Jet stream

Jet streams are fast, narrow air currents high up in the sky. They flow west to east around the globe and are found near the top of the atmosphere, close to a place called the tropopause. There are two main jet streams: the polar jet and the subtropical jet. The polar jet is stronger and flows around 30,000 feet above the Earth.

The northern polar jet moves over the middle to northern parts of North America, Europe, and Asia, while the southern polar jet circles around Antarctica.

Jet streams are important because they affect the weather. They influence weather patterns over the Pacific Ocean and can impact climates in many parts of the world. Meteorologists watch jet streams to help predict the weather. Airlines also use them to save time and fuel during flights.

Discovery

An American professor, Elias Loomis, first thought there might be strong winds high in the sky moving from west to east. After a big volcanic eruption in 1883, people saw how it changed the sky for years and called this the "equatorial smoke stream."

Later, a Japanese scientist named Wasaburo Oishi near Mount Fuji noticed these fast winds by watching special balloons called pilot balloons. An American pilot, Wiley Post, also helped discover jet streams when he flew around the world alone in 1933 and noticed his plane moving faster than expected.

A German scientist, Heinrich Seilkopf, gave jet streams their name in 1939. During World War II, pilots flying between places like the US and the UK, and over Guam, felt very strong tailwinds, which helped scientists learn more about these powerful air currents.

Description

Jet streams are fast, narrow currents of air high up in the sky. They form because of the sun's heat and the Earth's rotation. There are two main types: the polar jet stream and the subtropical jet stream. The polar jet stream is usually found near 30,000 feet above sea level, while the subtropical jet stream is a bit higher.

These jet streams flow from west to east around the world and can change the weather. They affect storms and can bring cold or warm air to different places. For example, in early 2026, very cold weather moved across North America because of the jet stream. Jet streams can twist and turn, creating patterns that help forecasters predict the weather.

Cause

See also: Extratropical cyclone and Thermal wind

Winds are strongest just below the tropopause. When two air masses with different temperatures meet, the air moves along the boundary between them because of pressure differences. This movement is changed by the Coriolis effect, which makes the wind flow along the edge of the two air masses.

The strong eastward jet streams happen partly because the Equator is warmer than the poles. As you go higher up, the wind moving east gets stronger. This is linked to how temperatures change from the Equator to the poles.

Polar jet stream

The polar jet stream forms partly because cold polar air pushes under warmer sub-tropical air at the polar front. This creates a sharp change in pressure, which helps form a tight, fast-moving jet stream at high altitudes.

Subtropical jet

The subtropical jet forms where the tropical Hadley cell ends. Warm air rises near the Equator, moves toward the poles, and then sinks. As it moves poleward, the Coriolis force pushes it eastward, creating a fast wind that flows from west to east.

Effects

Hurricane protection

The subtropical jet stream, which flows around a large upper-level trough in the ocean, helps protect the Hawaiian Islands from many hurricanes. For example, when Hurricane Flossie approached in 2007 but dissipated before reaching land, the U.S. National Oceanic and Atmospheric Administration said strong vertical wind changes were a key reason.

Uses

The northern polar jet stream is very important for aviation and weather forecasting. It is stronger and at a lower altitude than other jet streams and passes over many countries in the northern hemisphere. The southern polar jet stream mainly circles around Antarctica and sometimes the southern tip of South America.

Aviation

The jet stream’s location matters a lot for airplanes. Flying with the jet stream can save fuel and time, while flying against it can make trips longer. Airlines began using the jet stream for faster flights on November 18, 1952, when Pan Am flew from Tokyo to Honolulu in just 11.5 hours instead of 18.

In North America, flying with the jet stream can cut eastbound travel time by about 30 minutes. Over the Atlantic Ocean, the North Atlantic Tracks help airlines and air traffic control plan routes that use the jet stream safely.

Jet streams can sometimes cause sudden and strong turbulence.

Possible future power generation

See also: High-altitude wind power

Scientists are exploring ways to use the strong winds in the jet stream as a source of energy.

Unpowered aerial attack

Near the end of World War II, the Japanese used special fire balloons to travel across the Pacific Ocean using the jet stream. These were aimed at Canada and the United States.

