It acts only on air that is flowing around centers of circulation. Centripetal acceleration is also another force that can influence the direction of wind. This force produces a circular pattern of flow around centers of high and low pressure. Centripetal acceleration is much more important for circulations smaller than the mid-latitude cyclone . The last force that can influence moving air is frictional deceleration .
Friction can exert an influence on wind only after the air is in motion.
Frictional effects are limited to the lower one kilometer above the Earth's surface. Winds of this type are usually called geostrophic winds . A geostrophic wind flows parallel to the isobars. This deflection continues until the pressure gradient force and Coriolis force are opposite and in balance with each other. Figure 5n-7 models air flow in the Northern Hemisphere.