Notes on Jet streams

Jet streams are intense air currents that circumnavigate the globe in an eastward direction at a height of 10–15 km in both the Northern and Southern Hemispheres. Jet streams are essential because they form weather systems—both low and high pressure areas—and guide them across the midlatitudes. They exist because of temperature disparities between low and high latitudes, as well as the Earth’s rotation. Jet streams do not generally run in a straight line from west to east, but instead meander in alternating troughs and ridges. Rossby waves are the name for these waves. The conservation of vorticity is directly responsible for their existence.

Types of Jet Streams

The Jets’ origin is supported by three types of gradients

• Temperature difference between the poles and the equator
• Difference of pressure between the poles and the equator
• Over the poles, the pressure gradient between surface and subsurface air.

There are two major types:

• The subtropical jet stream
• The mid-latitude or polar front jet stream

Subtropical Westerly Jet Stream

They travel north of the subtropical high-pressure belt in the upper troposphere in both hemispheres above 30 degrees to 35 degrees latitude.

Their movement from west to east is more regular than that of the polar front jet stream.

It is produced by the earth’s rotation and flows for the majority of the year.

Polar Front Jet Stream

They form above the convergence zone of the polar cold and tropical warm air masses above the surface (40 degrees and 60 degrees latitude).

Because two contrasting air masses have collided, the thermal gradient is considerable.

These jets travel eastward and have a more changeable position than the subtropical jet.

Characteristics of Jet streams

• Jet streams flow from west to east due to the Earth’s rotation. The circulation is commonly detected between the poles and 20 degrees latitude in both hemispheres
• Because they migrate about the poles in both hemispheres, they are also known as circumpolar
• On the trajectory , their circulation pattern is wavy and meandering
• During the summer , the spread narrows due to the northward shift, but during the winter , it can reach up to 20 degrees latitude
• These can span up to 40 kilometres in width and 2-3 kilometres in depth.
• With a winter low of roughly 120 km /h and a summer high of 50 km /h , the average wind speed is exceptionally high
• The highest wind velocity is measured at the crest and trough of the jet stream
• It runs along the southern slopes of the Himalayas in the winter and swings northwards in the summer, flowing along the Himalayan edge (early June) . Also in late summer, between July and August, along the Tibetan Plateau’s northern edge.

Climatic Significance

• They have a big influence on regional and local weather patterns
• The intensity of temperate cyclones and jet streams have a tight link. When jet streams intersect with surface wind systems , catastrophic storms develop
• They also assist in providing a relatively clear picture of the incidence of El Nino and La Nina episodes
• Aviators also employ them when flying in the direction of the jet streams When flying in the opposite direction of the jet streams, however, aviators avoid them since jet streams are unpredictable and can cause unexpected movement even when the weather appears calm and clear
• South Asia’s monsoon is heavily influenced and controlled by jet streams
• Monsoons are also reliant on upper air circulation, which is governed by Subtropical Jet Streams. The tropical easterly stream, which is found between 8 and 35 degrees north latitude, is linked to the southwest monsoon in India. The northeast monsoon is associated with the subtropical westerly Jet Stream, which blows between 20 and 35 degrees latitude in both hemispheres during the winter
• They’re also recognised for transporting ozone-depleting compounds into the stratosphere, assisting in ozone layer depletion by functioning as a vehicle.

Conclusion

Jet streams play an important part in weather forecasting because they split colder and warmer air. Jet streams shift air masses around, causing weather systems to move to new places or even stall if they have moved too far away.