In January 2007 a control car was lifted of the tracks in a narrow valley of the Alpstein mountain range, which is indicative for extreme local wind maxima surpassing 50 m/s. These so-called Laseyer winds occur once or several times in most winters. The wind gusts come up in quasi-oscillatory manner for several hours. So far, no theory is able to explain the Laseyer winds. In this project, the origin of the strong wind gusts is investigated by means of real-case and idealized numerical simulations.
In a first step, high resolution simulations of the atmospheric flow conditions around the Alpstein mountain range are conducted. These simulations are performed with the COSMO-2 weather prediction model. The COSMO-2 model is an implementation of the limited-area model developed within the framework of the Consortium for Small-Scale Modelling (COSMO, http://cosmo-model.cscs.ch/).
In a second phase, the output of the COSMO-2 model is then coupled to the Advanced Regional Prediction System model (ARPS, http://www.caps.ou.edu/ARPS/ ) run in large eddy simulation mode with a grid spacing of 50-100m. The ARPS model run is applied to the valley and its immediate surrounding
On a second track, measurements of local weather stations are analyzed and compared to the model results, thus assessing the quality of the numerical simulation of the event. Additionally, several years of measurements are objectively analyzed for similar Laseyer winds and a simple climatology is established.
Lukas Egloff: lukas.egloff [at] ethz.ch
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