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Jet streams are among the most powerful and influential atmospheric phenomena on Earth, shaping weather patterns, driving climate systems, and affecting everything from daily temperatures to extreme weather events. These fast-flowing, narrow air currents found in the upper levels of the atmosphere play a crucial role in the global circulation of air and energy. Understanding the formation and function of jet streams is essential not only for meteorologists and climate scientists but also for educators, students, aviation professionals, and anyone interested in how our planet’s atmospheric systems work.
This comprehensive guide explores the intricate mechanisms behind jet stream formation, their various types, their profound influence on weather and climate, and the emerging research on how climate change is affecting these critical atmospheric rivers. From the basic physics that creates these high-altitude winds to their role in extreme weather events, we’ll examine every aspect of these fascinating atmospheric features.
What Are Jet Streams?
Jet streams are types of air currents that form high in the atmosphere, creating narrow bands of exceptionally strong winds that encircle the globe. These relatively narrow bands of strong wind typically occur around 30,000 feet (9,100 meters) in elevation, though their exact altitude varies depending on the type of jet stream and geographic location.
Jet streams are thousands of kilometers in length and hundreds of kilometers in width, with wind speeds in the core often higher than 100 knots and occasionally exceeding 200 knots. To put this in perspective, jet streams move at about 110 miles per hour on average, but dramatic temperature differences between warm and cool air masses can cause them to reach speeds of 250 miles per hour or faster.
Within jet streams, the winds blow from west to east, but the band often shifts north and south because jet streams follow the boundaries between hot and cold air. Rather than being simple, straight-flowing rivers of air, jet streams meander across the planet in wave-like patterns, creating the complex weather systems we experience at the surface.
On Earth there are four main jet streams: two polar jet streams and two subtropical jet streams, which form in the atmosphere where warm air masses meet cool air masses. These jet streams exist in both the Northern and Southern Hemispheres, creating a global network of high-altitude wind currents that profoundly influence our planet’s weather and climate systems.
The Physical Mechanisms Behind Jet Stream Formation
The formation of jet streams results from a complex interplay of several fundamental atmospheric processes. Understanding these mechanisms provides insight into why these powerful wind currents exist and how they behave.
Temperature Gradients: The Primary Driver
The Sun doesn’t heat the whole Earth evenly, which is why areas near the equator are hot and areas near the poles are cold. When Earth’s warmer air masses meet cooler air masses, the warmer air rises up higher in the atmosphere while cooler air sinks down to replace the warm air, creating an air current or wind.
Jet streams are created where there are significant temperature differences between air masses, such as between warm tropical air and cold polar air. The strongest temperature gradient occurs along the polar frontal zone, and this rapid change of temperature with distance causes a rapid pressure change due to the thermal wind effect (a vertical shear in the geostrophic wind caused by a horizontal temperature gradient), creating the strong pressure gradient across the polar front that causes intense wind speeds.
The relationship between temperature gradients and jet stream strength is particularly evident in seasonal variations. The temperature contrast between north and south along the polar front is more intense during the winter than during the summer, so the polar jet is also stronger during the winter. This explains why winter weather patterns tend to be more dynamic and severe than summer patterns in mid-latitude regions.
The Coriolis Effect and Earth’s Rotation
The polar and subtropical jet streams are the product of two factors: the atmospheric heating by solar radiation that produces the large-scale polar, Ferrel, and Hadley circulation cells, and the action of the Coriolis force acting on those moving masses, which is caused by the planet’s rotation on its axis.
The rotational speed of the Earth’s surface, and thus the air above it, is relative to its latitude. Since the entire Earth makes one rotation in 24 hours, locations along the longer latitudes are rotating at a faster speed than the shorter ones because they are traveling more distance in the same amount of time. Therefore, the Earth’s rotational speed is fastest at its widest point, the equator.
As a result, air moving away from the equator does not move directly north and south because it retains this rotational momentum, causing it to rotate faster than the surface below as it moves toward the poles. This deflection of moving air masses is what creates the characteristic west-to-east flow of jet streams.
The Coriolis effect is also responsible for the specific latitudes where jet streams form. Because the Earth is rotating from west to east, the path of a moving air parcel bends to the right (this Coriolis force is also why hurricanes and other storms rotate counterclockwise in the Northern Hemisphere). Around 30° north and south of the equator, the Coriolis force is strong enough to bend the air flow so it’s west-east, and the air traveling northward in the Hadley cell gradually turns toward the east, speeding up as it goes.
Atmospheric Pressure Systems
High and low-pressure systems in the atmosphere can enhance the strength of jet streams. The interaction between pressure gradients and temperature differences creates the conditions necessary for jet stream formation and maintenance. The actual appearance of jet streams results from complex interaction between many variables, such as the locations of high and low pressure systems, warm and cold air, and seasonal changes. They meander around the globe, dipping and rising in altitude/latitude, splitting at times and forming eddies, and even disappearing altogether to reappear somewhere else.
