What are the global winds?
Global winds or Planetary winds are large body air masses created mainly as a result of the earths rotation, the shape of the earth and the suns heating power. Global winds are caused by the combination of pressure belts and the Coriolis effect. Generally, winds are named based on the direction in which they flow, hence global or planetary winds blow from high-pressure belts to low-pressure belts. They blow over large areas of the globe (across continents and oceans) in the same direction throughout the whole year. Apart from the global wind, there are other types of winds that occur within certain localities such as seasonal winds, temporary winds, and local winds.
The curved surface of the Earth causes some parts of Earth to receive the Suns rays more directly than other parts. For example, the sun shines more directly on the surface at the equator than at the poles. As the warmer air over the equator rises, colder air from the poles rushes toward the equator to take its place. This steady exchange of warm and cold air that occurs between the equator and the poles produces global wind belts. Earths rotation causes the direction of the winds to deflect slightly: toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere. However, global winds push air masses around Earth and bring changes in the weather. For instance, in the United States, global winds called the prevailing westerlies to push air masses from west to east.
Global Winds Patterns
The Global winds patterns movement is also called the general circulation of the atmosphere.
Causes of global wind
- The rotation of the earth.
- Distribution of continents and oceans
- Uneven heating of earths surface the sun which causes pressure differences
- Differences in atmospheric pressure
Types of Global or planetary winds
- Trade wind
- Polar easterlies
The trade winds
Trade winds are the prevailing pattern ofeasterlysurface winds found in thetropicstowards the Earth’sequator; these are steady high-pressure winds that blow from 300 N and S and almost towards the equatorial low-pressure belt. The trade winds are very predictable and are called so because of their early use by sailors who solely relied on the winds to enable them to establish quick and reliableroutes across the vast Atlantic and, later, Pacific Oceans. The trade winds are formed when the suns rays fall vertically over the equatorial region, in this case, the air becomes hot and goes upwards. Since the pressure is less upward, the rising air gets space for expansion and consequently, the air becomes cool and very dense. The cool air could not come down directly due to warm air at the bottom. As a result, the air moves towards north and south directions through the upper atmosphere. On moving up to 300 latitudes, some part of this air finds its way to come down and blows towards the equatorial low-pressure belts.
According to Ferrels Law, the trade wind blows from north-east in the northern hemisphere and south-east in the southern hemisphere. Hence, the trade wind of the northern hemisphere is known as North-East Trade Wind and that of the southern hemisphere as South-East Trade Wind. Some of the characteristics of the trade winds show that the sky remains clear, the weather appears hot and dry as this trade wind originates in the high-pressure zones. For example, most of the famous deserts of the world such as the Libyan desert, the Sahara desert, the Arabian desert in the northern hemisphere and the Kalahari desert in the southern hemisphere are located very close to this area.
The trade winds act as thesteering flowfortropical cyclonesthat form over the world’s oceans.Trade winds also steer African dust westward across the Atlantic Ocean to create hazy sunsets in the Caribbean, as well as portions of southeast North America.
These are prevailing winds that blow from sub-tropical high-pressure belts towards sub-polar low-pressure belts between the tropical regions and the Arctic Circle or the Antarctic Circle. Westerlies are relatively more variable than the trade winds both in direction and intensity. There are more frequent invasions of polar air masses along with the traveling cyclones and anti-cyclones. The westerlies are stronger and persistent in the cold and in the southern hemisphere where there is less land to cause the flow to slow down. However, in the southern hemisphere, the maximum area is covered by the water bodies and hence the west wind can move uninterruptedly. In the northern hemisphere, the wind blows from the south-west and in the southern hemisphere from the north-west. The velocity of the westerlies reaches at the highest between 400 to 470 south latitude. This region is called Roaring Forties. furious fifties and screaming sixties along 40S, 50S, and 60S latitudes. This air movement is known as Brave West Winds.
the polar easterlies which are also known as Polar Hadley cells are the cold dense air that blows from the high-pressure areas of thepolar highsat thenorthandsouth polestowards the low-pressure areas within the Westerlies at high latitudes.These prevailing wind patterns are quite different from the westerlies as they are usually weak and irregular.When the low angle of the sun and cold air build-up and then subsideat the pole, they move to the surface of high-pressure areas, forcing the air to blow towards the equator, the outflow is deflected westward by the Coriolis effect.
How does the Coriolis force affect planetary wind?
Coriolis force is defined as the force that is exerted by the rotation of the earth. Coriolis force deflects the wind in the right direction in the northern hemisphere and to the left in the southern hemisphere. The deflection is more when the wind velocity is high. The Coriolis force is directly proportional to the angle of latitude. It is maximum at the poles and is absent at the equator.
Generally, winds do not move to cross the isobars at right angles as the pressure gradient directs them. They get deflected from their original direction. One of the most unique influences on wind direction is the deflection caused by the earths rotation on its axis. This deflection is always to the right of the direction of motion in the northern hemisphere and to the left in the southern hemisphere. This deflection of wind is referred to Coriolis force, it affects all types of winds and not just global or planetary winds; Coriolis force was given the name by a French physicist in 184
Effects of Global Winds
Many effects are associated with high winds, these also depend on the magnitude of their velocity and pressure differential. Some of the effects of Global/ planetary winds are explained below.
- As the wind blows from high-pressure belts towards the low-pressure belts, the climate of places along their paths are usually affected. The movement of the wind brings about changes in temperature and humidity; this, therefore, determines the type of precipitation that may occur.
- The wind is a major factor that affects weather and climate. The wind carries heat, moisture, pollutants, and pollen grains from one place to another. For instance, as the wind blows over the top of a mountain, it brings moisture with it, whichcondenses as rain and other forms of precipitations before coming over the base of the mountain.
- One of the main causes of erosion is the wind, wind can move small rock particles or soil fragments from one place to another. This can take place in arid areas where there is little or no vegetation, sometimes in dry areas where there is insufficient rainfall to support vegetation growth.
- The wind has been a source of energy for so many years, it has been used to push ships around the world and its captured inwindmills to pump water. However, in our contemporary time, wind energyis used to generateelectricityfor both household industrial uses.
- The wind has the ability to erode and change the natural landscape into stunning shapes, this can be seen in the Altiplano region of South America, another example is the formation of sanddunes on a beach or in a desert environment.
- Very strong wind speed ranging from 25 miles per hour (40km/h) to 40 miles per hour (64km/h) can cause extensive damage to plant seedlings because it ruptures plant cells, making them vulnerable to evaporation and drought
- Planetary winds also generate sound; high winds may produce howling sounds of varying frequencies. For instance, natural objects like leaves, and trees can be lifted in the air by wind movement. These objects will produce sound if they touch each other. Sometimes, a soft wind could lead to a low level ofenvironmental noise.
- Wind speeds can lead to power outages due to tree branches disrupting the flow of energy through power lines.
- Different species of trees especially those with shallow roots are more prone to uproot during very high wind speed.
- Wind dispersal of seeds is another important function of planetary wind, even though its one of the primitive methods. This system of dispersal can take different forms; the seeds can float on the breeze and land in a site suitable forgermination or they can as well flutter to the ground.
- Animals like sheep and cattle are affected by wind chill caused by a combination of wind and cold temperatures, very cold wind renders their wools and hair coverings ineffective.