Changes due to climate cycles

Effects of ENSO

Main article: Effects of the El Niño–Southern Oscillation in the United States

El Niño–Southern Oscillation (ENSO) changes the usual path of high-altitude winds called jet streams. This causes changes in rain and temperature across North America and affects storms in the Pacific and Atlantic oceans. Together with the Pacific Decadal Oscillation, ENSO can also influence rain in Europe during colder months. Changes in ENSO shift the jet stream's location over South America, affecting how rain is spread across the continent.

El Niño

During El Niño events, more rain is expected in California because storms follow a path further south. More rain falls along the Gulf coast and Southeast due to a stronger and more southerly jet stream. Snow is heavier than usual in the southern Rockies and Sierra Nevada mountains, but less snow falls in the Upper Midwest and Great Lakes area. The northern part of the United States stays warmer than normal in fall and winter, while the Gulf coast is cooler in winter. The jet stream in the northern hemisphere's tropics becomes stronger, which reduces storms in the Atlantic and increases them in the eastern Pacific. In the southern hemisphere, this jet stream moves north, preventing some storms and thunderstorms from reaching central parts of the continent.

La Niña

During La Niña in North America, more rain goes to the Pacific Northwest because storms and the jet stream move further north. This brings more snow to the Midwest and hotter, drier summers. The Pacific Northwest and western Great Lakes get more snow than usual. Over the North Atlantic, the jet stream is stronger, sending more rain and stronger weather systems to Europe.

Dust Bowl

Signs show that the jet stream played a role in the severe droughts of the 1930s Dust Bowl in the central United States. Usually, the jet stream moves east over the Gulf of Mexico and turns north, bringing moisture and rain to the Great Plains. But during the Dust Bowl, the jet stream weakened and took a path farther south than normal. This lack of rain caused extreme drought in the Great Plains and other parts of the Midwest.

Longer-term climatic changes

Since the early 2000s, scientists have looked at how a warming world changes jet streams. They found that global warming is slowly moving these fast air currents toward the poles. For example, between 1979 and 2001, the northern jet stream moved north by about 2 kilometres each year. Similar changes happened in the southern jet stream.

Some scientists think that as the Earth warms, jet streams might also become weaker. This idea relates to how the Arctic is heating up faster than other areas. As the temperature difference between the cold Arctic and warmer areas gets smaller, it could change the jet streams. This might lead to more extreme weather events, like heat waves or cold spells, in places farther from the poles. However, not all scientists agree, and more research is needed to fully understand these changes.

Other upper-level jets

Polar night jet

The polar-night jet stream forms in winter when nights are longer around 60° latitude. It flows at a higher altitude, about 24,000 metres, than in summer. During these dark months, the air over the poles gets colder than the air near the Equator. This temperature difference creates strong air pressure changes in the upper atmosphere. With Earth's rotation, these changes help form fast-moving polar night jets that travel eastward about 48 kilometres above the Earth. The polar night jet circles the polar vortex. Warmer air moves along the edge of the polar vortex but cannot enter it. Inside the vortex, the polar air stays cold because there is no warmer air from lower areas and little sunlight during the polar night.

Low-level jets

Fast winds near the ground are called jets. These winds are close to the Earth and help make weather patterns.

A barrier jet forms near mountains. It pushes the wind to flow alongside the mountains. In the North American Great Plains, a low-level jet helps make thunderstorms at night in warm months. In Australia, a jet pulls moisture from the Coral Sea toward the southwest.

Coastal jets happen where there is a big difference between hot land and cool sea temperatures. These jets create strong winds alongside the coast. They are common near places like California, Peru, and West Australia.

Valley exit jets are strong winds that flow out of valleys into flat areas. These winds can be very fast at some heights above the ground. They are often found in places with big mountain valleys, such as in the United States.

In Africa, low-level jets help move dust from the Sahara desert. One jet in Chad sends dust from the Bodélé Depression, a big source of dust in the world. The Somali Jet brings moisture to help with rains in Asia. Other jets in East Africa affect rainfall, bringing dry weather to some areas and wet weather to others like the Congo Basin.

Other planets

On other planets, jet streams are thought to be driven by internal heat instead of the sun. Jupiter has many jet streams in its atmosphere. These streams are created by convection cells powered by the planet’s internal heat, giving Jupiter its famous banded appearance.