated in Convection Parametrization Schemes (CPSs). A methodology for designing changes to CPSs so that they can represent some aspects of shear-induced organization is developed. A novel clustering procedure is used to produce a set of 10 Representative Wind Profiles (RWPs) based on wind profiles from a climate model. The RWPs are found to be associated with the organization of convection. Idealized radiative-convective equilibrium experiments with a cloud-resolving model are performed. The wind profiles in the experiments are varied to investigate the effect of shear and surface wind on the cloud field and mean atmospheric state. Convection is stimulated by prescribed cooling in forcing experiments, and by relaxation back to a reference state in relaxation experiments. From the forcing experiments we find that organization and cloud lifetimes are dependent on shear, and that thermodynamic properties of the atmosphere show some dependence on surface wind. A robust relationship between the low-level shear and the organization of the cloud field is found. Relationships between the organization and both the mean lifetime of clouds, and the mean mass flux per cloud are also found. The Convective Available Potential Energy (CAPE) is found to be related to the surface wind. Relaxation experiments provide information about the convective response as a function of the imposed wind profile. Contrary to our expectations, the organized convective response is found to produce upper-level cooling and lower-level heating. We determine that this is due to the CAPE in the reference profiles, and the need to maintain a fixed thermodynamic profile. The results are used to design changes to existing CPSs to make them “shear-aware”. Methods for assessing the “shear-aware” schemes, and their representation of organization, are also discussed.

Item Type:Thesis (PhD)
Thesis Supervisor:Plant, B. and Clark, P.
Thesis/Report Department:Department of Meteorology
Identification Number/DOI:
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:96182
Date on Title Page:October 2019

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