The relationship between jet streams and surface pressure systems is bidirectional. While pressure systems influence jet stream behavior, the jet streams themselves help create and steer surface weather systems, including areas of high and low pressure that bring different weather conditions to various regions.
Types of Jet Streams and Their Characteristics
Not all jet streams are created equal. Different types of jet streams exist at various latitudes and altitudes, each with distinct characteristics and impacts on weather patterns.
Polar Jet Streams
The polar jet is located between the 50°-60° latitude lines in both the northern and southern hemispheres. The polar jet stream forms near the interface of the polar and Ferrel circulation cells, and polar jet streams are typically located near the 250 hPa pressure level, or 30,000 ft above sea level. The polar jets, at lower altitude and often intruding into mid-latitudes, strongly affect weather and aviation.
The polar jet stream is located near the polar front about 10 km up, near 50° to 60° latitude. These jet streams are particularly important for weather forecasting because they directly influence the movement of storm systems and temperature patterns across populated mid-latitude regions.
The polar jet is extremely variable, meanders extensively north and south, is about 5° latitude wide, and has widely varying speeds (25 to 100 m s–1) driven by varying horizontal temperature gradients. This variability makes the polar jet stream both fascinating and challenging for meteorologists to predict.
The polar jet stream’s position and strength change with the seasons. During winter, the leading edge of the cold polar air pushes further south into subtropical areas. During the summer, the polar front retreats into higher latitudes and is weakened. By summer in the Northern Hemisphere, the polar jet is typically found near the U.S.-Canadian border, and as autumn approaches and the Sun’s elevation decreases, the jet stream’s average latitude moves toward the equator.
Subtropical Jet Streams
The subtropical jet is located around the 30° latitude line. The subtropical jet forms near the boundary of the Ferrel and Hadley circulation cells, and subtropical jet streams are somewhat higher than polar jets.
The subtropical jet stream is located near 30° latitude about 13 km up, above the tropical high, and tends to form just above the descending branch of the Hadley cell, at about 12 km altitude. Here, a boundary exists between warmer equatorial air and cooler air that has been cycled up and around the Ferrel cell from the polar front. This is sometimes referred to as the subtropical front, but it does not extend all the way to the surface. The temperature gradient is strongest aloft near the tropopause, which induces a sharp pressure gradient and strong winds aloft as well.
Actual typical wind speeds in the subtropical jet are of order 40 to 80 m s–1 in the winter hemisphere, and slower in the summer hemisphere. While generally weaker than polar jets, subtropical jet streams play important roles in transporting moisture and heat from tropical regions and can significantly influence weather patterns when they interact with polar jets.
The subtropical jet is stronger over the western Pacific region, on average, than any other place in the world, with average speeds near Japan exceeding 70 meters per second (about 157 miles per hour) during meteorological winter. This regional variation in subtropical jet strength has important implications for weather patterns across Asia and the Pacific.
Jet Stream Interactions and Merging
The polar jet can sometimes merge with the subtropical jet if it sweeps southward enough, and it occasionally splits into two jet streams. The mid-latitude, polar, polar front, or eddy-driven jet usually merges with the subtropical jet during the winter over the North Pacific Ocean, especially during El Niño winters.
These interactions between different jet streams create complex atmospheric patterns that can lead to significant weather events. When jet streams merge, they can create particularly strong wind currents that enhance storm development and influence weather patterns over vast geographic areas.
Rossby Waves: The Meandering Nature of Jet Streams
One of the most important features of jet streams is their tendency to meander in large-scale wave patterns known as Rossby waves. Understanding these waves is crucial to comprehending how jet streams influence weather.
What Are Rossby Waves?
Rossby waves in the Earth’s atmosphere are easy to observe as (usually 4–6) large-scale meanders of the jet stream. When these deviations become very pronounced, masses of cold or warm air detach and become low-strength cyclones and anticyclones, respectively, and are responsible for day-to-day weather patterns at mid-latitudes.
Rossby waves are large horizontal atmospheric undulations associated with the polar-front jet stream that separate cold polar air from warm tropical air. These waves are named for Carl-Gustaf Arvid Rossby, who first identified them and explained their movement.
The meandering jet streams are called Rossby Waves, which are natural phenomena in the atmosphere and oceans due to rotation of earth. In planetary atmospheres, they are due to the variation in the Coriolis effect (when temperature contrast is low, speed of jet stream is low, and Coriolis force is weak leading to meandering) with latitude.
