A short note on Jet Stream

 A non-stop, spiral, rapid geostrophic wind that flows round the earth in the upper boundary of troposphere is called a JET STREAM. It is few thousand kilometers in length and some hundred kilometers in width. It flows in a narrow path and for this reason sometimes its speed becomes very high, about 320 km/h to 480 km/h (approx).

Jet streams were first discovered in the 1920s by a Japanese meteorologist named Wasaburo Ooishi. He used weather balloons to track upper level winds high above Mount Fuji. The term “jet stream” wasn't used until 1939, though; when German meteorologist first used the term in a research paper. Research and knowledge about jet streams increased during World War II, as pilots noticed variations in winds as they flew between North America and Europe. 

Origin

The temperature gradient derives from the differential solar heating of the spherical surface of the earth: the surface is generally warmest at the equator and grows progressively cooler as one moves pole ward. The centrifugal effects of the earth's rotation, often called the Coriolis force, deflect the north-south transport of heat from the equator to the poles into the predominantly east-west motion of the jet stream. The relative strength, or velocity, of the jet stream is proportional to the intensity of this thermal gradient. During the winter months, when the equator-to-pole temperature disparity is at its greatest, the jet stream reaches its maximum velocity. During the summer months, when the temperature gradient between the equator and the pole is considerably less (only about half the winter value), the jet stream reaches its minimum velocity.

Life Cycle

Source: www.theupsconline.com

      Jet Stream has a lifecycle or index cycle. Meteorologists explain 4 stages of this lifecycle. Those stages are:

•      i.              FIRST STAGE: In this stage, the jet stream locates in the polar region. The wind flows west to east ward. The pressure gradient becomes very high. It called HIGH ZONAL INDEX.

•                  SECOND STAGE: In this stage the jet stream moves from pole to equator ward. The amplitude of waves becomes bigger.

•     iii.       THIRD STAGE: In this stage, the curves of wind flow get much bigger, wave lengths get smaller but amplitude of wave length increases. In this stage, the velocity of wind speed can reach up to 320 km/h.

•     iv.        FOURTH STAGE: In the last stage, the jet stream reaches near the equator and makes a cold & heavier wind cell, surrounded by warm and lighter wind. This stage is called LOW ZONAL INDEX. It is a transition stage between a old jet stream & a new jet stream. 

Source: www.skepticalscience.com

Classifications

Meteorologists classify the jet stream in 7 different types in terms of direction of wind flow, velocity of wind, location and magnitude etc. Those types are- a) Subtropical Jet Stream, b) Polar Front Jet Stream, c) Arctic Front Jet Stream, d)Tropical Jet Stream, e) Stratospheric Jet Stream, f) Electro Jet Stream & g) Local Jet Stream.

Influence

Jets streams play a key role in determining the weather because they usually separate colder air and warmer air. Jet streams generally push air masses around, moving weather systems to new areas and even causing them to stall if they have moved too far away.

Climatologists say that changes in the jet streams are closely tied to global warming, especially the polar jet streams, because there is a great deal of evidence that the North and South poles are warming faster than the remainder of the planet. When the jets streams are warmer, their ups and downs become more extreme, bringing different types of weather to areas that are not accustomed to climate variations. If the jet stream dips south, for example, it takes the colder air masses with it.

Jet streams also have an impact on air travel and are used to determine flight patterns. An airplane can travel much faster, and save fuel, by getting “sucked up” in the jet stream.