Universität zu Köln

Scale-adaptive Parameterization of Shallow Cumulus Convection

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

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    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)
    Brast, Marenbrast@meteo.uni-koeln.de
    URN: urn:nbn:de:hbz:38-77187
    Subjects: Earth sciences
    Uncontrolled Keywords:
    Shallow cumulus cloudsEnglish
    Large-eddy simulationEnglish
    Faculty: Mathematisch-Naturwissenschaftliche Fakultät
    Divisions: Mathematisch-Naturwissenschaftliche Fakultät > Institut für Geophysik und Meteorologie
    Language: English
    Date: 08 May 2017
    Date Type: Publication
    Date of oral exam: 30 June 2017
    Full Text Status: Public
    Date Deposited: 04 Aug 2017 09:39:49
    NameAcademic Title
    Neggers, RoelProf. Dr.
    Crewell, SusanneProf. Dr.
    URI: http://kups.ub.uni-koeln.de/id/eprint/7718

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