Why do winds occur

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. Wind is a part of weather we experience all the time, but why does it actually happen? The air will be still one day, and the next, powerful gusts of wind can knock down trees.

What is going on here? The main cause of wind is a little surprising. The gases that make up our atmosphere do interesting things as the temperatures change.

When gases warm up, the atoms and molecules move faster, spread out, and rise. When air is colder, the gases get slower and closer together. Along this temperature boundary, a fierce atmospheric battleground develops. Colliding air masses of different temperatures spin up cyclones and other severe weather. The position of the jet stream influences the type of weather a region encounters. Consider the Northern Hemisphere, for instance. This allows an extensive dome of super-cold air to bank up nearby.

Atmospheric scientists refer to this flowing pool of cold air and low pressure as the polar vortex. It swells in size during winter. And when this flow of cold air surges southward, it pushes the jet stream into southern Canada and the northern United States. That can bring seemingly endless snowstorms to the upper Midwest and Northeast during the dead of winter.

In summer, the poles warm. This weakens the temperature gradient between these zones and the equator. The jet stream responds by retreating some 1, kilometers a thousand miles northward. Now, the weather in the lower 48 U. Sure, scattered thunderstorms erupt from time to time. But there are no huge storm systems spanning 1, kilometers or more to influence day-to-day events. Ordinarily, air would flow from high pressure to low pressure. It would move across a pressure gradient. So the driving force would be known as the pressure gradient force.

But the Coriolis force is still at play. These two forces cancel out. It just meanders slowly around large pressure systems. As a result, the air ends up circling around high- or low-pressure systems without moving toward or away from them. Closer to the surface, the flow is slightly ageostrophic meaning the winds are no longer in complete balance , due to the effects of friction with things at or near the surface.

Sometimes, however, a low-pressure system spins so fast that a third force develops. This is centrifugal force. Furthermore, buoyancy itself is reduced by turbulent mixing between air inside and outside the cloud, a process that is difficult to model Heus et al.

Friction forces are typically assumed to be strong for small drafts in convection, but cannot directly be measured, and could be small in some circumstances. The degree of mixing and friction significantly affect the maximum height calculated for situations of apparent convective instability Figure 3. Recent work suggests that pressure-gradient forces independent of buoyancy may explain why the strongest storms are mostly restricted to continents and large islands rather than over oceans.

During the day, heating near a coast warms the air above; this air then rises as part of a sea breeze circulation, with cooler marine air intruding over the land Figure 4. The most severe convection seems to occur when opposing breezes or waves collide in the afternoon the time of maximum convective instability. Figure 4 Development of convection in response to the solar-induced sea breeze. Heating of the ground drives shallow convection and is spread upward first panel ; this air rises and spreads out while marine air flows in near the ground, the head of this current triggering some cloud deepening second panel ; strong storms can occur when fronts collide, especially in the afternoon when the ground is warmest third panel.

Further research should continue to unravel the secrets of what controls the outbreak and character of cloud systems, in the Tropics and beyond. Progress in this area is crucial for continued improvement in weather- and climate-forecasting accuracy. Until then, important phenomena ranging from tomorrow's thunderstorms to next season's rainfall totals, although not as hard to predict as the mercurial behavior of the gods, will often continue to surprise us.

Heus, T. Mixing in shallow cumulus clouds studied by Lagrangian particle tracking. Journal of the Atmospheric Sciences 65 , Robinson, F. Exploring the land-ocean contrast in convective vigor using islands. Journal of the Atmospheric Sciences 68 , Zipser, E. The vertical profile of radar reflectivity of convective cells a strong indicator of storm intensity and lightning probability?

Monthly Weather Review , Modeling Sea Level Rise. The Global Climate System. Earth's Earliest Climate. Methane Hydrates and Contemporary Climate Change. Where Do Winds Come From? Citation: Sherwood, S. Nature Education Knowledge 4 2 How winds finally end up blowing the way they do results from a fascinating interplay of different forces, each acting on different length and time scales. Aa Aa Aa. Figure 1.

A geostrophically balanced wind cone-headed arrow aloft e. Figure 2.