Formation and Characteristics of Rossby Waves
Rossby waves are formed when polar air moves toward the Equator while tropical air is moving poleward. Because of the temperature difference between the Equator and the poles due to differences in the amounts of solar radiation received, heat tends to flow from low to high latitudes; this is accomplished, in part, by these air movements.
Each large meander, or wave, within the jet stream is known as a Rossby wave (planetary wave), which are caused by changes in the Coriolis effect with latitude. These waves play a fundamental role in the global transport of heat and momentum from the tropics toward the poles.
Rossby waves help transfer heat from the tropics toward the poles and cold air toward the tropics in an attempt to return atmosphere to balance. They also help locate the jet stream and mark out the track of surface low pressure systems. This heat transport function is essential for maintaining Earth’s energy balance and preventing extreme temperature differences between equatorial and polar regions.
Rossby Waves and Weather Patterns
The existence of these waves explains the low-pressure cells (cyclones) and high-pressure cells (anticyclones) that are important in producing the weather of the middle and higher latitudes. The wave-like pattern of jet streams creates alternating regions of divergence and convergence in the upper atmosphere, which in turn influences the development of surface weather systems.
Jet streams have a strong influence on local weather because mid-latitude cyclones (surface Lows and their fronts and bad weather) are created on the east side of jet-stream troughs (about halfway between the trough axis and the ridge). Weather forecasters often use the location of the jet streams and their troughs and ridges to predict weather.
The amplitude and wavelength of Rossby waves determine the severity and persistence of weather patterns. More waviness in the jet stream means that rain and wind remain in a region longer than if the jet stream simply traveled due east with no detours. This can lead to prolonged periods of extreme weather, including extended heat waves, droughts, or flooding events.
The Role of Jet Streams in Weather Systems
Jet streams are fundamental drivers of weather patterns across the globe, influencing everything from daily temperature fluctuations to the development of severe storms.
Storm Development and Guidance
The jet stream is a band of enhanced westerly winds in the middle and upper troposphere found in both hemispheres. It steers large-scale weather systems and influences daily to weekly weather patterns with its meanderings. Mid-latitude weather is characterized by extratropical cyclones (ETCs), which are organized into storm tracks on climatological timescales. Another prominent atmospheric feature in the mid-latitudes is the eddy-driven jet stream, which acts as a guide for ETCs. It is critical to study the storm track and the jet stream together, as they are closely connected.
Jet streams can enhance the development of storms by providing lift and creating instability in the atmosphere. The divergence of air in the upper levels of the atmosphere, particularly on the eastern side of jet stream troughs, creates a vacuum effect that draws air upward from the surface. This rising motion is essential for storm development and intensification.
The fast-moving air currents in a jet stream can transport weather systems across the United States, affecting temperature and precipitation. However, if a weather system is far away from a jet stream, it might stay in one place, causing heat waves or floods. This relationship between jet stream position and weather system movement is crucial for understanding both typical weather patterns and extreme events.
Temperature Distribution and Fluctuations
Jet streams help transport warm and cold air across different regions, leading to significant temperature changes. The meandering pattern of jet streams creates a complex distribution of temperature across mid-latitude regions. When a jet stream dips southward (forming a trough), it can bring cold polar air far south of its typical range. Conversely, when it bulges northward (forming a ridge), warm tropical air can reach unusually high latitudes.
Jet streams can move in different ways, creating bulges of winds to the north and south. Storms tend to follow the edge of the jet stream, where the difference between cool and warm air creates the turbulent conditions for storms. This boundary between air masses is where the most dramatic weather often occurs.
The position of the jet stream relative to a location determines whether that area experiences warmer or cooler than average temperatures. Regions on the cold side of the jet stream typically experience below-average temperatures, while those on the warm side see above-average temperatures. Shifts in jet stream position can therefore cause rapid and significant temperature changes.
Precipitation Patterns and Distribution
Jet streams influence where and when precipitation occurs by guiding moisture-laden air and steering storm systems. The interaction between jet streams and surface weather systems determines precipitation patterns across large geographic areas. Areas located beneath the jet stream, particularly on the eastern side of troughs, often experience enhanced precipitation due to the lifting motion and convergence of moisture.
El Niño is a weather pattern whose conditions push the jet stream south, at times as far as the Gulf of America. During El Niño conditions, the eastern Pacific Ocean near the equator warms up. When the water warms up, the air above it also warms, creating far-reaching weather changes. These changes in jet stream position during El Niño events can dramatically alter precipitation patterns, bringing increased rainfall to some regions while causing drought in others.
The relationship between jet streams and precipitation is complex and varies by season and region. Understanding this relationship is essential for seasonal forecasting and water resource management, particularly in regions that depend on predictable precipitation patterns for agriculture and water supply.
