What is the difference between trade winds and westerlies

Morgan is the last of an American whaling fleet that once numbered more than 2, vessels. Ships like the Morgan often used routes defined by the trade winds to navigate the ocean. Known to sailors around the world, the trade winds and associated ocean currents helped early sailing ships from European and African ports make their journeys to the Americas. Likewise, the trade winds also drive sailing vessels from the Americas toward Asia.

Even now, commercial ships use "the trades" and the currents the winds produce to hasten their oceanic voyages. How do these commerce-friendly winds form? Between about 30 degrees north and 30 degrees south of the equator, in a region called the horse latitudes , the Earth's rotation causes air to slant toward the equator in a southwesterly direction in the northern hemisphere and in a northwesterly direction in the southern hemisphere.

This is called the Coriolis Effect. The Coriolis Effect, in combination with an area of high pressure, causes the prevailing winds—the trade winds—to move from east to west on both sides of the equator across this degree "belt.

As the wind blows to about five degrees north and south of the equator, both air and ocean currents come to a halt in a band of hot, dry air. This degree belt around Earth's midsection is called the Inter-Tropical Convergence Zone , more commonly known as the doldrums. Intense solar heat in the doldrums warms and moistens the trade winds, thrusting air upwards into the atmosphere like a hot air balloon.

Winds generally blow from high-pressure areas to low-pressure areas. The boundary between these two areas is called a front. The complex relationships between fronts cause different types of wind and weather pattern s. Prevailing wind s are winds that blow from a single direction over a specific area of the Earth. Areas where prevailing winds meet are called convergence zone s. Generally, prevailing winds blow east-west rather than north-south.

The Coriolis effect makes wind systems twist counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The Coriolis effect causes some winds to travel along the edges of the high-pressure and low-pressure systems.

These are called geostrophic wind s. In , 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. In the Southern Hemisphere, low-pressure systems will be on your right. Wind Zones The Earth contains five major wind zones: polar easterlies, westerlies, horse latitudes, trade winds, and the doldrums.

Polar Easterlies Polar easterlies are dry, cold prevailing winds that blow from the east. They emanate from the polar high s, areas of high pressure around the North and South Poles.

Polar easterlies flow to low-pressure areas in sub-polar regions. Westerlies Westerlies are prevailing winds that blow from the west at midlatitude s. They are fed by polar easterlies and winds from the high-pressure horse latitudes, which sandwich them on either side. 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.

Throughout the Roaring Forties, there are few landmasses to slow winds. 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. 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.

Westerlies have an enormous impact on ocean current s, especially in the Southern Hemisphere. Driven by westerlies, the powerful Antarctic Circumpolar Current ACC rushes around the continent from west to east at about 4 kilometers per hour 2. 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.

Horse Latitudes The horse latitude s are a narrow zone of warm, dry climate s between westerlies and the trade winds. Horse latitudes are about 30 and 35 degrees north and south.

Many deserts, from the rainless Atacama of South America to the arid Kalahari of Africa, are part of the horse latitudes. The prevailing winds at the horse latitudes vary, but are usually light. Even strong winds are often short in duration. Trade Winds Trade wind s are the powerful prevailing winds that blow from the east across the tropics.

Trade winds are generally very predictable. They have been instrumental in the history of exploration, communication, and trade. Ships relied on trade winds to establish quick, reliable route s across the vast Atlantic and, later, Pacific Oceans.

Even today, shipping depends on trade winds and the ocean currents they drive. In , Norwegian explorer Thor Hyerdahl and a small crew used trade winds to travel from the coast of Peru to the coral reefs of French Polynesia, more than 6, kilometers 4, miles , in a sail-powered raft. The expedition, named after the raft Kon-Tiki aimed to prove that ancient mariners could have used predictable trade winds to explore wide stretches of the Pacific.

Trade winds that form over land called continental trade winds are warmer and drier than those that form over the ocean maritime trade winds. The relationship between continental and maritime trade winds can be violent. Most tropical storm s, including hurricanes, cyclones, and typhoons, develop as trade winds.

Differences in air pressure over the ocean cause these storms to develop. As the dense, moist winds of the storm encounter the drier winds of the coast, the storm can increase in intensity. Strong trade winds are associated with a lack of precipitation , while weak trade winds carry rainfall far inland. The most famous rain pattern in the world, the Southeast Asian monsoon, is a seasonal, moisture-laden trade wind.

Besides ships and rainfall, trade winds can also carry particles of dust and sand for thousands of kilometers. Particles from Saharan sand and dust storms can blow across islands in the Caribbean Sea and the U.

Dust storms in the tropics can be devastating for the local community. Valuable topsoil is blown away and visibility can drop to almost zero. Across the ocean, dust makes the sky hazy. These dust storms are often associated with dry, low-pressure areas and a lack of tropical storms.

