3.3 Jet streams and Rossby waves
5 min read•august 16, 2024
Jet streams and are key players in atmospheric circulation. These high-altitude wind patterns and large-scale atmospheric waves shape global weather and climate. They're like the conductors of Earth's atmospheric orchestra, directing the flow of air masses and weather systems.
Understanding these phenomena is crucial for grasping how our atmosphere works. Jet streams steer storms and influence temperature patterns, while Rossby waves create persistent weather conditions. Together, they're the backbone of mid-latitude weather systems and play a big role in extreme events.
Jet streams and their formation
Characteristics and structure of jet streams
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- Narrow bands of strong winds in upper troposphere and lower stratosphere
- Occur at altitudes of 9-16 km
- Core wind speeds reach 120-250 km/h
- Two main jet streams in each hemisphere (polar and subtropical)
- located between 50° and 60° latitude
- found around 30° latitude
- Exhibit seasonal variations with stronger winds in winter months
Formation and driving factors
- Temperature gradient between equatorial and polar regions drives jet stream formation
- Earth's rotation () contributes to jet stream development
- Thermal wind balance maintains jet stream structure
- Enhanced by upper-level convergence and divergence patterns
- Influenced by topography and land-sea temperature contrasts
- Strengthened by latitudinal temperature gradients in the stratosphere
- Affected by tropical convection and teleconnection patterns (, )
Role in atmospheric circulation
- Significantly influence global atmospheric circulation patterns
- Act as boundaries between cold polar air and warm tropical air masses
- Guide the movement of weather systems across continents
- Play crucial role in formation and movement of mid-latitude cyclones and anticyclones
- Influence the distribution of precipitation and temperature anomalies
- Affect the transport of heat, moisture, and momentum in the atmosphere
- Contribute to the development of planetary wave patterns (Rossby waves)
Rossby waves: Characteristics and types
Fundamental properties of Rossby waves
- Large-scale meanders in high-altitude winds
- Result from Earth's rotation and spherical shape
- Long wavelengths spanning thousands of kilometers
- Slow westward propagation relative to main flow
- Governed by conservation of absolute vorticity
- Exhibit unique dispersion relationship
- Longer waves move westward relative to mean flow
- Shorter waves move eastward relative to mean flow
Types and generation mechanisms
- Two main types (free Rossby waves and forced Rossby waves)
- Free Rossby waves arise naturally from conservation of potential vorticity
- Forced Rossby waves generated by external factors
- External factors include topography (Rocky Mountains, Himalayas)
- Land-sea temperature contrasts contribute to forced wave generation
- Tropical convection patterns (Madden-Julian Oscillation) influence wave formation
- Baroclinic instability in mid-latitudes can trigger Rossby wave development
Factors influencing wave characteristics
- Amplitude affected by latitudinal gradient of potential vorticity
- Phase speed influenced by strength of background zonal flow
- Wavelength determined by atmospheric stability and vertical wind shear
- Beta effect (variation of Coriolis parameter with latitude) crucial for wave propagation
- Stratospheric conditions impact downward propagation of waves
- Seasonal changes in temperature gradients affect wave intensity
- Interaction with jet streams modulates wave growth and decay
Rossby waves and jet stream meandering
Interaction between Rossby waves and jet streams
- Rossby waves intimately connected to meandering patterns in jet streams
- Particularly evident in polar jet stream behavior
- Lead to development of troughs (southward dips) and ridges (northward bulges)
- Wavelength of Rossby waves determines scale of jet stream meandering
- Longer waves produce larger amplitude meanders
- Wave amplification causes jet stream to develop steep troughs and ridges
- Phase speed of waves relative to jet stream influences persistence of weather patterns
Mechanisms of wave-jet stream coupling
- Potential vorticity conservation drives mutual interaction
- Baroclinic instability enhances wave growth and jet stream deformation
- Wave breaking occurs when amplitudes become too large
- Breaking results in irreversible mixing of air masses
- Significant alterations to jet stream structure follow wave breaking events
- Momentum fluxes associated with waves affect jet stream intensity
- Thermal advection by waves modifies temperature gradients supporting jet
Atmospheric blocking and extreme events
- Rossby wave amplification can lead to
- Blocks cause persistent high and low pressure systems
- Result in prolonged periods of specific weather conditions (heatwaves, cold spells)