Jet Streams and Climate Systems
Beyond their day-to-day influence on weather, jet streams play a significant role in shaping long-term climate patterns and regional climates around the world.
Defining Climate Zones
Jet streams help define climate zones by influencing temperature and precipitation patterns over extended periods. The average position of jet streams determines which regions receive more or less precipitation and whether they experience predominantly warm or cool conditions. Areas that frequently lie beneath the jet stream tend to have more variable weather and higher precipitation, while regions consistently on one side or the other of the jet stream experience more stable climate conditions.
The seasonal migration of jet streams is a key factor in creating distinct climate zones. As jet streams shift poleward in summer and equatorward in winter, they bring different weather regimes to various regions, contributing to the seasonal climate patterns that characterize different parts of the world.
Seasonal Variations and Climate Patterns
The position and strength of jet streams shift with the seasons, affecting seasonal weather changes. Jet streams also “follow the Sun” – as the Sun’s elevation increases each day in the spring, the average latitude of the jet stream shifts poleward. This seasonal migration is a fundamental driver of the changing weather patterns we experience throughout the year.
During winter the poles are colder relative to the equator, driving faster jet-stream winds than summer. Peak winds in the jet core can reach 100 m s–1, although 3-month-average speeds are typically 40 m s–1. This seasonal variation in jet stream strength has important implications for winter storm intensity and the severity of cold air outbreaks.
Teleconnections and Global Climate Patterns
Ocean-atmosphere coupling is most powerful in the tropics, where the coupling is responsible for the well-known “El Niño-Southern Oscillation” in the equatorial Pacific Ocean. The El Niño-Southern Oscillation, in turn, remotely leads to a meandering jet stream in the mid-latitudes through the formation of large-scale atmospheric circulation patterns, i.e., teleconnection patterns.
Extratropical ocean-atmosphere coupling enhances teleconnection patterns and causes more meandering westerly jet streams, which are linked to extreme weather events. These teleconnections allow climate variations in one part of the world to influence weather patterns thousands of miles away, demonstrating the interconnected nature of Earth’s climate system.
Understanding these teleconnections is crucial for seasonal forecasting and climate prediction. By monitoring conditions in key regions like the tropical Pacific, meteorologists can make informed predictions about likely jet stream behavior and associated weather patterns in distant locations.
Monitoring and Forecasting Jet Streams
Accurate monitoring of jet streams is essential for weather forecasting, aviation safety, and climate research. Modern technology has provided meteorologists with powerful tools to track and predict jet stream behavior.
Weather Satellites and Remote Sensing
Weather satellites provide real-time data on jet stream positions and speeds from space. These satellites use various instruments to measure atmospheric temperature, moisture, and wind patterns at different altitudes. By tracking cloud movements and temperature gradients, satellites can identify jet stream locations and monitor their evolution over time.
Satellite observations are particularly valuable because they provide continuous, global coverage of the atmosphere. This allows meteorologists to track jet streams over oceans and remote regions where ground-based observations are sparse or nonexistent. The data from satellites is integrated into weather forecasting models to improve predictions of jet stream behavior and associated weather patterns.
Weather Balloons and Upper-Air Observations
Weather balloons collect data on temperature, humidity, and wind patterns at various altitudes, providing crucial information about atmospheric conditions in the upper troposphere where jet streams reside. These balloons, also known as radiosondes, are launched twice daily from hundreds of locations around the world, ascending to altitudes of 30 kilometers or more.
As the balloons rise through the atmosphere, they transmit measurements back to ground stations, creating vertical profiles of atmospheric conditions. This data is essential for identifying the exact altitude, strength, and structure of jet streams. The information from weather balloons complements satellite observations and provides ground truth for validating satellite measurements and computer models.
Computer Models and Numerical Weather Prediction
Advanced computer models simulate atmospheric conditions to predict jet stream behavior. These numerical weather prediction models solve complex mathematical equations that describe atmospheric physics, incorporating data from satellites, weather balloons, surface observations, and aircraft reports. The models can forecast jet stream positions, strength, and evolution days to weeks in advance.
Modern forecasting models have become increasingly sophisticated, with higher resolution and better representation of atmospheric processes. However, predicting jet stream behavior remains challenging due to the chaotic nature of the atmosphere and the complex interactions between different atmospheric phenomena. Ensemble forecasting, which runs multiple model simulations with slightly different initial conditions, helps quantify uncertainty in jet stream predictions.
Jet Streams and Aviation
Jet streams have profound implications for aviation, affecting flight times, fuel consumption, and passenger comfort.
Flight Planning and Fuel Efficiency
The location of the jet stream is important for aviation. Aircraft flight time can be dramatically affected by either flying with the flow or against it. Often, airlines work to fly with the jet stream to obtain significant fuel cost and time savings.
