Investigation of observed and modelled nocturnal wind and temperature oscillations in an Alpine valley

At three sites located slightly above the valley bottom of the Inn Valley, a major Alpine valley, measuremens have been carried out from 20 November 2005 to 10 March 2006 during winter conditions with snow cover. All site were equipped with sensitive propellor anemometers and temperature measurements at two levels on a mast. In addition, at one of the sites, ultrasonic anemometer was operated. Several events of nocturnal wind and temperature oscillations were found at all three stations. During these events, temperature decreases by more 3 K within 10 minutes while wind direction changes from down-slope to a direction from the lowest part of the valley towards the station with increasing wind speed. First investigations have shown that oscillations are accompanied by sign changes of the sensible heat flux where the flux is away from the surface in the cold phases.

A MM5 simulation with a resolution of 270 m in the innermost nest has been carried out with recording of the output in 5 minute intervals. First inspection of the model output shows oscillatory features also in the model.