Doldrums The place where trade winds of the two hemispheres meet is called the intertropical convergence zone ITCZ. The area around the ITCZ is called the doldrums. Prevailing winds in the doldrums are very weak, and the weather is unusually calm.

In fact, the low-pressure doldrums are created as the sun heats the equatorial region and causes air masses to rise and travel north and south. This warm, low-pressure equatorial wind descends again around the horse latitudes. Some equatorial air masses return to the doldrums as trade winds, while others circulate in the other direction as westerlies.

Although monsoons impact tropical as well as equatorial regions, the wind itself is created as the ITCZ moves slightly away from the Equator each season. This change in the doldrums disturbs the usual air pressure, creating the moisture-laden Southeast Asian monsoon. Results of Wind Wind traveling at different speeds, different altitudes, and over water or land can cause different types of patterns and storms. Jet Streams Jet stream s are geostrophic winds that form near the boundaries of air masses with different temperatures and humidity.

The rotation of the Earth and its uneven heating by the sun also contribute to the formation of high-altitude jet streams. These strong, fast winds in the upper atmosphere can blow kph mph. There is little turbulence in the stratosphere, which is why commercial airline pilots like to fly in this layer.

Riding with jet streams saves time and fuel. Have you ever heard someone talk about a headwind or tailwind when they are talking about airplanes?

These are jet streams. If they are behind the plane, pushing it forward, they are called tailwind s. They can help you get to your destination more quickly. If the winds are in front of the plane, pushing it back, they are called headwind s. Strong headwinds can cause flight delays. Hurricane A hurricane is a giant, spiraling tropical storm that can pack wind speeds of over kph mph and unleash more than 9 trillion liters 2.

These same tropical storms are known as hurricanes in the Atlantic Ocean, cyclone s in the northern Indian Ocean, and typhoon s in the western Pacific Ocean. These tropical storms have a spiral shape. The spiral swirling counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere develops as a high-pressure area twists around a low-pressure area. Wind conditions that can lead to hurricanes are called tropical disturbances. They begin in warm ocean waters when the surface temperatures are at least If the disturbance lasts for more than 24 hours and gets to speeds of 61 kph 38 mph , it becomes known as a tropical depression.

When a tropical depression speeds up to kph mph , it is known as a tropical storm, and is given a name. Meteorologist s name the storms in alphabetical order, and alternate with female and male names. When a storm reaches kph 74 mph , it becomes a hurricane and is rated from 1 to 5 in severity on the Saffir Simpson scale. A Category 5 hurricane is the strongest storm possible on the Saffir-Simpson scale.

Winds of a Category 5 blow at kph mph. Hurricane Ethel, the strongest hurricane in recorded history, roared across the Gulf of Mexico in September Winds were sustained at kph mph.

However, Hurricane Ethel quickly dissipate d. Although its winds ultimately blew as far north as the U. Hurricanes bring destruction to coastal ecosystems and communities. When a hurricane reaches land, it often produces waves that can reach 6 meters 20 feet high and be pushed by high winds kilometers miles inland.

These storm surge s are extremely dangerous and cause 90 percent of all hurricane deaths. The deadliest hurricane on record is the Great Hurricane of Although sophisticated meteorological equipment was not available at that time, winds may have reached kph mph as the hurricane hit Barbados and other islands in the Caribbean Sea.

This may have been enough to strip the bark from trees. More than 20, people died as a result of the hurricane as it made its way across Barbados, St. Although it decreased in intensity, the hurricane was tracked through the U.

Hurricanes can be destructive in other ways. High winds can create tornadoes. Heavy rains contribute to floods and landslides, which may occur many kilometers inland. Damage to homes, businesses, schools, hospitals, roads, and transportation systems can devastate communities and entire regions.

Hurricane Katrina, which blew through the Gulf of Mexico and into the southern U. New Orleans, Louisiana, was almost completely devastated by Hurricane Katrina. New Orleans, as well as Mobile, Alabama, and Gulfport, Mississippi, took years to recover from the damage done to their structures and infrastructure.

The best defense against a hurricane is an accurate forecast that gives people time to get out of its way. The National Hurricane Center issues hurricane watches for storms that may endanger communities, and hurricane warnings for storms that will reach land within 24 hours.

Cyclones Cyclones blow through the Indian Ocean in the same way hurricanes blow across the Atlantic. Cyclones blow in with air masses from the east, often the South China Sea, or the south. The most powerful and devastating cyclone in recorded history was the Bhola Cyclone.

Its winds were about kph mph as it made landfall along the coast of the Bay of Bengal, in what is today Bangladesh. More than , people died, and more than a million were made homeless.

Cyclone winds devastated fishing villages, and storm surges drowned crops. Typhoon Typhoons are tropical storms that develop over the northwest Pacific Ocean. Their formation is identical to hurricanes and cyclones. Typhoons form as equatorial winds and blow westward before turning north and merging with westerlies around the mid-latitudes.

