Ships relied on trade winds to establish quick, reliable routes across the vast Atlantic and, later, Pacific Oceans. They have been instrumental in the history of exploration, communication, and trade. Trade winds are generally very predictable. Trade winds are the powerful prevailing winds that blow from the east across the tropics. Even strong winds are often short in duration. The prevailing winds at the horse latitudes vary, but are usually light. Many deserts, from the rainless Atacama of South America to the arid Kalahari of Africa, are part of the horse latitudes. Horse latitudes are about 30 and 35 degrees north and south. The horse latitudes are a narrow zone of warm, dry climates between westerlies and the trade winds. The ACC is the largest ocean current in the world, and is responsible for transporting enormous volumes of cold, nutrient-rich water to the ocean, creating healthy marine ecosystems and food webs. In fact, another name for the Antarctic Circumpolar Current is the West Wind Drift. Driven by westerlies, the powerful Antarctic Circumpolar Current (ACC) rushes around the continent (from west to east) at about 4 kilometers per hour (2.5 miles per hour). Westerlies have an enormous impact on ocean currents, especially in the Southern Hemisphere. The westerlies of the Roaring Forties were very important to sailors during the Age of Exploration, when explorers and traders from Europe and western Asia used the strong winds to reach the spice markets of Southeast Asia and Australia. The tip of South America and Australia, as well as the islands of New Zealand, are the only large landmasses to penetrate the Roaring Forties. Throughout the Roaring Forties, there are few landmasses to slow winds. The strongest westerlies blow through the “Roaring Forties,” a wind zone between 40 and 50 degrees latitude in the Southern Hemisphere. Westerlies are strongest in the winter, when pressure over the pole is low, and weakest in summer, when the polar high creates stronger polar easterlies. They are fed by polar easterlies and winds from the high-pressure horse latitudes, which sandwich them on either side. Westerlies are prevailing winds that blow from the west at midlatitudes. Polar easterlies flow to low-pressure areas in sub-polar regions. They emanate from the polar highs, areas of high pressure around the North and South Poles. Polar easterlies are dry, cold prevailing winds that blow from the east. The Earth contains five major wind zones: polar easterlies, westerlies, horse latitudes, trade winds, and the doldrums. (In the Southern Hemisphere, low-pressure systems will be on your right.) In 1857, Dutch meteorologist Christoph Buys Ballot formulated a law about geostrophic winds: When you stand with your back to the wind in the Northern Hemisphere, low pressure is always to your left. The Coriolis effect causes some winds to travel along the edges of the high-pressure and low-pressure systems. The Coriolis effect makes wind systems twist counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. This happens because Earth’s rotation generates what is known as the Coriolis effect. Generally, prevailing winds blow east-west rather than north-south. Areas where prevailing winds meet are called convergence zones. Prevailing winds are winds that blow from a single direction over a specific area of the Earth. The complex relationships between fronts cause different types of wind and weather patterns. The boundary between these two areas is called a front. Winds generally blow from high-pressure areas to low-pressure areas. At the same time, cooler, denser air moves over Earth’s surface toward the Equator to replace the heated air. Warm equatorial air rises higher into the atmosphere and migrates toward the poles. At the Equator, the sun warms the water and land more than it does the rest of the globe. Landforms, processes, and impacts of wind are called Aeolian landforms, processes, and impacts.ĭifferences in atmospheric pressure generate winds. It is the great equalizer of the atmosphere, transporting heat, moisture, pollutants, and dust great distances around the globe. It is strong enough to carry sailing ships across the ocean and rip huge trees from the ground. It can dry your clothes in summer and chill you to the bone in winter.
It does not have much substance-you cannot see it or hold it-but you can feel its force. Wind is the movement of air caused by the uneven heating of the Earth by the sun.