qA force of opposition
which slows air in motion.
qInitiated at the
surface and extend, decreasingly, aloft.
qImportant for air
within 1.5 km (1 mi) of the surface, the planetary boundary layer.
qBecause friction
reduces wind speed it also reduces Coriolis
deflection.
qFriction above 1.5 km
is negligible.
qAbove 1.5 km = the free atmosphere.