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Factors Affecting the Velocity and Direction of Wind

 

Wind movement UPSC

  • Horizontal movement of air is called wind.
  • Vertical movement of air is called current.
  • The wind blows from high pressure to low pressure.
  • Wind movement is influenced by a variety of factors like friction, rotation of earth etc.
  • The wind movement in near the earth surface is respond to the combined effect of three forces – the pressure gradient force, the frictional force and the Coriolis force. In addition, the gravitational force acts downward.

 

Pressure Gradient Force

  • The differences in atmospheric pressure produces pressure gradient force.
  • The rate of change of pressure with respect to distance is the pressure gradient.
  • The pressure gradient is strong where the isobars are close to each other and is weak where the isobars are apart.
  • So, in a closely spaced gradient, steep pressure change is found due to which there is a strong wind speed.

 

Factors Affecting the Velocity and Direction of Wind_30.1

 

Coriolis force

  • The rotation of the earth about its axis affects the direction of the wind.
  • This rotation produces a force called a Coriolis force, which is named after a French physicist.
  • This force deflects the wind to the right direction in the northern hemisphere and to the left in the southern hemisphere, thus following Farrell’s law.
  • Also, the deflection is more when the wind velocity is high.
  • The Coriolis force is directly proportional to the angle of latitude.
  • It is maximum at the poles and is absent at the equator.
  • The Coriolis force acts perpendicular to the pressure gradient force.

 

Frictional force

  • Friction is caused due to the irregularities of the earth’s surface, which offers resistance to the wind movement.
  • Frictional force affects the speed of the wind.
  • It is greatest at the surface and its influence generally extends upto an elevation of 1 – 3 km.
  • Over the sea surface the friction is minimal.

 

Factors Affecting the Velocity and Direction of Wind_40.1

 

Why tropical cyclones are not formed near the equator?

  • As we know that the Coriolis force acts perpendicular to the pressure gradient force.
  • The pressure gradient force is perpendicular to an isobar.
  • So, higher the pressure gradient force, the more is the velocity of the wind and the larger is the deflection in the direction of wind.
  • Due to the two forces operating perpendicular to each other, in the low-pressure areas, the wind blows around it.
  • At the equator, the Coriolis force is zero (discussed above) and the wind blows perpendicular to the isobars.
  • The low pressure gets filled instead of getting intensified.
  • That is the reason why tropical cyclones are not formed near the equator.

 

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