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Jet stream

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Template:Otheruses2 [[Imageof the relation is such that temperatures decreasing polewards implies that winds develop a larger eastward component as one moves =jet-stream1 Jet Stream.] Retrieved on 2008-05-08.</ref>

===Subtropical 

Rozell. Amazing flying machines allow time travel. Retrieved on 2008-05-08.</ref>  Within North America, the time needed to fly east across the continent can be decreased by about 30 minutes if an airplane can fly with the jet stream, or increased by more than that amount if it must fly west against it.

Associated with jet streams is a phenomenon known as clear air turbulence (CAT), caused by vertical and horizontal windshear connected to the jet streams.[1] The CAT is strongest on the cold air side of the jet,[2] next to and just underneath the axis of the jet.[3] Clear air turbulence can be hazardous to aircraft, and has caused fatal accidents, such as United Airlines Flight 826 (1997).[4][5]

Future power generation

Scientists are investigating ways to harness the wind energy within the jet stream. According to one estimate, of the potential wind energy in the jet stream, only 1 percent would be needed to meet the world's current energy needs. The required technology would reportedly take 10–20 years to develop.[6]

Unpowered aerial attack

Towards the end of World War II the Japanese fire balloon was designed as a cheap weapon intended to make use of the jet stream over the Pacific Ocean to reach the west coast of Canada and the United States. They were relatively ineffective as weapons and were used in one of the few attacks on North America during World War II, causing six deaths and a small amount of damage.[7]

Changes due to climate cycles

Effects of ENSO

Impact of El Niño and La Niña on North America
Main article: Effects of the El Niño-Southern Oscillation in the United States

The changing of the normal location of upper-level jet streams can be anticipated during phases of the El Niño-Southern Oscillation (ENSO), which leads to consequences precipitation-wise and temperature-wise across North America, affects tropical cyclone development across the eastern Pacific and Atlantic basins. Combined with the Pacific Decadal Oscillation, ENSO can also impact cold season rainfall in Europe.[8] Changes in ENSO also change the location of the jet stream over South America, which partially effects precipitation distribution over the continent.[9]

El Niño

During El Niño events, increased precipitation is expected in California due to a more southerly, zonal, storm track.[10] During the El Niño portion of ENSO, increased precipitation falls along the Gulf coast and Southeast due to a stronger than normal, and more southerly, polar jet stream.[11] Snowfall is greater than average across the southern Rockies and Sierra Nevada mountain range, and is well-below normal across the Upper Midwest and Great Lakes states.[12] The northern tier of the lower 48 exhibits above normal temperatures during the fall and winter, while the Gulf coast experiences below normal temperatures during the winter season.[13][14] The subtropical jet stream across the deep tropics of the Northern Hemisphere is enhanced due to increased convection in the equatorial Pacific, which decreases tropical cyclogenesis within the Atlantic tropics below what is normal, and increases tropical cyclone activity across the eastern Pacific.[15] In the Southern Hemisphere, the subtropical jet stream is displaced equatorward, or north, of its normal position, which diverts frontal systems and thunderstorm complexes from reaching central portions of the continent.[9]

La Niña

Across North America during La Niña, increased precipitation is diverted into the Pacific Northwest due to a more northerly storm track and jet stream.[16] The storm track shifts far enough northward to bring wetter than normal conditions (in the form of increased snowfall) to the Midwestern states, as well as hot and dry summers.[17][18] Snowfall is above normal across the Pacific Northwest and western Great Lakes.[19] Across the North Atlantic, the jet stream is stronger than normal, which directs stronger systems with increased precipitation towards Europe.[20]

The Dust Bowl

Evidence suggests the jet stream was at least partially responsible for the widespread drought conditions during the 1930s Dust Bowl in the Midwest United States. Normally, the jet stream flows east over the Gulf of Mexico and turns northward pulling up moisture and dumping rain onto the Great Plains. During the Dust Bowl, the jet stream weakened and changed course traveling farther south than normal. This starved the Great Plains and other areas of the Midwest of precious rain creating dusty conditions.[21]

Longer-term climatic changes

During 2007, 2008, 2009 the Jet Stream has been at an abnormally low latitude across the UK, lying closer to the English Channel, around 50°N rather than its more usual north of Scotland latitude of around 60°N. However, between 1979 and 2001, it has been found that the position of the jet stream has been moving northward at a rate of 2.01 kilometres (1.25 mi) per year across the Northern Hemisphere. Across North America, this type of change could lead to drier conditions across the southern tier of the United States and more frequent and more intense tropical cyclones in the tropics. A similar slow poleward drift was found when studying the Southern Hemisphere jet stream over the same time frame.[22]

