FAA Sport Pilot Airplane (SPA)WeatherHard
On a clear, calm night in mountainous terrain, a pilot is briefed that cool, dense air is draining down the mountain slopes into the valley floor after sunset. What is this local wind phenomenon called?
- AAn anabatic (valley) wind
- BA katabatic (mountain/drainage) wind
- CA land breeze
- DA chinook wind
Show answer & explanationAnswer & explanation
Correct answer: B. A katabatic (mountain/drainage) wind
A katabatic wind, also called a mountain or drainage wind, occurs at night when air near mountain slopes cools by radiation, becomes denser, and flows downhill into valleys; the opposite daytime upslope flow is called an anabatic or valley wind.
Why the other options are wrong
- A. Anabatic (valley) winds flow upslope during the day due to solar heating, the opposite of this scenario.
- C. A land breeze is a coastal thermal circulation, not a mountain drainage wind.
- D. A chinook is a warm, dry downslope wind on the lee side of a range, unrelated to nighttime radiational cooling.
Katabatic (Mountain) Wind
A katabatic wind is a nighttime downslope flow of cool, dense air draining from higher mountain terrain into valleys, driven by radiational cooling of the slopes after sunset.
- Occurs at night under clear, calm conditions
- Cool dense air sinks and flows downhill
- Opposite of daytime anabatic (valley) upslope wind
Memory trick: Katabatic = 'cat creeping downhill' after dark.