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| Titel |
Sensitivity of the WRF model to PBL parametrisations and nesting techniques: evaluation of wind storms over complex terrain |
| VerfasserIn |
J. J. Gómez-Navarro, C. C. Raible, S. Dierer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 10 ; Nr. 8, no. 10 (2015-10-22), S.3349-3363 |
| Datensatznummer |
250116611
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| Publikation (Nr.) |
 copernicus.org/gmd-8-3349-2015.pdf |
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| Zusammenfassung |
| Simulating surface wind over complex terrain is a challenge in regional
climate modelling. Therefore, this study aims at identifying a set-up of the
Weather Research and Forecasting Model (WRF) model that minimises systematic
errors of surface winds in hindcast simulations. Major factors of the model
configuration are tested to find a suitable set-up: the horizontal
resolution, the planetary boundary layer (PBL) parameterisation scheme and
the way the WRF is nested to the driving data set. Hence, a number of
sensitivity simulations at a spatial resolution of 2 km are carried out and
compared to observations. Given the importance of wind storms, the analysis
is based on case studies of 24 historical wind storms that caused great
economic damage in Switzerland. Each of these events is downscaled using
eight different model set-ups, but sharing the same driving data set. The
results show that the lack of representation of the unresolved topography
leads to a general overestimation of wind speed in WRF. However, this bias
can be substantially reduced by using a PBL scheme that explicitly considers
the effects of non-resolved topography, which also improves the spatial
structure of wind speed over Switzerland. The wind direction, although
generally well reproduced, is not very sensitive to the PBL scheme. Further
sensitivity tests include four types of nesting methods: nesting only at the
boundaries of the outermost domain, analysis nudging, spectral nudging, and
the so-called re-forecast method, where the simulation is frequently
restarted. These simulations show that restricting the freedom of the model
to develop large-scale disturbances slightly increases the temporal agreement
with the observations, at the same time that it further reduces the
overestimation of wind speed, especially for maximum wind peaks. The model
performance is also evaluated in the outermost domains, where the resolution
is coarser. The results demonstrate the important role of horizontal
resolution, where the step from 6 to 2 km significantly improves model
performance. In summary, the combination of a grid size of 2 km, the
non-local PBL scheme modified to explicitly account for non-resolved
orography, as well as analysis or spectral nudging, is a superior combination
when dynamical downscaling is aimed at reproducing real wind fields. |
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