Backing is a term meaning "to turn in a counterclockwise direction". On a certain day in Santiago, Chile, the PGF (pressure gradient force) remains constant in size and direction in the lowest 1 km of the atmosphere (i.e. from the ground to 1 km above the ground).
Explain why the wind direction in the lowest 1 km of the atmosphere backs with increasing height on that day. (HINT: Consider the force balances at the surface and at 1 km)