- Omega blocks characterized by high pressure flanked by two lows
- Rex blocks feature high-latitude high pressure adjacent to low-latitude low
- Blocks can persist for days to weeks, significantly impacting regional weather
- Associated with extreme events like droughts, floods, and temperature anomalies
Jet streams and Rossby waves: Impact on weather
Influence on mid-latitude weather systems
- Jet streams act as steering currents for cyclones and anticyclones
- Position relative to developing storm systems enhances or inhibits growth
- Upper-level divergence and convergence associated with affect storm intensity
- Rossby wave patterns create regions of persistent high and low pressure
- Amplified waves can result in atmospheric blocking, causing stationary weather patterns
- Jet stream configurations create favorable conditions for severe weather outbreaks
- Strong wind shear associated with jet streams supports supercell thunderstorm development
Regional climate and extreme events
- Interaction influences distribution of temperature and precipitation anomalies
- Persistent wave patterns lead to prolonged heat waves or cold spells
- Jet stream position affects storm tracks and frequency of precipitation
- Amplified waves can cause extreme events like floods or droughts
- Changes in patterns due to climate change shift regional weather patterns
- Altered jet stream behavior impacts frequency and intensity of extreme events
- Weakening of polar jet stream associated with increased Arctic warming (Arctic amplification)
Global teleconnections and long-term variability
- Rossby waves facilitate atmospheric teleconnections between distant regions
- Pacific North American (PNA) pattern influenced by Rossby wave trains
- North Atlantic Oscillation (NAO) linked to jet stream and wave configurations
- El Niño-Southern Oscillation (ENSO) modulates global Rossby wave patterns
- Long-term changes in wave characteristics affect monsoon systems (Indian, African)
- Stratospheric sudden warmings propagate downward through Rossby wave breaking
- Quasi-Biennial Oscillation (QBO) in stratosphere impacts tropospheric wave patterns
Key Terms to Review (18)
Arctic Oscillation: The Arctic Oscillation (AO) is a climate pattern characterized by fluctuating pressure systems over the Arctic and mid-latitudes, influencing weather patterns in the Northern Hemisphere. It describes the variability in atmospheric pressure between the Arctic region and the lower latitudes, affecting the strength and position of the polar jet stream, which plays a critical role in shaping weather systems and temperature distributions.
Barotropic instability: Barotropic instability refers to a type of atmospheric instability that occurs when the horizontal temperature gradient is present in a barotropic atmosphere, where density is constant throughout. This instability typically arises in large-scale weather patterns and is closely related to the dynamics of jet streams and Rossby waves, as it can lead to the development of cyclones and other weather systems. Understanding barotropic instability helps explain how these atmospheric features evolve and interact with each other.
Blocking patterns: Blocking patterns are large-scale atmospheric circulation systems that impede the normal flow of air masses, often causing persistent weather conditions. These patterns can lead to extended periods of dry or wet weather and are closely linked to the behavior of jet streams and Rossby waves, which play a crucial role in shaping global weather patterns and influencing local climates.
Carl-Gustaf Rossby: Carl-Gustaf Rossby was a Swedish meteorologist renowned for his groundbreaking work in atmospheric dynamics, particularly regarding the study of jet streams and Rossby waves. His research contributed significantly to our understanding of how these large-scale patterns in the atmosphere influence weather and climate, highlighting the role of the Earth's rotation on fluid motion in the atmosphere.
Clear air turbulence: Clear air turbulence (CAT) refers to unpredictable and sudden changes in airflow that occur at high altitudes, typically above 15,000 feet, away from thunderstorms and other visible weather phenomena. This type of turbulence is primarily associated with the presence of jet streams and can significantly affect aircraft during flight, causing unexpected jolts that can be dangerous to passengers and crew.
Cold fronts: Cold fronts are boundaries that separate a mass of cold air from a mass of warm air, typically moving into the area with colder temperatures. As the cold air advances, it lifts the warm air upwards, leading to various weather changes, including precipitation and shifts in wind direction. This process is closely related to atmospheric dynamics, particularly involving jet streams and Rossby waves, which influence the movement and behavior of these fronts.