Commercial use of the jet stream began on 18 November 1952, when Pan Am flew from Tokyo to Honolulu at an altitude of 7,600 metres. It cut the trip time by over one-third, from 18 to 11.5 hours. Within North America, the time needed to fly east across the continent can be decreased by about 30 minutes if an airplane can fly with the jet stream.
Modern flight planning software incorporates jet stream forecasts to optimize flight routes. Pilots and dispatchers work together to find routes that maximize tailwinds when flying eastward or minimize headwinds when flying westward. This optimization can result in significant fuel savings and reduced flight times, benefiting both airlines and passengers.
Turbulence and Passenger Safety
While jet streams can provide beneficial tailwinds, they can also create challenging flying conditions. The strong wind shear associated with jet streams—the rapid change in wind speed and direction over a short distance—can cause clear-air turbulence, which is turbulence that occurs in cloudless skies and cannot be detected visually.
Clear-air turbulence near jet streams is a significant concern for aviation safety and passenger comfort. Pilots use weather forecasts and real-time reports from other aircraft to avoid areas of severe turbulence when possible. However, unexpected encounters with turbulence remain a hazard, particularly as climate change may be affecting jet stream behavior and turbulence patterns.
Climate Change and Jet Stream Behavior
As Earth’s climate continues to warm due to increasing greenhouse gas concentrations, scientists are observing and predicting significant changes in jet stream behavior. Understanding these changes is crucial for anticipating future weather patterns and climate impacts.
Observed Changes in Jet Stream Position
Climate models predict a weak poleward shift of the jets in response to continuing climate change. Evidence shows that general poleward shifts are emerging, though the significance of these trends is often low and varies between datasets, but the similarity across different seasons and hemispheres is notable.
A recent paper by Keel et al (2024) showed that the wintertime North Pacific jet stream has shifted northwards since the beginning of the satellite-era in 1979. This northward shift likely contributed to the drying trend which made the January 2025 wildfires in Los Angeles more likely. This example demonstrates how jet stream changes can have direct and severe impacts on regional weather and climate hazards.
As the globe continues to warm, it is already having an effect on the jet stream and corresponding weather patterns, according to the latest U.N. IPCC climate report, which states: “It is likely that circulation features have moved poleward since the 1970s, involving a widening of the tropical belt, a poleward shift of storm tracks and jet streams, and a contraction of the northern polar vortex.
Arctic Amplification and Jet Stream Waviness
One of the most discussed aspects of climate change’s impact on jet streams is the phenomenon of Arctic amplification—the observation that the Arctic is warming faster than the rest of the planet. With the Arctic warming three times faster than the average for rest of the world, the temperature difference between North and South decreases and so does the speed of the jet stream’s westerly winds. As these winds slow down, its waves typically grow bigger and extend farther to the North and the South. Larger jet-stream waves move eastward more slowly, affecting weather patterns across North America to Central Europe and Asia.
The big swings of the jet stream tend to be very persistent and to stay in the same place for a long time. As each wave brings either warm or cold air to a region, this slow movement can cause extreme weather patterns, such as heat waves, floods, cold spells, storms and droughts – and we are seeing these wavey patterns happen more frequently.
Examining weather data from 1979 to 2022, researchers found that as snow cover in northern Canada declined, the jet stream grew wavier, allowing warm air to settle over Greenland, hastening ice melt. One impact of the disproportionate warming at high latitudes, particularly in the arctic, that has occurred with climate change could be the jet stream and its westerly flow slowing down, causing stuck weather patterns that produce longer duration storms and longer lasting heat waves.
However, the relationship between Arctic amplification and jet stream behavior remains an active area of research with some uncertainty. While climate change is undeniably amplifying extreme winter weather, recent studies show that it is likely not doing so by making the jet stream wavier. Research shows that the jet stream isn’t doing anything unusual that would cause the recent increase in intense storms. Climate change is intensifying these storms through a different process.
Projected Changes in Jet Stream Speed
While some research has focused on jet stream position and waviness, other studies have examined how climate change will affect jet stream wind speeds. Research by UChicago Prof. Tiffany Shaw and National Center for Atmospheric Research scientist Osamu Miyawaki suggests that as the world warms, the fastest upper-level jet stream winds will get faster and faster—by about 2% for every degree Celsius the world warms. Furthermore, the fastest winds will speed up 2.5 times faster than the average wind.
Jet streams form because of the contrast between the cold, dense air at the poles and the warm, light air in the tropics, in combination with the rotation of the Earth. The new study uses climate models to show that climate change intensifies this density contrast because moisture levels for air above the tropics will increase more than above the poles.
This result is surprising because scientists previously thought that as the Arctic warmed faster than the middle latitudes, the weaker temperature gradient from equator to pole would result in a slower jet stream. But the new research shows that the gradient in water vapor content, which also affects the air’s density, will have a bigger effect, resulting in a stronger jet stream in the future.
