Earth Science: Atmosphere – Wind, Storms, and Anomalies
Wind is air in motion originating from air pressure gradients in the atmosphere. It always blows from an area with high air pressure into an area with low air pressure. The greater the difference in air pressure, the stronger the wind.
There are several parallel zones on the Earth with prevailing surface winds. Warm air expands near the Equator and rises, causing a low- pressure belt called the intertropical convergence zone. This zone is also known as the doldrums. While the rising air cools slowly, it expands toward the Earth’s Poles, creating convection currents. The air descends again in the subtropical horse latitudes, which are located at 30° north and south of the Equator. Here, the air merges into the trade and westerly winds.
The horse latitudes experience only light winds or calm air, similar to the doldrums. Trade winds blow near the Earth’s sur- face and toward the Equator, replacing the rising air. They merge with the low-pressure system of the intertropical convergence zone and the cycle repeats. In contrast, westerly winds collide in the temperate regions with cold air masses called the polar easterly winds. The Poles are regions with high air pressure caused by the sinking cold and dense air.
Local winds
The formation of winds is affected by local geography, such as mountains, deserts, terrestrial areas, and oceans. Therefore, many areas experience localized winds in addition to the large-scale wind systems. Coastal areas experience offshore and onshore winds depending on the daily warming of the atmosphere.
Drainage or katabatic winds may occur on the lee side of mountains. In contrast, the mistral is a very cold and dry wind blowing from the high ranges of the French Massif Central. The sirocco is known as a hot and dry wind in the northern parts of the Sahara.
Heavy storms
Heavy storms with spiraling winds are frequently generated above warm tropical oceans. They are called hurricanes in the Caribbean, typhoons in the China Sea, and cyclones in the Indian Ocean. They move west reaching velocities of up to 186 miles per hour (300 km/h).
Tornadoes are smaller and short-lived, but those generated from thunderstorm clouds are just as dangerous. The Beaufort scale, named after the British admiral Sir Francis Beaufort (1774-1857), is used to indicate the force of wind.
CORIOLIS FORCE
Winds do not blow across the globe in a straight line; they are diverted from the west to the east by the rotation of the Earth, causing the distinctive spiral effect.
This rotation causes the rising warm air masses from the Equator to the Poles to shift to-ward the right and the descending cold air masses from the Poles to the Equator to shift toward the left. This effect was discovered by the French physicist Gaspard Gustave Coriolis (1792-1843).