FAA Sport Pilot Airplane (SPA)WeatherHard
A pilot studying atmospheric circulation learns that a moving air parcel in the Northern Hemisphere is deflected to the right of its path of motion, ultimately causing wind aloft to flow nearly parallel to the isobars rather than directly from high to low pressure. Which force causes this deflection?
- ACoriolis force
- BCentrifugal force
- CFrictional force
- DPressure gradient force
Show answer & explanationAnswer & explanation
Correct answer: A. Coriolis force
The Coriolis force results from the Earth's rotation and deflects moving air to the right in the Northern Hemisphere (left in the Southern Hemisphere). Above the friction layer, this deflection balances the pressure gradient force, causing wind to flow parallel to isobars as geostrophic wind.
Why the other options are wrong
- B. Centrifugal force affects wind curving around pressure centers but is not the primary deflecting force described.
- C. Frictional force acts near the surface, causing wind to cross isobars at an angle, not aloft where flow is parallel.
- D. Pressure gradient force initiates air movement from high to low pressure but does not cause the rightward deflection.
Coriolis Force
An apparent force caused by the Earth's rotation that deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, increasing with wind speed and latitude.
- Deflects wind right in N. Hemisphere, left in S. Hemisphere
- Zero at the equator, maximum at the poles
- Balances pressure gradient force to create geostrophic wind aloft
- Combined with friction near the surface, causes wind to cross isobars toward low pressure
Memory trick: Coriolis Curves wind to the right, like a spinning merry-go-round.