FAA Aircraft Dispatcher (ADX)MeteorologyMedium
A dispatcher is briefing a flight crew on surface wind flow around pressure systems in the Northern Hemisphere. How does surface wind circulate around a low-pressure system compared to a high-pressure system, accounting for friction?
- ACounterclockwise and outward around a low; clockwise and inward around a high
- BCounterclockwise and inward around a low; clockwise and outward around a high
- CClockwise and inward around a low; counterclockwise and outward around a high
- DClockwise and outward around a low; counterclockwise and inward around a high
Show answer & explanationAnswer & explanation
Correct answer: B. Counterclockwise and inward around a low; clockwise and outward around a high
In the Northern Hemisphere, the Coriolis force deflects wind to the right, causing surface winds to flow counterclockwise and spiral inward toward a low-pressure center, while flowing clockwise and spiraling outward away from a high-pressure center due to surface friction reducing the balance between pressure gradient and Coriolis forces.
Why the other options are wrong
- A. The rotation directions here are reversed relative to actual Northern Hemisphere circulation.
- C. This reverses the correct rotational directions for low and high pressure systems.
- D. This describes Southern Hemisphere rotation combined with incorrect flow directions.
Surface Wind Circulation Around Pressure Systems
In the Northern Hemisphere, friction causes surface winds to spiral counterclockwise and inward around lows, and clockwise and outward around highs.
- Coriolis force deflects wind to the right in the Northern Hemisphere
- Friction disrupts geostrophic balance, causing winds to cross isobars toward low pressure
- Aloft (above friction layer), wind flows parallel to isobars (geostrophic wind)
Memory trick: 'Low sucks in, spins left; High blows out, spins right' (Northern Hemisphere).