Westerlies are generally strongest in the winter hemisphere and at times when the pressure is lower over the poles. Furthermore, they are weakest in the summer hemisphere and when pressures are higher over the poles.
Westerlies are particularly strong, especially in the southern hemisphere, where there is less land in the middle latitudes to cause the flow pattern to amplify or become more north-south oriented. The strongest westerly winds in the middle latitudes can come in the Roaring Forties which is between 40 and 50 degrees latitude. This creates what is known as the Polar Hadley cell or Polar cell.
The video from Keith Meldahl [5] below illustrates each of the described winds, along with a visualization of each. Fossil Fuels. Nuclear Fuels. Acid Rain. Climate Change. Climate Feedback. Ocean Acidification. They tend to blow from the high pressure area in the horse latitudes towards the poles. Your comments may be used on air. Be polite. Inappropriate posts or posts containing offsite links, images, GIFs, inappropriate language, or memes may be removed by the moderator.
Learn More. Lehigh Valley News. This is a low-pressure system. This is a high-pressure system. 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.
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