Types Of Winds: Planetary winds

Introduction

• Planetary winds are the winds that flow year-round from one latitude to another due to latitudinal changes in air pressure. Additionally, they are referred to as prevailing winds. 
• Prevailing winds blow in a single direction over a particular region of the globe.
• Convergence zones are the areas where the planet’s winds meet. They are more likely to blow east to west than north to south. This is often the case due to the Coriolis effect caused by the earth’s rotation. The Coriolis effect causes wind systems in the Northern Hemisphere to twist anticlockwise and clockwise in the Southern Hemisphere.
• These pressure belt-controlled winds blow in the same direction throughout the year. The planetary wind is classified into three types: trade winds, westerlies, and polar winds. 

Trade Winds (Tropical Easterlies)

• The sun’s rays fall vertically across the equatorial region, causing the air to heat up and rise. Because the pressure is lower upward, the rising air has more room to expand, and the air becomes cooler and denser.  
• Due to the presence of warm air at the bottom, the cool air could not descend directly. As a result, air moves north and south in the upper atmosphere. Up to 30° latitudes, some of this air descends and blows toward the near the equator low pressure belt. This section of air is referred to as the Trade Wind. 
• Ferrel’s Law states that the trade wind blows from north-east to south-west in the northern hemisphere and south-east to north-west in the southern hemisphere.
• The northern hemisphere’s trade wind is referred to as the North-East Trade Wind, while the southern hemisphere’s trade wind is referred to as the South-East Trade Wind. Because this trade wind originates in high pressure zones, the sky remains clear and the weather is hot and dry. 
• The world’s great deserts are located closer to this area. For instance, the Sahara desert, the Libyan desert, the Arabian desert, and the Kalahari desert can all be mentioned in the northern hemisphere.

Thus, the primary characteristics are as follows:

• Wind gusts from the subtropical area of high pressure to the equatorial area of low pressure (Extremely steady winds)
• As they travel from high to low latitudes, they gradually become hot and dry, resulting in a high capacity to retain moisture.
• They cause considerable rainfall on eastern fringes of the land masses as they get humidity after blowing over oceans
• These winds collide near equator & form ITCZ, Here these winds starts to rise & induces heavy rainfall

The Westerlies 

• From 30° latitude, a portion of the air blows towards the poles across the surface of the earth, and upon reaching 60° latitude, it encounters the cold, dense air coming from the poles. Thus, the tropical air rises above the dense cold polar air and a portion of it blows towards the polar low pressure belt. This is referred to as West Wind

• It blows from the south-west in the northern hemisphere and from the north-west in the southern hemisphere. Because the northern hemisphere’s landmass is larger, some changes in air movement occur locally. However, in the southern hemisphere, the water bodies cover the greatest area, allowing the west wind to travel uninterrupted. 

• The westerlies reach their maximum velocity between 40° and 47° South latitude. This region is referred to as the Roaring Forties. This airflow is referred to as Brave West Winds. Two additional air masses circulate regularly between the north and south polar high belts and the subpolar lows. These are referred to as the north-east and south-east polar winds, respectively. Between the equator and the poles, the planetary wind system circulates (the trade winds, the westerlies, and the polar winds).   

The westerlies’ primary characteristics can be summarized as follows:

• Winds blowing from subtropical high pressure belts to low pressure belts in the subtropics
• Due to the Coriolis effect, in the Northern Hemisphere, the wind blows from S – W to N – E and in the Southern Hemisphere, the wind blows from N – W to S – E.
• Winds blowing from lower to higher latitude cause significant rainfall, particularly on the continents’ western margins. 
• Due to fewer obstructions from continents, the S – Hemisphere winds are more consistent in direction and blow with greater force. 
• Additionally referred to as brave winds, roaring forties, furious fifties, and shrieking sixties, depending on the severity of the storms in the latitudes where they blow.
• It should be noted that not all of the temperate zone’s western coast (30* – 60*) receives year-round Westerlies due to the shifting of wind belts caused by the earth’s inclination.

Polar breezes (Polar Easterlies)

• The polar easterlies are the dry, cold predominant winds that blow from the high-pressure zones of the polar highs at the north and south poles towards low-pressure areas within the Westerlies at higher elevations. 
• Cold air sinks at the pole causing the high pressure, driving a southerly (northward in the southern hemisphere) discharge of air towards the equator. This outflow is then redirected westward by the Coriolis force
• Hence these predominant winds blow from the east to the west. Since the winds begin in the east, they are thus known as easterlies. Unlike the westerly winds in the mid – latitudes, the polar easterlies are generally feeble and erratic.

So, Major Features may be brought out as following

• Winds moving from polar high to sub polar low pressure belt
• Are quite frigid in nature since originate in arctic zones & do not bring much rainfall
• These winds give rise to hurricanes when they get in touch with westerlies
• Draws rapid shift in seasonal changes & brings heavy downpours

Wind System of the Monsoon

• The monsoon season is a shift in the seasons.
• Monsoon winds usually originate in regions of cold and high pressure.
• Monsoon winds are a seasonal feature of tropical and mid-latitude coastal regions’ year-round cycle of uneven heating and cooling.

Breezes from the Sea and Land

• Coastal locations generate both sea and land breezes.
• They form during the day as a result of the thermal and pressure gradient that exists between the sea and the land.
• The sea cools and heats slowly due to its high specific heat, whereas land rapidly heats and cools due to its low specific heat.
• During the day, the wind blows from sea to land, which is referred to as the sea breeze; at night, the wind blows in the opposite direction, which is referred to as the land breeze.

Breeze from the Mountains and Valleys

• Mountain and valley breezes resemble sea and land breezes in mountain regions.
• Because the valleys are hotter than the mountains during the day, air flows upward towards the slopes – from the valley to the mountains, which is referred to as Valley Breeze.
• At night, air flows down from the mountain peaks into the valleys, creating what is known as the mountain breeze.

Tertiary Winds or Local Winds

• Tertiary or local winds sweep across small areas. 
• local winds are formed as a result of changes in the surrounding temperature and pressure.
• In India,  one of the most common examples of local winds is loo.

Conclusion

• The term “prevailing winds” refers to winds that blow constantly in a particular direction over a specific region of the Earth.
• Prevailing winds fluctuate according to latitude on Earth because of variables such as unequal heating from the Sun and the Earth’s rotation.
• Prevailing winds are critical in selecting where wind farms should be located to produce power. 
• Predominant winds also influence the amount of rainfall received by various regions. These Prevailing winds result in the production of monsoons and deserts in Southeast Asia. 
• Due to prevailing winds, the west coasts of South and North America receive an abundance of rain during the winter.