factors affecting wind speed
Due to atmospheric pressure, the air is set in motion. This is called Wind. This wind flows from a high-pressure area to low pressure area. Apart from the air pressure, the rotation of the earth also influences the rotation of the earth.
The force exerted by the rotation of the earth is called Coriolis force or effect. Altogether, the horizontal winds nearer to the surface of the earth are affected by the three forces combined such as the pressure gradient force, frictional forces, and the Coriolis force.
Also, the gravitational force acts downward.
Pressure Gradient Force
The force in the atmosphere is produced by differences in atmospheric pressure. The rate of change of pressure corresponding to the distance is called the Pressure Gradient. The Pressure gradient force causes the winds to blow.
The pressure gradient is strong when the Isobars are close and weak when the Isobars are far apart. That is, the wind blows from higher pressure to lower pressure, and also when there is a greater pressure difference, the greater is the wind speed.
The pressure gradient is perpendicular to an isobar. Also, the higher the pressure gradient, the more is the speed of the wind and also the higher is deflection in the direction of the wind. The velocity of the wind is directly proportional to the pressure gradient. That as the pressure increases a.k.a pressure gradient increases by which the speed of the wind also increases at the particular location.
The Pressure Gradient force is the one that triggers the initial movement of air.
Causes of Pressure Gradient Force
The difference in air pressure and pressure gradient is caused because of the unequal heating of the earth’s surface and the concentration of the incoming solar radiation at the equator. Also due to the energy surplus at low latitudes. Ex: Air is warm at the equator and Air is cold at the poles.
Frictional Force
The air is a fluid, the air molecules rub across the surface of the earth and the object over it such as hills, trees, etc. Also, the air above the surface faces little friction
Frictional forces influence the speed of the wind. The frictional force is greatest at the surface and it influences, generally to an altitude of 1 to 3 Km. The frictional force is minimal at the surface of the sea. Simply, the friction is greatest near the earth’s surface and it rapidly decreases with altitude or height.
The layer where the air is highly affected by the frictional force and the surface is called the boundary layer. The frictional force has two effects on the wind, first it opposes the direction of motion by acting opposite to the airflow, and second, it affects the speed of the wind.
The effect of friction is different on different terrains. On hilly terrains, winds are deflected by 30° or more. On the other hand on flat landforms, it is negligible.
Coriolis Force
The direction of wind is affected by the rotation of the earth about the axis. This force due to the rotation of the earth is known as the Coriolis force.
As per the French Physicist Gustave-Gaspard Coriolis, who not that the Force due to the rotation of the earth, deflects the wind to the right direction in the Northern Hemisphere and to the left in the Southern Hemisphere.
Also observed, is that the deflection is more when the velocity of the wind is high. The Coriolis forces are directly proportional to the angle of latitude and are maximum at the poles and are absent at the equator.
This force acts perpendicular to the pressure gradient force. The wind blows in the low-pressure area.
In the equator, the Coriolis force is zero, and the wind blows perpendicular to the isobars. As result, the low pressure gets filled rather than getting intensified. Due to this tropical cyclones were not formed near the equator.
Pressure
The velocity and direction of the wind are the final output of the wind-generating forces. Above 2 to 3 km above the surface of the earth, the wind is free from the frictional effect of the surface.
In such heights, winds are affected only by the Coriolis forces and pressure gradient. If Isobars are straight and if there is no friction, the pressure gradient force is balanced by the Coriolis force and wind arises out of it blowing parallel to the isobar. This wind is called Geostrophic Wind.
The wind circulation around a low is called Cyclonic Circulation and around the high is called Anti Cyclonic Circulation. The Winds direction around such a system change as per their location in Southern Hemisphere or Northern Hemisphere.
| Pressure System | Pressure condition at the Centre | Northern Hemisphere | Southern Hemisphere |
| Cyclone | Low | Anticlockwise | Clockwise |
| Anticyclone | High | Clockwise | Anticlockwise |
The wind circulation at the earth’s surface around low and high, on different occasions, is closely related to the higher-level wind circulations.
Over the low-pressure area, the air converges and rises. In high-pressure areas, the air will subside from above and diverge at the surface. Apart from convergence, some eddies, convection currents, orographic uplift, and uplift along the fronts cause the air to rise. This is the basic need for the formation of clouds and precipitation.
Conclusion
In these notes, we have discussed the topic ‘Factors affecting speed and direction of the wind‘ in Physical geography and the areas covered are factors and outcomes due to the speed and direction of winds. This note is extremely useful for Upsc, Tnpsc, and other government service exams.
References
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