Coriolis Effect: The Coriolis Effect is the apparent deflection of moving objects, such as air and water, due to the rotation of the Earth. This phenomenon significantly influences weather patterns, ocean currents, and atmospheric circulation by causing moving air and water to turn and twist rather than move in a straight line, which is crucial for understanding global climate dynamics.
Edward Norton Lorenz: Edward Norton Lorenz was an American mathematician and meteorologist, best known for his pioneering work in chaos theory and its applications to weather forecasting. His research highlighted the sensitivity of complex systems to initial conditions, famously illustrated by the 'butterfly effect,' which describes how small changes can lead to vastly different outcomes in weather patterns and climate systems.
El Niño: El Niño is a climate pattern characterized by the periodic warming of sea surface temperatures in the central and eastern Pacific Ocean, significantly impacting global weather patterns. This phenomenon can disrupt normal weather conditions, leading to alterations in precipitation, temperature, and storm activity around the world, affecting various climate zones.
Extratropical cyclones: Extratropical cyclones are large-scale weather systems that form outside of the tropics, characterized by low-pressure centers and typically associated with fronts. These cyclones play a significant role in the weather patterns of mid-latitude regions, bringing changes in temperature, precipitation, and wind as they move through the atmosphere. They are closely linked to the dynamics of jet streams and Rossby waves, which influence their formation and path.
Geostrophic balance: Geostrophic balance refers to the equilibrium between the Coriolis force and the pressure gradient force, which is crucial for understanding large-scale atmospheric motions. This balance allows for the formation of geostrophic winds that flow parallel to isobars, providing insight into the behavior of jet streams and Rossby waves. The concept is essential in explaining how wind patterns develop in the upper levels of the atmosphere, where friction is minimal.
Jet streaks: Jet streaks are fast-moving segments within a jet stream that can significantly influence weather patterns by enhancing or diminishing the development of storms. These localized areas of strong winds typically exist on the poleward side of the jet stream, creating variations in pressure and impacting the vertical motion of air, which plays a crucial role in cloud formation and precipitation.
Jet stream index: The jet stream index is a numerical representation used to quantify the position and strength of jet streams in the atmosphere, particularly focusing on their effects on weather patterns. This index helps in understanding how the jet streams influence temperature, precipitation, and storm tracks by indicating their location and intensity. By analyzing the jet stream index, meteorologists can better predict significant weather events that are tied to the behavior of these high-altitude winds.
La Niña: La Niña is a climate pattern characterized by cooler-than-average sea surface temperatures in the central and eastern Pacific Ocean, which can influence weather patterns globally. It is often seen as the opposite phase of El Niño and plays a crucial role in the climate variability that affects tropical, temperate, and polar regions.
Polar jet stream: The polar jet stream is a fast-flowing ribbon of air located high in the atmosphere, typically around 30,000 feet, that separates cold polar air from warmer air to the south. This powerful wind current plays a crucial role in influencing weather patterns and systems, particularly in mid-latitude regions, by guiding storms and affecting temperature distributions.
Quasi-stationary waves: Quasi-stationary waves are atmospheric waves that maintain a relatively constant position and amplitude over time, often observed in the mid-latitudes. These waves play a significant role in the distribution of weather patterns and are closely linked to jet streams and Rossby waves, which shape the movement of air masses and influence the development of cyclones and anticyclones in the atmosphere.
Rossby waves: Rossby waves are large-scale atmospheric waves that occur in the mid-latitudes due to the rotation of the Earth and the presence of the jet streams. These waves play a crucial role in shaping weather patterns, influencing the movement of high and low-pressure systems, and affecting temperature distributions across the globe. They are essential for understanding how weather systems interact and evolve over time.
Subtropical jet stream: The subtropical jet stream is a fast-flowing ribbon of air located at approximately 30 degrees latitude in both hemispheres, characterized by westerly winds that can reach speeds of up to 200 mph. This jet stream plays a vital role in the global atmospheric circulation and influences weather patterns, including the development of storms and precipitation in various regions.