CAAP Private Pilot License (PPL) Meteorology Practice Test

The wind at 5,000 feet AGL is south westernly while the surface wind is southerly. This difference is primarily due to

Pressure gradient Coriolis at the surface Temperature lapse rate Friction

Correct Answer:

Friction

Explanation:

Friction near the surface slows the air, which weakens the Coriolis effect and allows the wind to cross the isobars toward lower pressure. In the upper atmosphere, the Coriolis force more effectively deflects the wind so it tends to flow more parallel to the isobars (geostrophic balance). When you bring friction into the picture at low levels, the balance shifts, and the wind veers across the pressure gradient toward lower pressure. That cross-isobar flow changes the direction from aloft to the surface, producing the surface wind that is more southerly while the higher wind is southwest. Temperature lapse rate and the mere pressure gradient aren’t the primary drivers of this directional change; friction is.

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