Winds

Winds

Wind - Air in motion is known as wind.

Reason of Motion of air (wind) -

1.   Pressure Gradient force

Difference in atmospheric pressure 🠊 Causes/produces a force which pulls the air from high pressure to low pressure.

2.   Frictional force

It opposes the motion. It is greater on land than that on ocean.

3.   Coriolis force

It is the force exerted due to the rotation of the Earth. It deflects object (air) towards right in Northern hemisphere and towards left in Southern hemisphere.

Wind - Wind is air in motion. The causes of the motion of air are -

1. Pressure gradient force - The rate of change of pressure with respect to distance is called pressure gradient. The pressure differential in the atmosphere causes the movement of air from high pressure to low pressure. The force causing this movement is known as Pressure gradient force. Closer the isobars, stronger the pressure gradient force and stronger the wind blows.
2. Frictional force - Any moving object near to the land surface experiences frictional force in the direction opposite to that of its movement. It is maximum along the land and near to the surface than over oceans and above higher altitude.
3. Coriolis force - It is an imaginary force which is being felt by any object which is on a body which is on motion (rotational motion). The rotation of the Earth causes Coriolis force. It results in the deflection of body towards right in Northern hemisphere and towards left in the Southern hemisphere.

Coriolis force depends on 

• Latitude (Sine function, i.e., Sin ɸ) - It is zero at Equator and Maximum at Poles.
• Speed of rotation of the Earth - More the speed, stronger will be the Coriolis force.
• Speed of object - Greater the speed of the object, stronger Coriolis force will be experienced.

Coriolis force (effect on wind)

• Coriolis force is a fictional force produced due to the rotation of the Earth.
• It causing any moving object to deflect towards the right in Northern hemisphere and towards left in the Southern hemisphere.
• The degree of Coriolis force depends on - Wind Velocity (higher the wind speed, more the Coriolis force), Latitude (It is maximum along the poles and zero at the equator) and Speed of rotation of the Earth (Greater the speed, more the Coriolis force and more the deflection of wind).

Types of winds -

1. Geostrophic Winds
2. Planetary winds
3. Seasonal winds
4. Local winds
5. Land and Sea breeze
6. Mountain and Valley breeze

Geostrophic wind -

Assume, Frictional force = 0,

At equator - Coriolis force is also zero, Therefore direction of wind is ↑.

At 30° N - Coriolis force and Pressure gradient force both are acting, Therefore direction of wind is ↗.

At 60° N deflection is more towards the right.

At poles - Coriolis force is maximum and thus overshadowing the effect of Pressure gradient force and the wind blows in the direction of Coriolis force (→).

• Inspite of pressure difference (pressure gradient force), the wind will move perpendicular to the direction of pressure gradient force due to very high coriolis force. This system of wind is known as Geostrophic wind.
• In this system, winds move parallel to the pressure belts.
• Pressure difference will never settled as wind moves perpendicular to the pressure gradient force. So, wind moves continuously.

Geostrophic winds -

The Coriolis force deflects the winds towards the right in Northern hemisphere and towards left in Southern hemisphere.

        At some higher latitude, when isobars are straight an there is no frictional force, the pressure gradient force is balanced by Coriolis force and the resultant wind blows parallel to the isobars. This wind is known as Geostrophic wind.

In case of Circular pressure belts - 

• In Northern Hemisphere - Winds deflected towards right and forms cyclonic circulation in case of Low pressure zone and forms anti-cyclonic circulation in case of High pressure zone.
• In Southern Hemisphere - Winds deflected towards left and forms cyclonic circulation in case of Low pressure zone and forms anti-cyclonic circulation in case of High pressure zone.

Previous Article - Pressure & Pressure belts

Next Article - Planetary winds & ITCZ

Notes on other subjects

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Optional Notes

Public Administration

Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own. 

Hope! It will help you to achieve your dream of getting selected in Civil Services Examination 👍