Universität zu Köln

Brast, Maren (2017). Scale-adaptive Parameterization of Shallow Cumulus Convection. PhD thesis, Universität zu Köln.

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Abstract

The representation of cumulus clouds in general circulation models is achieved through parameterization schemes. For numerical weather prediction models, the resolutions are getting smaller and reaching the point at which boundary layer clouds can become partially resolved. In this case, the parameterization should only represent those clouds that cannot be resolved by the model. In the first part of this study, the behavior of the standard rising plume model is investigated by feeding a rising plume model with data from a large-eddy simulation (LES) of a shallow convective cloud field. Bulk statistics of ensembles of rising parcels as well as individual parcels are examined, and the impact of the entrainment formulation on the fate of the plume is investigated. It is found that the local environment is more important in determining the behavior of the parcel than the entrainment formulation. The next step is to explore the scale-adaptivity of a multi-plume parameterization scheme for vertical transport in the shallow convective boundary layer (ED(MF)^n), which is formulated in terms of discretized size distributions. This scheme is implemented into an LES model, replacing the original subgrid scheme. Sensitivity tests for the horizontal resolution should reveal at what range of resolutions the gray zone for vertical transport in the boundary layer is situated. For an idealized case study of shallow cumulus clouds it is found that for high resolutions the parameterization scheme does not add much transport. For coarser resolutions, it slowly takes over the transport by the clouds, until for the coarsest resolution all clouds are subgrid and represented by ED(MF)^n. In the last study the parameterization scheme is tested for a more complex situation, where the LES is evaluated with measurements. Though these cases are more challenging, the behavior of ED(MF)^n in the gray zone as documented for the idealized case over the ocean is reproduced.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Brast, Maren brast@meteo.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-77187
Date:	8 May 2017
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Earth sciences
Uncontrolled Keywords:	Keywords Language Parameterization English Shallow cumulus clouds English Large-eddy simulation English
Date of oral exam:	30 June 2017
Referee:	Name Academic Title Neggers, Roel Prof. Dr. Crewell, Susanne Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/7718