Abstract
Stably stratified airflows over a hill or mountain are studied by a wind tunnel and also by a theoretical model with special forcus on the upstream stagnant zone. The wind tunnel experiment shows that a stagnant zone is formed upstream of an obstacle when the Froude number is less than some critical value. The critical Froude number is found to vary with the obstacle height. In the stagnant zone, the airflow is negligible or reverse and the thickness of the zone decreases gradually with the distance from the obstacle.
