Glossary

12.2 Jet streams and their influence on weather

4 min read•july 31, 2024

Jet streams, powerful winds high in the atmosphere, play a crucial role in shaping global weather patterns. These narrow bands of strong winds influence storm development, guide weather systems, and contribute to seasonal climate variations across different regions.

Understanding jet streams is key to grasping global circulation patterns. Their position and strength affect temperature distribution, precipitation, and extreme weather events. As climate change alters jet stream behavior, it may lead to more frequent and intense weather phenomena worldwide.

Jet streams and their formation

Characteristics and Dynamics

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  • Jet streams form narrow bands of strong winds in the upper troposphere and lower stratosphere at altitudes of 9-16 km (30,000-52,000 feet)
  • Wind speeds typically exceed 92 km/h (57 mph), reaching up to 400 km/h (250 mph) in extreme cases
  • Temperature gradient between equatorial and polar regions drives jet stream formation
  • Earth's rotation () influences jet stream patterns
  • relationship explains vertical structure with wind speed increasing with height in regions of strong horizontal
  • Jet streams form in segments extending thousands of kilometers, not continuous around the globe

Formation Mechanisms and Influences

  • Seasonal changes affect jet stream position and strength
  • Topography impacts jet stream patterns (mountain ranges)
  • Large-scale atmospheric circulation patterns influence jet stream behavior
  • Jet streams facilitate transfer of heat, moisture, and momentum across latitudes
  • Position and strength vary based on factors like solar radiation and surface temperature differences
  • Baroclinic instability contributes to jet stream development in mid-latitudes
  • Tropopause height variations play a role in jet stream formation and intensity

Polar vs Subtropical Jet Streams

Location and Characteristics

  • located at approximately 60° latitude in both hemispheres
  • found near 30° latitude
  • Polar jet generally stronger and more variable due to greater temperature contrasts
  • Polar jet associated with polar front, separating cold polar air masses from warmer mid-latitude air
  • Subtropical jet more stable and consistent in position
  • Polar jet exhibits significant seasonal variations, moving poleward in summer and equatorward in winter
  • Subtropical jet closely linked to Hadley cell circulation, most pronounced during winter months

Structural Variations and Behavior

  • Both jet streams can split, merge, or develop multiple branches
  • Complex flow patterns emerge in upper atmosphere due to jet stream interactions
  • Polar jet experiences more frequent meanders and undulations
  • Subtropical jet tends to be more zonal (west-to-east) in flow
  • Polar jet strength influenced by Arctic Oscillation and polar vortex behavior
  • Subtropical jet affected by tropical convection patterns and monsoon circulations
  • Jet stream interactions can lead to formation of hybrid or merged jet structures

Jet streams and weather systems

Influence on Storm Development and Movement

  • Jet streams act as steering currents for mid-latitude cyclones and anticyclones
  • Positioning enhances or suppresses vertical motion, affecting storm system development
  • Jet streaks (regions of maximum wind speed) associated with areas of divergence and convergence
  • Upper-level jet stream interaction with surface frontal systems can trigger severe weather (thunderstorms, tornadoes)
  • Jet streams create atmospheric , leading to persistent weather conditions
  • Meandering creates , crucial for large-scale weather pattern formation
  • Influence atmospheric moisture distribution, affecting precipitation patterns and extreme weather (droughts, floods)

Specific Weather Phenomena

  • Jet stream positioning impacts formation and intensity of extratropical cyclones
  • Polar jet stream interactions with cold air outbreaks can lead to severe winter storms
  • Subtropical jet stream influences development of tropical-extratropical transition events
  • Jet stream configurations contribute to atmospheric river events (narrow bands of concentrated moisture transport)
  • Jet stream patterns affect formation and movement of cut-off lows and upper-level troughs
  • Jet stream positioning influences development and track of nor'easters along eastern North America
  • Interaction between jet streams and mountain ranges can lead to lee cyclogenesis (development of low-pressure systems on leeward side of mountains)

Jet stream patterns and seasonal weather

Seasonal Variations and Regional Impacts

  • Jet stream position and strength exhibit significant seasonal variations, impacting regional climate patterns
  • Winter patterns feature equatorward shift and intensification of polar jet stream, leading to frequent, intense mid-latitude storms
  • Summer patterns show weaker, poleward-shifted jet stream, resulting in milder, more stable mid-latitude weather
  • Persistent configurations (omega blocks, cut-off lows) cause prolonged anomalous weather (heat waves, cold spells, extended rainfall)
  • El Niño and La Niña events significantly alter jet stream patterns, affecting global seasonal weather
  • Jet stream interactions with large-scale atmospheric oscillations (North Atlantic Oscillation, Pacific Decadal Oscillation) result in complex multi-year weather variations
  • Climate change potentially influences jet stream behavior, leading to more frequent extreme weather events
  • Observed changes in jet stream waviness and persistence linked to Arctic amplification
  • Potential shifts in regional climate patterns due to altered jet stream dynamics
  • Weakening of temperature gradient between equator and poles may affect jet stream strength and stability
  • Changes in jet stream patterns impact distribution of precipitation, leading to regional droughts or flooding events
  • Altered jet stream behavior potentially affects frequency and intensity of heat waves and cold air outbreaks
  • Long-term changes in jet stream characteristics may influence global atmospheric circulation patterns and teleconnections

Key Terms to Review (18)

