Weather Systems

Without the Coriolis force, the weather on earth would be completely different from the weather we know. When a low pressure system is formed, air would rapidly flow from high pressure regions to the low pressure region if the earth did not rotate. In fact pressure waves travel at the speed of sound so pressure differences would be damped out in hours at the most. With the Coriolis force, the air will be deflected to the right in the northern hemisphere as shown in the figure below.

The air circulates around a low pressure system in a counter-clockwise direction with the Coriolis force pushing the air outward while the force from the pressure difference pushes the air inward toward the low pressure. The two forces balance each other (automatically) and semi-stable low (and high) pressure systems last for weeks or even months, moving across the earth while the air swirls around them. In stable weather systems, the wind actually blows along isobars, rather then perpendicular to them. The figure below shows a large low pressure system over Iceland. It is clearly swirling in the counter-clockwise direction.
Huricanes are an extreme example of a low pressure system. They are produced over warm water (but not near the equator).

High pressure systems, like ones causing Santa Ana conditions in San Diego have air swirling clockwise in the northern hemisphere.

Tornados are a different phenomonon due to turbulence and remanent angular momentum.

Jim Branson 2012-10-21