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Pressure and Wind

Forces affecting the Velocity and Direction of Wind, Convergence and Divergence of winds etc.

  • The wind is air in motion that blows from high pressure to low
  • Forces impacting Wind Velocity and Direction: Wind is air in motion that blows from high to low
  • At the surface, the wind encounters friction
  • The wind is also affected by the earth’s rotation. The Coriolis Force is the force exerted by the rotation of our sphere
  • Horizontal winds at the earth’s surface are influenced by three forces: Pressure Gradient Force, Frictional Force, and Coriolis Force
  • Furthermore, gravitational force is directed downward

Pressure Gradient Force

  • A force is created by variances in air pressure
  • The pressure gradient is the speed of conversion of pressure concerning distance
  • When the isobars are nearer, the pressure gradient is large; when separated, the pressure gradient is mild

Frictional Force

  • It has an impact on wind speed
  • Its influence is greatest at the surface and often extends up to a height of 1-3 km
  • The friction on the sea surface is negligible

Coriolis Force

  • The course of the wind is affected by the earth’s rotation around its axis. The Coriolis Force is named after the French physicist who first described it in 1844
  • The Northern Hemisphere deflects the wind to the right, and the high surface deflects the wind to the left in the Southern Hemisphere. When the wind speed is high, the deflection is greater
  • The angle of latitude is directly proportional to the Coriolis Force. It reaches its highest point in the poles and is completely absent near the equator
  • The pressure gradient force acts perpendicular to Coriolis Force. An isobar’s pressure gradient force is perpendicular
  • The bigger the pressure gradient force, the higher the wind velocity and the greater the deviation in wind direction
  • Because those two forces are perpendicular to one other, the wind whirls around it in low-pressure areas
  • On the equator, the temperature is zero, and the wind runs perpendicular to isobars. Instead of intensifying, the low pressure is filled. Tropical cyclones do not form near the equator for this reason

Pressure and Wind

  • The total outcome of the wind generating forces is the wind’s velocity and direction
  • The winds in the higher atmosphere (above 2-3 km) are primarily governed by pressure gradient force plus Coriolis Force
  • When isobars are accurate and there is no resistance, the Coriolis Force balances the pressure gradient force, including the wind flows parallel to isobar. The geostrophic wind is the name given to this type of wind

Vertical Variation of Pressure

  • The pressure drops significantly with falling height at a lower atmosphere. 

  • Every 10m rise in elevation causes a loss of around 1mbar. It doesn’t always go down at the same pace.

  • The force of the vertical pressure gradient is substantially higher than the horizontal pressure gradient. 

  • It often counterbalances when it encounters a gravitational pull that is nearly equal yet opposite. As a result, there aren’t any strong rising breezes. 

Horizontal Distribution of Pressure:

  • In terms of wind direction and velocity, the small changes in pressure are significant.

  • Drawing isobars at fixed levels are used to investigate the horizontal distribution of pressure. Isobars are lines that connect points of equal pressure.

  • One or more isobars surround a low-pressure system, with the lowest pressure right in the centre.

  • One or more isobars surround a high-pressure system, with the highest pressure right in the centre.

A cyclonic circulation is the wind circulation in a low-pressure area. Anticyclonic circulation occurs when a high pressure exists. The direction is different.

Cyclonic and Anticyclonic Circulation

  • In many circumstances, the low and high wind circulations near the earth’s surface are strictly related to wind circulation at a higher altitude.

  • The air will concentrate and float over low-pressure areas in general.

  • The air will subside from above and diverge at the surface over a high-pressure area.

  • Apart from convergence, convection currents, eddies, orographic uplift, and uplift with fronts cause air to rise, and high surfaces are necessary for cloud and precipitation development.

  • The wind circulation at the earth’s surface around low and high on many occasions is closely related to the wind circulation at higher levels.

  • Generally, over a low pressure area the air will converge and rise and over a high pressure area the air will subside from above and diverge at the surface, which is referred to as convergence and divergence of winds.

Forces affecting velocity and direction of wind

Rotation of the earth affects the wind movement

  • Force exerted by the rotation of the earth is known as the coriolis force

  • Horizontal winds near the earth surface respond to the combined effect of forces, i.e the pressure gradient force, the frictional force and the coriolis force.

    • Pressure Gradient Force – The rate of change of pressure with respect to distance is the pressure gradient.

    • Frictional Force – It affects the speed of the wind and is greatest at the surface.

    • Coriolis Force – The rotation of the earth about its axis affects the direction of the wind is called the coriolis force.

  • Velocity and direction of the wind are the net result of the wind generating forces.

  • The pattern of planetary winds mainly depends on latitudinal variation of atmospheric heating, emergence of pressure belts, the migration of belts following the apparent path of the sun, the distribution of continents and oceans and the rotation of earth.

  • The pattern of the movement of the planetary winds is called the general circulation of the atmosphere.

 

Thunderstorms and Tornadoes

Thunderstorms are caused by intense convection on moist hot days. A thunderstorm is a well-grown cumulonimbus cloud producing thunder and lightning. From severe thunderstorms sometimes spiralling wind descends like a trunk of an elephant with great force, with very low pressure at the centre, causing massive destruction on its way. Such a phenomenon is called a tornado. 

The violent storms are the manifestation of the atmosphere’s adjustments to varying energy distribution. The potential and heat energies are converted into kinetic energy in these storms and the restless atmosphere again returns to its stable state

 

Conclusion

Atmospheric pressure is measured with the help of an instrument called mercury barometer. The general circulation of the atmosphere sets in motion the ocean water circulation which ultimately influences the earth’s climate and also affects the oceans.