Published on 31 Jan 2025
Planetary winds are large-scale wind patterns that blow across the Earth's surface, driven by the unequal heating of the Earth by the Sun. they are also called prevailing winds and they maintain same direction throughout the year. Trade winds, Westerlies and Polar Easterlies constitute the planetary wind system.
Trade winds
These are winds that blow from the sub-tropical high-pressure areas towards the equatorial low-pressure belt.
Location: From the equator (0°) to 30° latitude in both hemispheres between sub tropical high pressure belt to the equatorial low pressure belt.
Direction: From both hemispheres, these winds blow from east to west.
Alternate names: In the Northern Hemisphere, they are known as the Northeast Trades, and in the Southern Hemisphere, they are the Southeast Trades.
Features: They are stable and descending in areas of its origin and becomes humid and warmer as they reach the equator by picking up moisture. The eastern parts of the trade winds associated with the cool ocean currents are drier and more stable than the western parts of the ocean
Precipitation: They bring heavy precipitation on the eastern coast of the continents.
Cyclonic: Trade winds are often associated with cyclonic depressions
Deserts: Offshore in west coast and thus form some of the hot deserts of the world.
Example: Sahara, Atacama etc.
Mechanism and origin of trade winds
Hadley cell mechanism: It is a closed circulation loop where the warm moist air from equator rises and descends at about high pressure areas along 300 N/S latitude. This descending air travels equatorially through the surface forming trade winds.
Coriolis force: Flow of the descending air is deflected towards right in the northern hemisphere and towards left in the southern hemisphere by the Coriolis effect.
Direction: Due to deflection caused by Coriolis force, trade winds blow majorly from northeast in the northern hemisphere and southeast trade winds in the southern hemispheres.
Significance of trade winds
Maritime trade routes: trade winds allows navigation by sailing of vessels by its steady and strong nature. . These reliable winds facilitated safer and more efficient long-distance sea voyages.
Example: European sailors used the Northeast Trade Winds to navigate from Europe to the Americas, and the Southeast Trade Winds for the return journey.
On weather patterns and rainfall: The trade winds play a crucial role in the formation of rainforests near the equator. As the winds converge near the equator, they bring moist air from the ocean.
Example: Contributing to the lush vegetation in regions like the Amazon Rainforest and the Congo Basin.
On ENSO: : During El Niño events, the trade winds weaken, leading to changes in sea surface temperatures and atmospheric conditions and in La Niña events, strengthened trade winds can have contrasting effects.
On tourism: Many of the most famous tourist locations are in this belt due to its pleasant temperature and weather.
Global warming: rainfall brought about by trade winds enhances the vegetation growth which in turn captures carbon from the atmosphere and thus reducing effect of global warming.
Westerlies
Westerlies blows from the sub-tropical high-pressure belts towards the sub polar low-pressure belts. These winds blow from southwest to north-east in the northern hemisphere and north-west to south-east in the southern hemisphere.
Location: Between about 30° and 60° latitude.
Direction: These winds flow from west to east in both hemispheres. They originate at high pressure horse latitude and move towards poles. Because of the influence of Coriolis force, they become the south westerlies in the northern hemisphere and Northern westerlies in the southern hemisphere.
Anomalies: Compared to northern hemisphere velocity of westerlies are high in southern hemisphere. This is because there is more ocean and less land mass in southern hemisphere than northern hemisphere
Precipitation: They bring heavy precipitation on western coast between 40o – 600 north and south latitudes. These are referred as roaring 40s, furious 50s, shrieking 60s.
Ocean currents: Since westerlies are strong in southern hemisphere, the ocean currents which are drawn by westerlies are also strong compared to that of ocean currents in northern hemisphere.
Seasonal variation: During winters and at times of low pressure over the poles, westerlies become strongest. They becomes weaker during summers and when pressure is high at poles.
Cyclones: Westerlies drives the extra-tropical cyclones in the middle latitudes from west to east.
Effects of westerlies
Weather Patterns: Westerlies drive eastward-moving weather systems, influencing storm paths and precipitation distribution in the mid-latitudes.
Temperature Regulation: Westerlies moderate temperatures by bringing maritime air, preventing extreme fluctuations in the mid-latitudes.
Ocean Currents: Westerlies drive ocean currents, like the North Atlantic Drift, affecting the climate of regions such as Western Europe.
Trade Routes: Historical trade routes often followed westerlies, utilizing prevailing wind patterns for efficient ocean navigation.
Nutrient transportation: Antarctic Circumpolar Current which are driven by westerlies transports enormous volumes of cold, nutrient-rich water to the ocean, creating healthy marine ecosystems and food webs.
Regional oceanography: The intensity of westerlies strengthens certain ocean current leakages. Over the South Atlantic and Indian Ocean, the westerlies play a crucial role in driving regional oceanography around southern Africa.
Issues associated with westerlies
Extreme weather events: Intensified westerlies can contribute to the occurrence of extreme weather events, including storms, heavy precipitation, and related hazards.
Droughts and dry spells: Alterations in the intensity and position of the Southern Hemisphere Westerly (SHW) winds have been associated with occurrences of continental droughts and wildfires.
Disruption of flight paths: While westerlies generally benefit aviation by providing tailwinds, intense and turbulent westerlies can lead to disruptions in flight paths and affect air travel.
Sea level rise: Antarctic sea ice extent alterations involve the deterioration of ice shelves bordering West Antarctica and the Antarctic Peninsula. This results from increased basal melting attributed to warming along the Antarctic Peninsula
Impact on agriculture: Unpredictable westerly patterns can affect agriculture by influencing precipitation and temperature, potentially leading to unfavourable conditions for crops.
Polar easterlies
Location: Between about 60° latitude and the poles.
Direction: These winds blow from east to west, forming a polar cell.
Alternate names: In the Northern Hemisphere, they are the Polar Easterlies, and in the Southern Hemisphere, they are the Polar Easterlies.
Characteristics: These are cold and dry winds and is highly variable in nature.
Geography
Planetary winds
Trade winds
Westerlies
Polar Easterlies
prevailing winds
Mechanism and origin of trade winds
Significance of trade winds
Effects of westerlies
Issues associated with westerlies
Polar easterlies
General Studies Paper 1
Physical Geography
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