Jet Streams: Definition, Speed and Causes

• Jet streams are fast-moving air currents high in Earth's atmosphere, typically 5 to 9 miles (8 to 15 kilometers) high.
• They are located in the tropopause, the boundary between the troposphere and stratosphere.
• Jet streams are important for weather prediction, moving cool and warm air to different parts of the Earth.
• These winds blow eastward, shifting north and south based on temperature differences.

Speed

• Jet streams contain some of the fastest winds in the atmosphere.
• They can reach speeds of 80 to 140 mph (129 to 225 kph).
• The fastest jet stream winds have been reported at 275 mph.
• Winds are faster in winter when temperature differences between air currents are greatest.

Causes

• Uneven heating from the sun causes temperature differences on Earth, with warmer air near the equator and colder air near the poles.
• Air moves between these regions, creating differences in air pressure.
• Warm air expands and becomes lighter, creating a warm air current.
• Cooler, denser air pushes to replace the warm air, creating a cool air current.
• Cool air has molecules closer together, creating more pressure than warm air.

Pressure Gradient

• Differences in temperature and pressure create a gradient.
• Air flows down this gradient from high to low pressure areas.
• The Earth's rotation causes the Coriolis force, deflecting air in each hemisphere.
• Air deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Types

• There are typically two main jet streams: subtropical and polar-front.
• The subtropical jet stream is located at approximately 30 degrees latitude.
• The polar front jet stream's position varies between the polar and temperate air boundary.
• A reverse jet stream blows west in tropical altitudes during the Northern Hemisphere's summer.
• This reverse jet stream often causes summer monsoons in the Indian Ocean.

Coriolis Force

• The Coriolis force affects the direction of unsecured objects traveling long distances around Earth.
• It determines the direction of deflection of air currents based on the hemisphere.
• Earth's rotation causes this effect; it spins faster near the Equator and slower at the poles.
• The impact of the Coriolis effect depends on the velocity of Earth or the velocity of the object being deflected.
• High speeds or long distances experience more significant effects.

Polar Front

• Polar fronts occur when cold air from polar regions meets warmer air from tropical regions.
• This boundary between cold and warm air masses is typically thousands of miles long.
• It usually falls mid-latitude on Earth.
• Arctic air is much colder than air from tropical regions.

Polar Jet Stream

• The polar jet stream exists high in the atmosphere between warm air from the equator and cool air from the poles.
• It is also known as the mid-latitude jet stream.
• It is the most powerful jet stream due to its ability to move south in winter and north in summer.
• It dips very far south in winter, bringing cold temperatures.
• The wind in this jet stream travels faster closer to the equator and slower closer to the poles.
• Both the Northern and Southern Hemispheres have polar jet streams.
• Air moves faster in the Northern Hemisphere.
• Polar jet streams are typically located around 50 to 60 degrees latitude.

Jet streams are fast-moving air currents in Earth's atmosphere, located in the tropopause. They move cool and warm air, blowing eastward and shifting with temperature differences. The streams contain winds between 80 to 140 mph, and are faster in the winter.