Pressure gradient force is responsible for triggering the initial movement of air, which in turn leads to the development of wind. It is directed from higher to lower pressure at right angles to the equal pressure surfaces, isobars . The closely spaced isobars in a weather chart indicate steep pressure gradients, strong forces, and high winds, while widely spaced isobars indicate gentle pressure gradients, weak forces, and light winds. The centripetal force is responsible for a change in direction of the wind and not a change in speed. It deflects the wind to the right of its initial direction in the Northern Hemisphere and to the left in the Southern Hemisphere.
Coriolis force is zero at the equator and increases with latitude to a maximum at the poles.
The deflection also increases with increasing wind speed. The coriolis effect is important only in large-scale circulation systems. The friction of fluid flow, known as viscosity , is of two types, molecular and eddy. The molecular viscosity arises from the random motion of molecules composing a liquid or gas. The eddy viscosity arises from the random motion of eddies within a fluid such as air or water.