FAA Aircraft Dispatcher (ADX)MeteorologyMedium
A dispatcher reviewing overnight surface observations at an airport near elevated terrain notes that after sunset, cold dense air steadily drains down the mountain slopes into the valley, increasing surface wind speed near the airport. This phenomenon is best classified as a:
- AKatabatic wind
- BFoehn wind
- CGeostrophic wind
- DAgeostrophic wind
Show answer & explanationAnswer & explanation
Correct answer: A. Katabatic wind
A katabatic wind is a gravity-driven flow of dense, cold air downslope, typically occurring at night as radiational cooling chills air near elevated terrain, causing it to sink and accelerate into valleys.
Why the other options are wrong
- B. A foehn wind is a warm, dry downslope wind on the leeward side of mountains, unrelated to nighttime cooling.
- C. Geostrophic wind results from pressure gradient and Coriolis balance aloft, not local terrain drainage.
- D. Ageostrophic wind refers to any wind deviating from geostrophic balance, not specifically drainage flow.
Katabatic Wind
A downslope wind caused by cold, dense air draining from higher terrain into valleys, most common on clear nights with light gradient winds.
- Driven by radiational cooling and gravity
- Occurs mainly at night in mountain/valley terrain
- Opposite of foehn wind, which is warm and adiabatically heated
Memory trick: Katabatic = 'cold air cascades' downhill after dark.