Bernoulli's Principle: Bernoulli's Principle states that as the speed of a fluid increases, its pressure decreases, illustrating the relationship between fluid velocity and pressure. This principle plays a vital role in understanding atmospheric pressure and how it affects air movement, especially in high-altitude jet streams where variations in speed can create significant changes in pressure and influence weather patterns.
Blocking patterns: Blocking patterns are large-scale atmospheric configurations that impede the normal flow of the jet stream, causing persistent weather conditions in a particular region. These patterns often lead to prolonged periods of extreme weather, such as heat waves or cold snaps, by effectively 'blocking' the movement of air masses and associated weather systems. Understanding blocking patterns is essential for predicting significant weather events and their impacts on local climates.
Carl-Gustaf Rossby: Carl-Gustaf Rossby was a prominent Swedish meteorologist known for his pioneering work in atmospheric dynamics, particularly in the understanding of large-scale weather patterns and the influence of the Earth's rotation on atmospheric behavior. His research laid the foundation for understanding how temperature distribution, mid-latitude cyclone formation, and jet streams operate within the Earth's atmosphere, significantly impacting weather forecasting and climate studies.
Climate variability: Climate variability refers to the fluctuations in climate patterns that occur over different time scales, from months to decades, and can result from both natural processes and human influences. Understanding climate variability is essential for assessing long-term climate trends and recognizing how factors like atmospheric circulation, ocean currents, and human activity can influence weather patterns and climate conditions.
Coriolis effect: The Coriolis effect is the apparent deflection of moving objects, such as air or water, due to the rotation of the Earth. This phenomenon influences global wind patterns, storm systems, and ocean currents, leading to the characteristic rotation of weather systems and variations in local wind behavior.
Geostrophic balance: Geostrophic balance refers to the condition in which the horizontal pressure gradient force is exactly balanced by the Coriolis effect, resulting in winds that flow parallel to isobars rather than across them. This balance is critical for understanding large-scale wind patterns in the atmosphere, as it plays a significant role in shaping jet streams and influences weather systems. The concept helps meteorologists predict how air masses will move based on variations in atmospheric pressure and the Earth's rotation.
Jet stream dip: A jet stream dip refers to a significant southward deflection in the jet stream, which can influence weather patterns by allowing cold polar air to move into lower latitudes while warmer air from the tropics moves northward. This interaction can lead to extreme weather events, such as storms or unseasonably cold temperatures, impacting local climates and weather systems.
John Dalton: John Dalton was an English chemist and physicist best known for his pioneering work in the field of atomic theory in the early 19th century. His contributions laid foundational principles that not only advanced chemistry but also had significant implications for understanding atmospheric composition, weather phenomena, and various processes in meteorology.
Polar jet stream: The polar jet stream is a fast-flowing river of air located in the upper levels of the atmosphere, typically between 30° and 60° latitude, that significantly influences weather patterns. This jet stream forms at the boundary between cold polar air and warmer mid-latitude air, creating a strong temperature gradient that drives its flow. The polar jet stream plays a crucial role in steering weather systems and can impact conditions such as storms, temperature fluctuations, and precipitation across various regions.
Radiosondes: Radiosondes are lightweight, battery-powered instruments carried aloft by weather balloons that collect and transmit meteorological data from the atmosphere as they ascend. These devices measure temperature, humidity, pressure, and wind speed/direction, providing crucial information for understanding atmospheric conditions and forecasting weather events. The data obtained from radiosondes is vital for the analysis of phenomena such as jet streams, which significantly influence global weather patterns.
Rossby waves: Rossby waves are large-scale, meandering patterns in the jet stream that influence weather and climate systems across the globe. They are essential for understanding the dynamics of anticyclones and cyclones, playing a crucial role in the distribution of high and low-pressure systems in the atmosphere. These waves are formed due to the Earth's rotation and variations in temperature, resulting in the characteristic undulating motion that impacts weather patterns.
Seasonal shifts: Seasonal shifts refer to the changes in weather patterns and atmospheric conditions that occur as the seasons transition from one to another. These shifts are closely linked to variations in solar energy, leading to changes in temperature, precipitation, and atmospheric circulation, which play a crucial role in shaping regional climates and influencing weather events across different areas.
Storm track: A storm track refers to the path that a storm follows as it moves through the atmosphere, influenced by various atmospheric conditions. The storm track is critical in determining where storms will develop, their intensity, and how they will impact different regions. Jet streams, which are fast-flowing air currents in the upper atmosphere, play a significant role in guiding storm tracks and shaping weather patterns.
Subtropical jet stream: The subtropical jet stream is a fast-flowing air current located in the upper levels of the atmosphere, typically between 20 to 30 degrees latitude in both hemispheres. This jet stream plays a significant role in influencing weather patterns and climate by separating tropical air from polar air and affecting the formation and movement of storm systems.
Temperature gradients: Temperature gradients refer to the rate of temperature change in a specific direction, indicating how temperature varies over a given distance. These gradients play a crucial role in atmospheric processes, affecting wind patterns and the formation of weather systems, especially at the boundaries between different air masses.
Thermal wind: Thermal wind refers to the vertical change in wind speed and direction with altitude, primarily influenced by temperature gradients in the atmosphere. It is essential for understanding jet streams, as these winds develop due to differences in temperature between air masses, causing the air to flow from areas of high pressure to low pressure at different altitudes. This phenomenon plays a significant role in shaping weather patterns and influencing atmospheric circulation.
Weather balloons: Weather balloons are large, helium or hydrogen-filled balloons that carry instruments called radiosondes into the atmosphere to collect meteorological data. They ascend to high altitudes, often reaching up to 30 kilometers, where they measure temperature, humidity, pressure, and wind speed, providing crucial information for understanding atmospheric conditions and predicting weather patterns.
Wind shear: Wind shear is the variation in wind speed and direction over a short distance in the atmosphere. This phenomenon can greatly influence weather systems, especially during the development of severe storms and cyclones, as well as impacting aviation and energy generation.
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