It is the movement of air from the high-pressure area to the low-pressure area having both speed and direction. It is made up of gusts and eddies that can only be felt and not seen, unlike rain and snow in the swaying of trees, cool push against us making hair fly, dry leaves flying etc. There are three types of winds namely- Permanent Wind, Seasonal Wind, Local Wind.
The winds that flow throughout the year from one latitude to another latitude because of latitudinal differences in the air pressure are called planetary winds. They are also called prevailing winds. Planetary winds blow from a single direction over a specific area over the earth.
The areas in which the planetary winds meet are called convergence zones. They generally blow east to west rather than blowing north to south. This usually happens because the earth’s rotation generates the Coriolis effect. The Coriolis effect makes wind systems twist anticlockwise in the Northern hemisphere and clockwise in the southern hemisphere.
Planetary winds also known as permanent winds and are being controlled by the pressure belts, located at the lower part of the atmosphere and blow towards the same direction throughout the whole year. In other terms, they are also called primary winds or prevailing winds. They blow in the direction from high pressure to low pressure. The planetary wind is of three types namely, - the trade wind, the westerlies and the polar wind.
Classification of Winds
The wind is the movement of air. It is caused by the uneven heating of the Earth by the sun and the Earth’s own rotation. Winds have a vast range - from light breezes to natural calamities such as cyclones and hurricanes. Differences in atmospheric pressure cause winds. It is a general property of air that warm air rises up and dense and cool air moves towards downwards. At the equator, the sun heats water and land more than anywhere else on the globe. As a result, the warm equatorial air rises high into the atmosphere and migrates towards the poles. Similarly, the cool and dense air moves over the Earth’s surface towards the equator to replace the heated air.
The winds are classified based on global and local phenomena. On Earth, three types of winds exist - Primary Winds, Secondary Winds, and Tertiary Winds. Winds can either be permanent or temporary. Primary winds are the permanent winds. Planetary winds are the primary winds. Secondary winds are seasonal or periodic winds. Types of secondary winds are - The Monsoon Winds, The Sea and Land Breeze, and the Mountain and Valley Breeze. The tertiary or local winds cover only small areas. Different types of tertiary winds are - Blizzards, Chinooks, Santa Ana, Etesian, or Meltemi.
Types of Planetary Winds
In the planetary wind system, there are three main types of planetary winds - The Trade Winds, The Westerlies, and The Easterlies.
The Trade Winds
The sun's rays fall vertically on the equator which causes the air to heat up, and it rises upwards. Due to the low upward pressure, the rising air has room to expand, resulting in cold and dense air. Due to the warm air on the ground, the cold air could not go straight down. As a result, air travels north and south through the upper atmosphere. At altitudes up to 30°, some of this air comes down and blows towards the low-pressure belt on the equator. This part of the air is known as the trade winds. According to Ferrell's Law, trade winds blow from the northeast in the northern hemisphere and from the southeast in the southern hemisphere. They are called tropical easterlies as well.
Points to remember
The trade winds blow in a belt that lies between 5°N to 30°N in the northern hemisphere and 5°S to 30°S in the southern hemisphere.
It is known to all that the wind travels from high pressure to low pressure. There is low pressure on the equator and high pressure on the subtropics. Hence, the air moves towards the equator from the subtropics. Because the earth’s rotation generates a Coriolis effect, the wind moves from the left side in the southern hemisphere to the right side in the northern hemisphere.
The latitude of 30°- 35°N and 30°- 35°S are the areas where the air is descending and is characterised by calm and light variable winds. These winds are comparatively dry and the weather condition is quiet and stable. This latitude zone is called Horse latitude.
Some of the air from latitude 30 ° blows toward the poles on the surface of the earth, reaches latitude 60 ° and is then exposed to the cold, dense air coming from the poles. In comparison, warm, light air from the tropics rises above the dense, cold polar air and blows partially towards the polar low-pressure belt; this wind is called westerly wind. It blows from the southwest in the northern hemisphere and from the northwest in the southern hemisphere. Due to the large land area in the Northern Hemisphere, there are some local changes in air movement. However, in the Southern Hemisphere, the largest area is covered with water, so you can move unimpeded by the westerly wind. Westerlies speeds reach their highest between 40 ° S and 50 ° S. This area is called the Roaring Forties and the movement of air is known as Brave Westwinds.
Points to remember
The westerlies blow in the latitude belt of 30°- 60° N and 30°- 60° S.
The air streams that flow towards the poles from the subtropical high-pressure areas deflect towards the east in the northern hemisphere to form south-westerlies.
The air streams that flow towards the poles from the subtropical high-pressure areas deflect towards the east in the southern hemisphere to form north westerlies.
Contrary to the trade winds, the westerlies are very much variable in both force and direction, especially in the northern hemisphere.
In the southern hemisphere, the westerlies blow with great strength and are regular throughout the year over the ocean. In the southern hemisphere, between the latitude 40° - 50° S, the westerlies have got the name of Roaring Forties.
These winds sometimes give a roaring sound because of their high speed.
The Easterlies or the Polar Easterlies
The polar easterlies are the dry, cold prevailing winds that blow from the high-pressure areas of the polar region and south poles towards low-pressure areas within the Westerlies at high latitudes. Cold air sinks to the poles, creating high pressures that allow the air to escape south (north of the Southern Hemisphere) toward the equator. They are very cold winds that do not cause rainfall. These prevailing winds then blow from east to west, as this outflow is diverted west by the Coriolis effect. The wind comes from the east, so it is called the easterlies. Unlike mid-latitude westerlies, polar easterlies are often weak and irregular.
Points to remember
They blow from the Polar high-pressure area to the temperature low-pressure area.
Towards the equator, they are deflected towards the west in the northern hemisphere to form north easterlies and in the southern hemisphere to form south easterlies.
The understanding of Wind and it’s type is an important aspect to doing social-sciences right. Conceptual clarity changes the learning procedure as well as a student’s point of view on the subject matter.