Definition

Mountain Waves is defined as oscillations to the lee side (downwind) of high ground resulting from the disturbance in the horizontal air flow caused by the high ground.

Description

The wavelength and amplitude of the oscillations depends on many factors including the height of the high ground relative to surrounding terrain, the wind speed and the instability of the atmosphere.

Formation of Mountain Waves can occur in the following conditions:

• Wind direction within 30 degrees of the perpendicular to the ridge of high ground and no change in direction over a significant height band.
• Wind speeds at the crest of the ridge in excess of 15 kts, increasing with height.
• A temperature inversion just above the hill or mountain barrier.