The pressure gradient force is directed inward at all points around the low. The coriolis force is directed to the right of the direction of motion. For this case of counterclockwise flow, the Coriolis force will always be directed outward, away from the low pressure center. Explain how the friction force works. Friction results from collisions between moving air molecules and a stationary surface, and also from collisions between individual molecules near the surface of the earth where the density of air moilecules is greatest.
Friction slows surface winds.
Slower moving air is not deflected as much by the Coriolis force. As a result, the pressure gradient force can become slightly larger than the Coriolis force, and air will flow across isobars from high pressure to low pressure. This cross-isobaric flow generates convergence and divergence of surface air which is related to vertical air motions. Explain how a dust devil may form on a hot, clear day in Tucson. On a hot day sirface heating will cause air to rise through convection.