Horizontal pressure differentials result in the flow of air that we call wind
(Fig. 1.12). Winds coming from the north in the Northern hemisphere and from the
south in the Southern hemisphere are deflected towards the west as they migrate from
a region where the Earth is rotating slowly (at the poles) to where it is rotating most
rapidly (at the equator). Winds travel nearly parallel to the isobars, with low pressure
to their left in the Northern hemisphere and to the right in the Southern hemisphere.
At the surface, where wind speeds are lower, the winds tend to travel perpendicular to
the isobars from high to low pressure. This differential motion results in a spiral outward
flow of air clockwise in the Northern hemisphere around a high and an inward
counterclockwise flow around a low.