Implications for Future Weather and Climate
Changes in jet stream behavior have significant implications for future weather patterns and extreme events. The faster the jet stream winds, the more severe the impacts on turbulence. The faster winds may also lead to conditions that are favorable for stronger and more prolonged storms.
While successive generations of climate model ensembles consistently project a mean poleward shift of the midlatitude zonal-mean maximum winds, there remains considerable intermodel spread and large uncertainty across seasonal and regional jet responses. Of particular note is our limited understanding of how these jets respond to the intricate interplay of multiple concurrent drivers, such as the strong warming in polar and tropical regions.
The uncertainty in jet stream projections poses challenges for regional climate adaptation planning. Changes in the eddy-driven jet stream as a response to climate change have the potential to strongly alter the hydroclimate of many extratropical regions. However, as highlighted, the response of the jet to increased greenhouse gases is uncertain, which poses a substantial challenge to providing reliable regional climate change projections. This uncertainty propagates to climate change impact studies and could render their outcomes of limited utility if the atmospheric circulation response is inadequately constrained.
Jet Streams and Extreme Weather Events
The connection between jet stream behavior and extreme weather events has become increasingly apparent in recent years, with numerous studies linking unusual jet stream patterns to devastating weather disasters.
Heat Waves and Persistent High Pressure
Scientists documented “extreme heatwaves” in Europe during the years 2003, 2010 and 2015. Each of those events has been linked to a series of Rossby waves that had meandered through the Northern Hemisphere’s subtropical jet stream. The twisting waves can stall high or low-pressure weather systems, restricting their movement for long periods. Under the wrong circumstances, that can trigger natural crises like floods and droughts.
A northward-shifted jet stream contributed to the extremely hot and dry European summer of 2022, while a weakened or shifted North Pacific jet stream reduces rainfall in California, increasing wildfire risk. These examples demonstrate how jet stream position and behavior can create conditions conducive to extreme heat and associated hazards.
Flooding and Prolonged Precipitation
Just as stalled jet stream patterns can cause heat waves, they can also lead to prolonged precipitation events and severe flooding. When a jet stream becomes locked in a particular pattern, moisture-laden storm systems can repeatedly affect the same regions, leading to cumulative rainfall totals that far exceed normal amounts.
While parts of the Arctic, including Svalbard and Northern Norway, recorded the warmest month and most summer days above 20 degrees Celsius, Central Europe saw devastating floods in later summer, impacting 2 million people on the continent. This illustrates how jet stream patterns can create contrasting extreme weather conditions in different regions simultaneously.
Cold Air Outbreaks and Winter Storms
Normally, the polar vortex has little influence on our weather, but every once in a while, it stretches into a bean shape, or it splits into two or three pockets. When that happens, those smaller pools of cold air can descend southward and reinforce a dip in the jet stream, making a cold spell much worse. This is exactly what happened in Texas in February 2021, when the U.S. state recorded the longest freezing streak in its history.
Large waves in the jet stream observed since the 1990s have, in recent years, driven abnormally frigid temperatures and devastating winter storms deep into regions such as the southern United States. These events demonstrate the jet stream’s role in bringing Arctic air to regions unaccustomed to such extreme cold, often with severe consequences for infrastructure and public safety.
Regional Variations in Jet Stream Behavior
Jet streams do not behave uniformly around the globe. Regional variations in geography, ocean temperatures, and atmospheric conditions create distinct jet stream characteristics in different parts of the world.
The North Atlantic Jet Stream
The response of the North Atlantic jet stream to a warmer climate shows considerable inter-model variability over Europe. In future climates, the jet stream shifts southward over the North Atlantic and extends further over Europe. Increasing sea surface temperatures drives these changes. The region of high activity of low-pressure systems is projected to move east towards Europe. Future increasing sea surface temperatures and sea ice loss contribute with similar magnitude to the eastward shift.
The North Atlantic jet stream is particularly important for European weather and climate. Its position and strength determine whether Europe experiences mild, wet winters or cold, dry conditions. Understanding how this jet stream will change in the future is crucial for European climate adaptation planning.
The North Pacific Jet Stream
The North Pacific jet stream exhibits unique characteristics influenced by the vast Pacific Ocean and the complex topography of Asia and North America. A recent paper by Keel et al (2024) showed that the wintertime North Pacific jet stream has shifted northwards since the beginning of the satellite-era in 1979.
This jet stream is strongly influenced by El Niño and La Niña events in the tropical Pacific. During El Niño winters, the subtropical and polar jets often merge over the eastern Pacific, creating a strong, extended jet that can bring increased storminess to the western United States. During La Niña, the jets tend to be more separated, often resulting in drier conditions in the southwestern United States.
