Wind in simple terms is nothing but moving air. We all enjoy wind rustling through the leaves in our garden. It has also expanded the range of transport and has provided a power source in terms of mechanical energy for the generation of electricity in windmills and recreation purposes in hot air balloons. Wind power was also used in voyages by sailors to direct their ships. When the winds are strong, they lead to the destruction of life and property in the form of cyclones and storms, causing forest fires, landslides etc. In this article, we will learn about the causes of wind and the destruction caused by winds.
Types of Wind
Wind blowing above the earth surface may be classified into five major types:
- Planetary winds
- Trade winds
- The westerlies
- Periodic winds
- Monsoon winds
- Land breeze
- Sea breeze
- Mountain and valley breeze
- Local winds
Planetary winds comprise winds distributed throughout the lower atmosphere. The winds blow regularly throughout the year confined within latitudinal belts, mainly in north-east and south-east directions or from high-pressure polar-regions to low-pressure regions.
These winds are also known as tropical easterlies and blow from the right in Northern hemisphere and to the left in the Southern hemisphere due to Coriolis effect and Ferrel’s law. They start blowing from the sub-tropical high-pressure areas towards the equatorial low-pressure belt. In the Northern hemisphere, they blow as northeastern trades and in the Southern hemisphere, they blow as southeastern trades.
These winds are also known as Shrieking Sixties, Furious Fifties, and Roaring Forties. They blow from the subtropical high-pressure belts towards sub-polar low-pressure belts. The westerlies of Southern hemisphere are stronger and constant than the westerlies of Nothern hemisphere.
These winds change their direction periodically as there is a change in the seasons. Following are the types of periodic winds:
- Monsoon winds: The temperature difference created due to the Indian Ocean, Arabian Sea and Bay of Bengal on one side and the Himalayan wall on the other forms the basis of monsoons in the Indian subcontinent.
- Land breeze: These winds blow from land to sea, carrying no moisture but dry and warm.
- Sea breeze: These winds blow from sea to land, carrying some moisture.
- Mountain and valley breeze: Valley breeze is the hot air blowing from the valley which flows up to the slopes of mountain slopes. While mountain breeze is the reverse of the valley breeze that is the cold air from the mountain flow towards the valley.
The local winds include the sea and the land breeze created due to the pressure difference between the air over the sea and the land regions. Loo is the local winds that blow in the northern part of India.
How is Wind Measured?
The wind has speed as well as direction. To measure these two parameters two different devices are used and they are as follows:
These instruments are a common weather station instrument which is used for measuring the speed of the wind. Cup anemometer, hotwire anemometer, windmill anemometer, sonic anemometer, and Laser Doppler anemometer are the different types of anemometer.
- Wind vanes
These devices are also known as weathervane which is used for determining the direction of the wind.
Causes of Wind
The main cause of generation of wind is the uneven heating of two regions. Following are the examples of uneven heating we see around us:
What is uneven heating between land and sea?
Seawater gets heated more slowly as compared to land. As the temperature of the land rises, the air above it gets heated by conduction. The density of warm air is less than the surrounding environment, because of which it rises, creating a vacuum in its place. The cooler air from the sea rushes to fill the vacuum which creates a cool coastal breeze. At night, the land cools off more quickly, which creates a temperature difference between the temperature onshore and that offshore. Because of this temperature difference, again a pressure drop is created establishing a land breeze.
The flow of Air between Land and Sea
What is uneven heating between equator and pole?
The equatorial and tropical regions (close to the equator) get the maximum heat from the sun; hence they get hotter than the polar regions. The air surrounding this region gets heated up and rises to create a vacuum. Cooler air from the poles rushes to fill the vacuum. The wind does not flow in the north-south direction because a change in direction is caused by the rotation of the earth.
The flow of Air between Equator and Pole