Meteorology · Synoptic Charts — Surface Friction
Compared with the geostrophic wind aloft, how does surface friction over the open sea modify the wind?
- AIt reverses the wind direction
- BIt speeds the wind and turns it parallel to the coast
- CIt has no effect over water
- DIt slows the wind and backs it so it crosses the isobars at roughly 10°–20° toward lower pressure✓ Correct
Explanation
Friction reduces wind speed and weakens the Coriolis deflection, so the surface wind backs (turns counterclockwise in the NH) and blows across the isobars toward low pressure — about 10°–20° over water versus 25°–35° over rougher land.
Authority: Bowditch (Pub. No. 9), surface wind and friction; WMO
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