Forces Controlling Winds

Pressure Gradient and Winds

  • There is a close relationship between the pressure and the wind speed.
  • The greater the difference in air pressure between the two points, the steeper is the pressure gradient and greater is the speed of the wind.
  • The gentler the pressure gradient slower is the speed of the wind. (see fig).

Winds

The Coriolis Effect and Wind

  • Winds do not cross the isobars at right angles as the pressure gradient directs them.
  • They get deflected from their original paths.
  • One of the most potent influences on wind direction is the deflection caused by the earth’s rotation on its axis.
  • Demonstrated by Gaspaved de Coriolis in 1844 and known as the Coriolis effect or coriolis force.
  • Coriolis force tend to deflect the winds from their original direction.
  • In northern hemisphere winds are deflected towards their right, and in the southern hemisphere towards their left (see fig.) This is known as Ferrel’s law.
  • The Coriolis force is absent along the equator but increases progressively towards the poles.

Winds

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Types of Winds

For ages man has observed that in some areas of the earth the winds blow predominantly from one direction throughout the year; in other areas the wind direction changes with the season and in still others the winds are so variable that no pattern is discernible. Despite these difference, the winds are generalized under three categories.

  • (a) Planetary winds or permanent winds
  • (b) Periodic winds or Seasonal winds
  • (c) Local winds