FAA Sport Pilot Airplane (SPA)WeatherMedium
A pilot studying a surface analysis chart notes a low-pressure system near the route of flight. In the Northern Hemisphere, how does surface wind circulate around this system?
- AClockwise and inward toward the center
- BClockwise and outward from the center
- CCounterclockwise and outward from the center
- DCounterclockwise and inward toward the center
Show answer & explanationAnswer & explanation
Correct answer: D. Counterclockwise and inward toward the center
In the Northern Hemisphere, surface winds flow counterclockwise and inward around a low-pressure system due to the pressure gradient force combined with the Coriolis force and surface friction. Around a high, the flow is clockwise and outward.
Why the other options are wrong
- A. Low-pressure flow is counterclockwise, not clockwise.
- B. This describes flow around a high-pressure system, not a low.
- C. Outward flow describes a high, and the rotation described here is also incorrect for a low.
Pressure System Circulation (N. Hemisphere)
Surface wind circulates counterclockwise and inward around lows, and clockwise and outward around highs in the Northern Hemisphere.
- Low pressure: counterclockwise, converging (inward)
- High pressure: clockwise, diverging (outward)
- Reversed in the Southern Hemisphere
- Convergence in lows promotes lifting and clouds/precipitation
Memory trick: Low sucks air in Counterclockwise like a drain; High blows out Clockwise like a fan.