The weight of the Earth's atmosphere exerts pressure on the surface of the Earth. This pressure varies from place-to-place and from time-to-time due to surface irregularities, uneven heating of the atmosphere by the sun, and the Earth's rotation. Differences in pressure from place-to-place cause winds to try to flow from high pressure to low pressure regions to even out the differences, but the Earth's rotation and wind friction with the surface act to slow or divert the winds. This animation shows the surface wind speeds for the whole globe from September 1, 2004, through September 5, 2004, during the period of Hurricane Frances in the western Atlantic Ocean and Typhoon Songda in the western Pacific Ocean. The highest, smoothest winds occur over the oceans where there are no surface irregularities to break up the flow, while flows over land tend to be irregular and highly variable. The highest winds occur in Hurricane Frances and Typhoon Songda, but note that the hurricane's wind speeds reduce dramatically when crossing Florida.
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