Mesoscale Alpine Programme (MAP)

TEA CO₂ Doppler Lidar Observations
in Mountainous Terrain during MAP

TEA CO₂ Doppler Lidar at the MAP field site in Austria's Wipptal Valley

Launching a radio sonde near the TEA CO₂ Doppler Lidar at the MAP field site.

The Mesoscale Alpine Programme (MAP) provided an opportunity to participate in an international collaboration focusing on the effects of complex 3-D topography on wind, precipitation, and flooding. In response, we deployed TEA CO₂, our most powerful ground-based Doppler lidar, near Innsbruck, Austria, October 1 through November 15, 1999. One of the principle objectives of the program was the investigation of "gap flows" - winds that blow through gaps between mountain ranges, mountain passes, and other topographic low points. To address this objective, the Doppler lidar was strategically positioned in the Wipptal Valley just north of the Brenner Pass for measurements of the terrain-induced flow structures.

By measuring the change in frequency of laser light reflected from windborne aerosol particles, the NOAA lidar can estimate the wind speed to distances of more than 15 miles. During MAP, the lidar was used to map out the flow along, across, and above the valley, providing information on the path taken by the strongest winds as they surge down the Wipptal. These observations, in conjunction with simultaneous aircraft measurements from above the mountaintops, will be analyzed to evaluate and improve numerical models that characterize the onset, severity, and structure of winds flowing through mountain gaps. Lidar measurements obtained during an October foehn event at MAP showed that wind speeds were actually higher on the valley floor then at mountaintop levels. The depth and strength of the strongest winds increased during the course of the foehn event, which lasted for approximately 36 hours.

Because of the massive commitment to measurement infrastructure from the alpine European countries, the observations network available to test and improve the models of downslope winds during MAP far exceeded that from prior experiments. It was actually much cheaper to deploy U. S. observational tools such as the lidar to Europe than to duplicate the measurement network for a North American based study. Results from MAP will eventually lead to better forecasts of downslope wind events. The strong surface winds that occur during severe episodes often pose a severe hazard to shipping and fishing in the straits of the Pacific Northwest and Alaska, affect the transport of polluted air from the Los Angeles basin, and cause severe damage to structures in the lee of the Rocky Mountains.

References:

Banta R.M., L.S. Darby, R.K. Newsom, R.M. Hardesty, J.N. Howell. Atmospheric gravity waves, low-level jets, and mountain gap flows measured by ETL's Doppler lidars during October 1999. 20th International Laser Radar Conference, Vichy, France, 10-14 July (2000).

Related Topics

TEA CO₂ lidar
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