In many myths the winds are personified and often deified, reflecting their importance in agricultural and seafaring societies.
The Mysteries of Earth Science: The World Winds
The differences in air temperature will create winds. When hot air rises, its creating a low-pressure area. Similarly, when the cold air sinks, its creating a high-pressure area. Air is pushed out of high-pressure areas towards low-pressure areas.
The movement of air from high-pressure to low-pressure areas follows a basic worldwide pattern. Winds blow from the Equator towards the Poles, or from the Poles towards the Equator, but Earth’s rotation deflects these sideways, a phenomenon known as the Coriolis effect.
Wind direction is the direction from which the wind blows. The prevailing wind is the most frequent wind direction in an area.
Monsoons are sudden seasonal reversals in wind direction. They bring heavy rain.
Hot air rises in the Tropics and spreads north and south towards the Poles. Because of the Earth’s rotation, the air does not travel in a straight line but is deflected-to the right (clockwise) in the Northern Hemisphere, to the left (anti-clockwise) in the Southern Hemisphere. This is called the Corioli effect, after Frenchman Gustave-Gaspard de Coriolis (1792-1843) who first described the phenomenon.
The Coriolis force also affects the rotation of ocean currents. It increases in force from the Equator to the Poles.
Global Wind Patterns
Each hemisphere has three wind system: tropical trade winds, mid-latitude westerlies, and polar easterlies. Hot air rises at the Equator and travels north and south. When it reaches latitude 30 Celsius north and south, known as the horse latitude, it sinks, creating high-pressure areas. Some of this air travels back towards the Equator, and these air flows are known as the trade winds. They die out at the Equator, creating an area of calm, light winds known as the doldrums. The westerlies are eastward-moving winds that blow from the horse latitudes towards the Poles. At around 60 Celsius north and south they meet the polar easterlies, cold winds that blow out from high-pressure areas at the Poles. The westerlies and polar easterlies meet at the polar front. The difference in temperature causes warmer air to rise, and most of it goes back towards the Equator.
The Worlds Winds
In the Tropic the trade winds blow toward the Equator, from the north-east in the Northern Hemisphere and from the south-east in the Southern Hemisphere. In the mid-latitudes, the westerlies blow from the north-west and south-west towards the Poles. In the Polar Regions, the polar easterlies blow from north-east and south-east towards the Equator.
The strongest occur in southern Asia, northern Australia and Africa.
In winter air over Siberia cools and sinks, causing a high-pressure area north of the Himalayas. This in turn creates winds that blow across India and out over the India Ocean.
In summer the high pressure over Siberia weakens and a low-pressure area takes its place. This draws in moisture-laden air from the Indian Ocean, but its progress north is blocked by the Himalayas, producing heavy rain over the Indian subcontinent.
Floodwaters from the seasonal Indian monsoon inundate a river basin and the surrounding field systems.
Cold, dry air descends north of the Himalayas. Warm air rises over the Indian Ocean and draws in colder air from the land.
Warm air rises, creating a low-pressure area north of the Himalayas, and moisture-laden air is drawn in form the Indian Ocean.
Myths and Legends
In many myths the winds are personified and often deified, reflecting their importance in agricultural and seafaring societies. The Ancient Greeks had Bores (North Wind) and Zephyrus (West Wind), ruled by the minor god Aeolus. To the Sumerians, the wind was the breath of Enlil. The Aztec wind god Ehecatl was worshipped in round building, which offered no sharp corners to the wind. Other wind deties include Celtic goddess Dana and Mayan god Huracan (From which we get hurricane).
Meandering bands of fast-moving westerlies, called jet streams, develop high in the atmosphere above polar and subtropical areas, at heights of 10-15km (6-9 mile), where large differences in temperature and air pressure occur. They can reach speeds of 300km/h (200mph), but average about 130km/h (80mph) in summer and 70km/h (40mph) in winter.