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Ann. Geophys., 24, 1537-1549, 2006
www.ann-geophys.net/24/1537/2006/
© European Geosciences Union 2006
Thermally driven circulation in a region of complex topography: comparison of wind-profiling radar measurements and MM5 numerical predictions
L. Bianco, B. Tomassetti, E. Coppola, A. Fracassi, M. Verdecchia, and G. Visconti
Centre of Excellence – CETEMPS, University of L’Aquila, L’Aquila, Italy
Abstract. The diurnal variation of regional wind patterns in the complex terrain of
Central Italy was investigated for summer fair-weather conditions and
winter time periods using a radar wind profiler. The profiler is located on
a site where interaction between the complex topography and land-surface
produces a variety of thermally and dynamically driven wind systems. The
observational data set, collected for a period of one year, was used first to
describe the diurnal evolution of thermal driven winds, second to validate
the Mesoscale Model 5 (MM5) that is a three-dimensional numerical model.
This type of analysis was focused on the near-surface wind observation,
since thermally driven winds occur in the lower atmosphere. According to the
valley wind theory expectations, the site – located on the left sidewall of
the valley (looking up valley) – experiences a clockwise turning with time.
Same characteristics in the behavior were established in both the
experimental and numerical results.
Because the thermally driven flows can have some depth and may be influenced
mainly by model errors, as a third step the analysis focuses on a subset of
cases to explore four different MM5 Planetary Boundary Layer (PBL)
parameterizations. The reason is to test how the results are sensitive to
the selected PBL parameterization, and to identify the better
parameterization if it is possible. For this purpose we analysed the MM5
output for the whole PBL levels. The chosen PBL parameterizations are: 1)
Gayno-Seaman; 2) Medium-Range Forecast; 3) Mellor-Yamada scheme as used in
the ETA model; and 4) Blackadar.
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