Jet Streams

Introduction

A jet stream is a current of wind flowing fast across the Earth’s atmosphere. It is often seen blowing through the troposphere in a horizontal direction. It flows from a westerly direction to the east, often reaching 20,000 to 50,000 feet altitude. The jet stream is created due to the difference in temperature at the junction of two different air masses. The velocity of wind within the jet stream increases proportionally to the difference in temperature. Jet streams have been identified at 20 degrees latitude along both hemispheres. A jet stream extends to the poles.

Discovery of the Jet Stream

The jet stream was first observed in 1883 with the eruption of the Krakatoa volcano. Weather conditions were studied carefully after the volcano erupted, and the effects on the atmosphere and sky were tracked for multiple years afterwards. This strange phenomenon was termed the “equatorial smoke stream”. Wasaburo Oishi noticed a similar occurrence near Mount Fuji, Japan, during the 1920s. However, Wiley Post, an American pilot, is credited for discovering the jet stream in 1933. He noticed the phenomenon as he flew around the world. He observed it by flying above 6200 metres, donning a pressurised suit. The existence of the jet stream was noted and commented upon by fighter pilots who traversed through the world during World War II.

Characteristics of the Jet Stream

• There is a thermal gradient formed between the pole and equator

• A pressure gradient was observed in the same area too

• There is another pressure gradient observed between the surface and subsurface air, notably over both the poles

• The jet stream remains the strongest at 9 to 12 kilometres above sea level

• The subtropical jet stream is much weaker at 10 to 16 kilometres

• Both the Northern and the Southern Hemisphere experience jet streams at polar & subtropical levels

• The thermal contrast between the Hadley and Ferrel cells results in the formation of a jet stream

• The whirlwind-like wave of the stream is known as the Rossby Wave

• The Southward shift in pressure belts is observed in winters with the Equatorial expansion of the jet streams

• An increase in thermal intensity and extended pressure area at the poles increases the intensity of the speed of jet streams in winter

Causes of the jet stream

The jet stream is caused due to differences in temperature in air masses. With sunlight failing to reach every part of the globe equally, portions of the Earth remain cooler than the others. This results in more hot air near the equator and cool air at the poles. The warm air rises rapidly as it expands and creates an air current. The vacant spot is filled with cool air that creates a cooler air current simultaneously. Jet streams are formed when air masses of varying temperatures come together at a higher altitude, namely the troposphere.

Types of jet streams

According to their location and directional aspects, five different types of jet streams are termed according to their location and directional aspects. They include the following:-

1. Polar Front Jet Stream: These streams are formed above the converging point of 40 degrees to 60 degrees latitude as the cold polar air meets the warm air mass from the tropics. The thermal gradient is thus increased, and the stream moves in an easterly direction. However, the formation of such streams is not regular.

2. Subtropical Westerly Jet Streams: This stream moves in the upper troposphere in the northern direction to the high-pressure belt of the subtropical surface. It is formed above 30° to 35° latitudes. This is a fairly regular phenomenon, with the air circulating west to east.

3. Tropical Easterly Jet Stream: The jet streams that develop in the tropics in the upper troposphere and above the surface eastern winds are observed above India and Africa predominantly. It occurs due to the heating up of the Tibetan Plateau. These jet streams are responsible for Indian monsoons as well.

4.  Polar Night Jet Streams: These streams develop under the stratospheric layer during the winter. The steep thermal gradient enhances the velocity of winds that follows a westerly circulation. The velocity tends to decrease during summers as the direction is reversed.

5. Local Jet Streams– The locally formed jet streams are not a universal phenomenon. They are limited by the local conditions, with their importance being less significant.

Uses of Jet streams

• Aviation– Jet stream was first used to cut the time of flying. A commercial flight from Honolulu to Tokyo was reduced by 6.5 hours, courtesy of the jet stream. This was first observed in 1952, and a trend of using jet streams effectively to reduce time and fuel usage became popular thereafter

• Weather– Meteorological Offices across the world can now predict weather conditions by studying the jet streams

• Power Generation– Scientists studying weather patterns are trying to harness the power of wind trapped within the jet streams. Being able to use only 1% of the energy can help to solve the energy crisis

Conclusion

Jet streams are fast-flowing currents of air observed in both hemispheres. The difference in temperature between two separate air masses triggers the phenomenon. Discovered in the 19th century, jet streams help us accurately o predict weather patterns. It is also responsible for Indian monsoons. The usage of jet streams has succeeded in decreasing flight times significantly, while a way to harness its wind power can solve the energy crisis in the future.