Definition
The flow that results when the pressure gradient force exactly balances the Coriolis force, giving wind parallel to straight isobars. It is what a geostrophic scale on a synoptic chart measures from isobar spacing and latitude. Real surface wind over the open sea is typically about two thirds of the geostrophic value and backed 10 to 20 degrees towards low pressure, with a greater reduction and larger backing over land.
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