Texas A&M University (TAMU) GEOG 203 Planet Earth Exam 1 Practice Test

Friction between the air and the Earth's surface acts as a drag on the moving air. This drag slows the wind near the ground, so it doesn’t reach the speeds it would have if only the pressure gradient force were acting. In the upper atmosphere, winds tend to flow parallel to the isobars because the pressure gradient force is balanced by the Coriolis effect. Near the surface, friction weakens that balance, causing winds to cross isobars and slow down. So the primary effect of friction is to reduce wind speed through drag, making the surface wind slower than it would be otherwise. Friction does not speed up the wind, and while it does influence vertical mixing, its most noticeable impact on horizontal wind is this slowing effect.