The Southern Hemisphere Jet Stream
By combining calculation methods, researchers found that 50% of the observed shift in the Southern Hemisphere’s jet stream is directly attributable to global warming. The other half is caused by a combination of other climate-related changes.
Measurement data showed that the wind speeds in the Southern Hemisphere’s eddy-driven jet have increased while the wind belt has continually moved further toward the South Pole. The Southern Hemisphere jet stream is unique because it circles Antarctica with fewer land masses to disrupt its flow, creating a more zonally symmetric circulation pattern than in the Northern Hemisphere.
Advanced Topics in Jet Stream Science
Beyond the fundamental understanding of jet streams, several advanced topics are important for comprehensive knowledge of these atmospheric phenomena.
Jet Streaks and Localized Intensification
The jet stream is a hemisphere-wide midlatitude band of westerly wind. Jet streaks, which are regions of enhanced wind speed within the jet stream, characterize it locally. These jet streaks are areas where wind speeds are significantly higher than the surrounding jet stream, often exceeding 200 miles per hour.
Jet streaks are important for weather forecasting because they create regions of divergence and convergence that can trigger or intensify surface weather systems. The entrance and exit regions of jet streaks are associated with specific patterns of vertical motion that influence cloud formation, precipitation, and storm development.
Baroclinic Instability and Jet Stream Maintenance
Baroclinic instability is a fundamental process that helps maintain jet streams and generate mid-latitude weather systems. This instability arises from the horizontal temperature gradient in the atmosphere and the vertical wind shear associated with jet streams. When atmospheric conditions are favorable, small perturbations in the flow can grow through baroclinic instability, developing into the cyclones and anticyclones that characterize mid-latitude weather.
The interaction between baroclinic instability and jet streams creates a feedback loop: the temperature gradient maintains the jet stream through the thermal wind relationship, while the jet stream provides the wind shear necessary for baroclinic instability to develop. This process is essential for understanding how jet streams persist and how they interact with developing weather systems.
Stratospheric Influences on Jet Streams
While jet streams are primarily tropospheric phenomena, they can be influenced by conditions in the stratosphere above. The stratospheric polar vortex, a large-scale circulation pattern in the winter stratosphere, can affect the tropospheric jet stream below. When the polar vortex is strong and stable, the tropospheric jet stream tends to be more zonal (west-to-east). When the polar vortex weakens or becomes disrupted, the tropospheric jet stream often becomes more meridional (north-south), leading to more extreme weather patterns.
Sudden stratospheric warming events, during which the polar vortex rapidly weakens or splits, can have significant impacts on tropospheric weather patterns for weeks to months afterward. Understanding these stratosphere-troposphere interactions is an active area of research with important implications for extended-range weather forecasting.
Jet Streams on Other Planets
Jet streams are not unique to Earth. Jet streams have been detected in the atmospheres of Venus, Jupiter, Saturn, Uranus, and Neptune. Atmospheric Rossby waves, like Kelvin waves, can occur on any rotating planet with an atmosphere.
Studying jet streams on other planets provides valuable insights into the fundamental physics of atmospheric circulation. For example, Jupiter’s jet streams are much more numerous and persistent than Earth’s, with multiple jets at various latitudes that have remained stable for centuries. Saturn’s hexagonal cloud formation at its north pole is hypothesized to be related to Rossby waves and jet stream dynamics.
These planetary comparisons help scientists understand which aspects of jet stream behavior are universal consequences of atmospheric physics and which are specific to Earth’s particular conditions. This knowledge enhances our understanding of Earth’s jet streams and improves our ability to predict how they might change in the future.
The Future of Jet Stream Research
As climate change continues to impact global weather patterns, understanding jet streams becomes increasingly important. Several key areas of research are advancing our knowledge of these critical atmospheric features.
Improving Climate Models
The difficulty of simulating processes requiring high resolution, such as those linked to sharp sea surface temperature gradients or diabatic effects related to tropical convection and extratropical cyclones, has historically hindered progress. A collaborative effort is advocated to enhance our understanding of the jet stream response to climate change, proposing a series of new experiments that take advantage of recent advances in computing power and modelling capabilities to better resolve small-scale processes such as convective circulations, which are considered essential for a good representation of jet dynamics.
Higher-resolution climate models that can better represent jet stream dynamics and their interactions with other atmospheric processes are essential for improving regional climate projections. As computing power continues to increase, these more sophisticated models will provide better guidance for climate adaptation and mitigation strategies.
Enhanced Observational Networks
Continued monitoring and research are crucial for adapting to changes in jet stream behavior. Expanding observational networks, including additional weather balloon launches, improved satellite instruments, and aircraft-based measurements, will provide better data for understanding jet stream variability and trends.