Typhoons can impact a wide area of the eastern Pacific. The islands of the Philippines, China, Vietnam, and Japan are the most affected. However, typhoons have also been recorded as far as the U. Typhoons are often associated with extremely heavy rainfall. The wettest typhoon ever recorded was Typhoon Morakot in Morakot devastated the entire island of Taiwan, with winds of about kph 85 mph.

Storm surges and floods caused by those winds, however, caused the most damage. It blows from the northeast along the East Coast of the U. The U. Weather Service calls a storm a blizzard when the storm has wind speeds of more than 56 kph 35 mph and low visibility. Visibility is the distance that a person can see—blizzards, like fog, make visibility difficult and a task like driving dangerous.

The storm must go on for a prolonged period of time to be classified as a blizzard, usually a few hours. Blizzards can isolate and paralyze areas for days, especially if the area rarely has snowfall and does not have the equipment to clear it from the streets. The Great Blizzard of was perhaps the worst in U. More than centimeters 58 inches of snow fell across the region, causing freezing temperatures and massive flooding as the snow melted.

Monsoon A monsoon is a seasonal change in the prevailing wind system of an area. They always blow from cold, high-pressure regions. Monsoons are part of a yearlong cycle of uneven heating and cooling of tropical and mid-latitude coastal regions.

Monsoons are part of the climate of Australia, Southeast Asia, and in the southwestern region of North America. The air over land is heated and cooled more quickly than the air over the ocean. During summer, this means warm land-air rises, creating a space for the cool and moist air from the ocean. As the land heats the moist air, it rises, cools, condenses, and falls back to Earth as rain.

During the winter, land cools more quickly than the ocean. The warm air over the ocean rises, allowing cool land-air to flow in. Most winter monsoons are cool and dry, while summer monsoons are warm and moist. The famous summer monsoon, on the other hand, develops over the Indian Ocean, absorbing tremendous amounts of moisture. The summer monsoon is essential for the health and economies of the Indian subcontinent.

Aquifers are filled, allowing water for drinking, hygiene , industry , and irrigation. Tornado A tornado , also called a twister, is a violently rotating funnel of air. Tornadoes can occur individually or in multiples, as two spinning vortex es of air rotating around each other. Tornadoes can occur as waterspout s or landspouts, spinning from hundreds of meters in the air to connect the land or water with clouds above.

Although destructive tornadoes can occur at any time of day, most of them occur between 4 and 9 p. Tornadoes often occur during intense thunderstorms called supercells. A supercell is a thunderstorm with a powerful, rotating updraft. A draft is simply a vertical movement of air. This powerful updraft is called a mesocyclone. A mesocyclone contains rotating drafts of air 1 to 10 kilometers 1 to 6 miles in the atmosphere.

When rainfall increases in the supercell, rain can drag the mesocyclones down with it to the ground. This downdraft is a tornado. Depending on the temperature and moisture of the air, a tornado can last a few minutes or over an hour.

However, cool winds called rear flank downdrafts eventually wrap around the tornado and cut off the supply of warm air that feeds it. Most tornadoes have wind speeds of less than kph mph , and are about 76 meters feet across. They can travel for several kilometers before dissipating. However, the most powerful tornadoes can have wind speeds of more than kph mph and be more than 3 kilometers 2 miles across.

These tornadoes can travel across the ground for dozens of kilometers and through several states. These violent storms occur around the world, but the United States is a major hotspot with about a thousand tornadoes every year. The most extreme tornado ever recorded occurred on March 18, The tornado destroyed local communications, making warnings for the next town nearly impossible.

The Tri-State Tornado killed people in 3. The best protection against a tornado is early warning. In areas where tornadoes are common, many communities have tornado warning systems. In Minnesota, for example, tall towers throughout neighborhoods sound an alarm if a tornado is near.

Measuring Winds Wind is often measured in terms of wind shear. Wind shear is a difference in wind speed and direction over a set distance in the atmosphere.

Wind shear is measured both horizontally and vertically. Wind shear is measured in meters per second times kilometers of height. Under normal conditions, the winds move much faster higher in the atmosphere, creating high wind shear in high altitudes.

Wind shear is higher near the coast, for example. The amount of force that wind is generating is measured according to the Beaufort scale. The scale is named for Sir Francis Beaufort, who established a system for describing wind force in for the British Royal Navy. The Beaufort scale has 17 levels of wind force. An anemometer is a device for measuring wind speed. Anemometers are used with tornado data collectors, which measure the velocity , precipitation, and pressure of tornadoes. The scale has six categories that designate increasing damage.

In , the Enhanced Fujita Scale was established in the U. The Enhanced Fujita Scale has 28 categories, with the strongest cataloging damage to hardwood and softwood trees. Hurricanes are measured using the Saffir-Simpson scale. In addition to tropical depressions and tropical storms, there are five categories of hurricanes. The most powerful, Category 5, is measured by winds whipping at kph mph.