Flow Past a Steep Mountain: Testing Hypotheses by Combining Numerical Simulations with Observations

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The flow in the lee of a steep mountain is characterized by highly complex vortical structures. Previous research based on idealized numerical simulations has suggested that the shape of these lee vortices sensitively depends on the vertical shear of the ambient wind; on the other hand, the strength of the ambient wind is of minor importance. Here it is proposed to test these hypotheses though a combination of numerical simulations and observations. A one-month long measurement campaign will, for the first time, probe the wind field in the neighborhood of the Matterhorn using modern wind LiDAR technology in combination with radiosonde ascents and a small unmanned meteorological aircraft. In addition, extensive large eddy simulations of flow past a mountain will be performed and analzyed. The use of realistic Matterhorn orography allows one to develop the best measurements strategies for the campaign, and later to put the measurements into the context of earlier results. In addition, the simulations will be used to study the transient behavior of the wind field in the lee of a steep mountain, both with idealized and realistic orography. An important aspect thereby is the visualization of the lee vortices, which facilitates the testing of the above mentioned hypotheses.