causes of inter annual variation

Movement of wind from one area to another depends on pressure differences.

• A weakening in pressure differences between two areas reduces the flow of wind between the two areas.

• Major sources of atmospheric moisture are oceans and rain forests in equatorial regions.

• Weakening of pressure differences between land and oceans can affect movement of moisture from oceans to the land.

• Atmospheric pressure over oceans greatly depend on temperature of the water in the oceans (Sea Surface Temperatures).

• Warming of the oceans results in warming of the air above and therefore reducing air pressure.

• Cooling has the opposite effects.