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Titel |
High-resolution WRF-LES simulations for real episodes: A case study for prealpine terrain |
VerfasserIn |
Cornelius Hald, Matthias Mauder, Patrick Laux, Harald Kunstmann |
Konferenz |
EGU General Assembly 2017
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250148203
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Publikation (Nr.) |
EGU/EGU2017-12439.pdf |
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Zusammenfassung |
While in most large or regional scale weather and climate models turbulence is parametrized,
LES (Large Eddy Simulation) allows for the explicit modeling of turbulent structures in the
atmosphere. With the exponential growth in available computing power the technique has
become more and more applicable, yet it has mostly been used to model idealized
scenarios.
It is investigated how well WRF-LES can represent small scale weather patterns. The results
are evaluated against different hydrometeorological measurements.
We use WRF-LES to model the diurnal cycle for a 48 hour episode in summer over
moderately complex terrain in southern Germany. The model setup uses a high resolution
digital elevation model, land use and vegetation map. The atmospheric boundary conditions
are set by reanalysis data. Schemes for radiation and microphysics and a land-surface model
are employed.
The biggest challenge in modeling arises from the high horizontal resolution of dx = 30m,
since the subgrid-scale model then requires a vertical resolution dz ≈ 10m for optimal
results. We observe model instabilities and present solutions like smoothing of the surface
input data, careful positioning of the model domain and shortening of the model time step
down to a twentieth of a second.
Model results are compared to an array of various instruments including eddy covariance
stations, LIDAR, RASS, SODAR, weather stations and unmanned aerial vehicles. All
instruments are part of the TERENO pre-Alpine area and were employed in the orchestrated
measurement campaign ScaleX in July 2015.
Examination of the results show reasonable agreement between model and measurements in
temperature- and moisture profiles. Modeled wind profiles are highly dependent on the
vertical resolution and are in accordance with measurements only at higher wind speeds. A
direct comparison of turbulence is made difficult by the purely statistical character of
turbulent motions in the model. |
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