New technologies, such as unmanned aerial vehicles capable of flying in the upper troposphere and advanced remote sensing instruments, may provide unprecedented observations of jet stream structure and evolution. These observations will be essential for validating and improving both weather forecasting and climate models.
Interdisciplinary Research Approaches
Understanding jet streams requires integrating knowledge from multiple disciplines, including atmospheric physics, oceanography, climate science, and data science. To understand what was driving the changes in the jet stream, researchers used a statistical framework called causal inference. This method helps to disentangle the distinct influence that individual climate drivers have even if they are closely linked. Using this approach, researchers were able to separate the various effects and quantify the specific role of each factor.
Interdisciplinary approaches that combine traditional meteorological analysis with advanced statistical methods, machine learning, and other innovative techniques are revealing new insights into jet stream behavior and its connections to other components of the climate system.
Practical Applications and Societal Relevance
Understanding jet streams has numerous practical applications that affect society, from weather forecasting to agriculture, water resource management, and disaster preparedness.
Seasonal Forecasting and Climate Services
Jet stream behavior is a key factor in seasonal weather forecasting. The jets can change from one week or month to the next and regional patterns of heat and cold, wet and dry will shift along with them. For much of the midlatitudes, the local jet stream is typically the single most important factor in regional weather variations on these timescales, so that if you only had one piece of information about the atmosphere, you would want to know about the jet.
Climate services that provide seasonal forecasts help various sectors plan for likely weather conditions months in advance. Agriculture, energy production, water management, and many other industries rely on these forecasts to make informed decisions. Improving our understanding of jet stream behavior enhances the accuracy and reliability of these critical forecasts.
Extreme Weather Preparedness
As jet stream patterns become potentially more erratic due to climate change, understanding their behavior becomes crucial for extreme weather preparedness. Communities can better prepare for heat waves, cold snaps, floods, and droughts when they understand the jet stream patterns that create these conditions.
Emergency management agencies, public health officials, and infrastructure planners all benefit from improved understanding of how jet streams influence extreme weather. This knowledge enables better early warning systems, more effective resource allocation, and more resilient infrastructure design.
Educational Importance
Educators and students alike can benefit from exploring the complexities of jet streams and their role in our environment. Understanding jet streams provides an excellent framework for learning about atmospheric physics, climate science, and the interconnected nature of Earth’s systems. The visual nature of jet stream patterns, readily observable in satellite imagery and weather maps, makes them an engaging topic for science education at all levels.
Teaching about jet streams also provides opportunities to discuss climate change, extreme weather, and the scientific process. Students can learn how scientists use observations, theory, and computer models to understand complex natural phenomena and make predictions about future conditions.
Conclusion
Jet streams are fundamental components of Earth’s atmospheric circulation, playing crucial roles in weather patterns, climate systems, and the global transport of energy and momentum. These fast-flowing rivers of air, formed by temperature gradients, Earth’s rotation, and atmospheric pressure systems, influence everything from daily weather to long-term climate patterns and extreme events.
The two main types of jet streams—polar and subtropical—each have distinct characteristics and impacts, but both are essential for understanding mid-latitude weather and climate. The meandering nature of jet streams, manifested in Rossby waves, creates the complex weather patterns we experience and enables the poleward transport of heat necessary for Earth’s energy balance.
As climate change continues to alter global temperature patterns, jet streams are responding in complex ways. While some aspects of these changes are becoming clearer—such as the general poleward shift of jet streams and the projected increase in maximum wind speeds—other aspects remain uncertain, including regional responses and the relationship between Arctic amplification and jet stream waviness. This uncertainty underscores the need for continued research, improved observations, and better climate models.
The practical importance of understanding jet streams cannot be overstated. From aviation safety and efficiency to seasonal weather forecasting, extreme weather preparedness, and climate adaptation planning, jet stream knowledge has wide-ranging applications that affect society. As we face a changing climate, this understanding becomes even more critical for anticipating and preparing for future weather and climate conditions.
For educators, students, meteorologists, climate scientists, and anyone interested in how our planet’s atmosphere works, jet streams offer a fascinating window into the complex dynamics of Earth’s climate system. By continuing to study these powerful atmospheric currents, we enhance our ability to predict weather, understand climate, and prepare for the challenges of a changing world.
For more information on atmospheric science and weather patterns, visit the National Oceanic and Atmospheric Administration or explore educational resources at NOAA SciJinks. To learn more about climate change impacts on atmospheric circulation, the Intergovernmental Panel on Climate Change provides comprehensive assessment reports. For real-time jet stream observations and forecasts, check out the Storm Prediction Center’s upper air maps. Those interested in the latest research can explore studies published in journals through Nature Climate Change.