Winds Blowing Across Hilly Terrain
| On windy occasions such as the approach of a tropical cyclone, air streams of high wind speed may emerge from mountain gaps. Lying between these high-speed air streams are air streams of lower wind speed. Aircraft traversing through alternating high-speed and low-speed air streams may encounter headwind losses and gains at different locations along the approach and departure corridors.
In particular, if an aircraft flies from a low-speed air stream to a high-speed air stream, it may experience a large headwind gain leading to a lift of the aircraft. If the aircraft moves from a high-speed air stream to a low-speed air stream, it may experience a large headwind loss resulting in a sinking motion. |
 Windshear induced by winds blowing across hilly terrain  Wind pattern captured by the Terminal Doppler
Weather Radar during the passage of Severe Tropical Storm Hagupit in September 2002 |