Other upper-level jets

Polar night jet

The polar-night jet stream forms only during the winter months (i.e. polar nights) of the year in their respective hemispheres at around 60° latitude, but at a greater height than the polar jet, of about 80,000 feet.[23] During these dark months the air high over the poles becomes much colder than the air over the Equator. This difference in temperature gives rise to extreme air-pressure differences in the stratosphere which, when combined with the Coriolis effect, create the polar night jets which race eastward at altitudes of about 30 miles.[24] Inside the polar night jet is the polar vortex. The warmer air can only move along the edge of the polar vortex, but not enter it. Within the vortex, the cold polar air becomes cooler and cooler with neither warmer air from lower latitudes nor energy from the sun during the polar night.[25]

Low level jets

There are wind maxima at lower levels of the atmosphere that are also referred to as jets.

Barrier jet

A barrier jet in the low levels forms just upstream of mountain chains, with the mountains forcing the jet to be oriented parallel to the mountains. The mountain barrier increases the strength of the low level wind by 45 percent.[26] A southerly low-level jet in the Great Plains helps fuel overnight thunderstorm activity during the warm season, normally in the form of mesoscale convective systems which form during the overnight hours.[27] A similar phenomenon develops across Australia, which pulls moisture poleward from the Coral Sea towards cut-off lows which form mainly across southwestern portions of the continent.[28]

Africa

The mid-level African easterly jet which occurs during the Northern Hemisphere summer between 10°N and 20°N above West Africa, and the nocturnal poleward low-level jet in the Great Plains.[29] The low-level easterly African jet stream is considered to play a crucial role in the southwest monsoon of Africa,[30] and helps form the tropical waves which march across the tropical Atlantic and eastern Pacific oceans during the warm season.[31] The formation of the thermal low over northern Africa leads to a low-level westerly jet stream from June into October.[32]

See also

References

  1. ^ BBC. Jet Streams in the UK. Retrieved on 2008-05-08.
  2. ^ M. P. de Villiers and J. van Heerden. Clear air turbulence over South Africa. Retrieved on 2008-05-08.
  3. ^ CLARK T. L., HALL W. D., KERR R. M., MIDDLETON D., RADKE L., RALPH F. M., NEIMAN P. J., LEVINSON D. Origins of aircraft-damaging clear-air turbulence during the December 9, 1992 Colorado downslope windstorm : Numerical simulations and comparison with observations. Retrieved on 2008-05-08.
  4. ^ National Transportation Safety Board. Aircraft Accident Investigation United Airlines flight 826, Pacific Ocean December 28, 1997. Retrieved on 2008-05-13.
  5. ^ Staff writer (December 29, 1997). "NTSB investigates United Airlines plunge". CNN. Retrieved 2008-05-13.
  6. ^ Keay Davidson. Scientists look high in the sky for power. Retrieved on 2008-05-08.
  7. ^ The Fire Balloons
  8. ^ Davide Zanchettin, Stewart W. Franks, Pietro Traverso, and Mario Tomasino. On ENSO impacts on European wintertime rainfalls and their modulation by the NAO and the Pacific multi-decadal variability described through the PDO index. Retrieved on 2008-05-13.
  9. ^ a b Caio Augusto dos Santos Coelho and Térico Ambrizzi. 5A.4. Climatological Studies of the Influences of El Niño Southern Oscillation Events in the Precipitation Pattern Over South America During Austral Summer. Retrieved on 2008-05-13.
  10. ^ John Monteverdi and Jan Null. WESTERN REGION TECHNICAL ATTACHMENT NO. 97-37 NOVEMBER 21, 1997: El Niño and California Precipitation. Retrieved on 2008-02-28.
  11. ^ Climate Prediction Center. El Niño (ENSO) Related Rainfall Patterns Over the Tropical Pacific. Retrieved on 2008-02-28.
  12. ^ Climate Prediction Center. ENSO Impacts on United States Winter Precipitation and Temperature. Retrieved on 2008-04-16.
  13. ^ Climate Prediction Center. Average October-December (3-month) Temperature Rankings During ENSO Events. Retrieved on 2008-04-16.
  14. ^ Climate Prediction Center. Average December-February (3-month) Temperature Rankings During ENSO Events. Retrieved on 2008-04-16.
  15. ^ "How do El Niño and La Nina influence the Atlantic and Pacific hurricane seasons?" (FAQ). Climate Prediction Center. Retrieved 2008-03-21.
  16. ^ Nathan Mantua. La Niña Impacts in the Pacific Northwest. Retrieved on 2008-02-29.
  17. ^ Southeast Climate Consortium. SECC Winter Climate Outlook. Retrieved on 2008-02-29.
  18. ^ Reuters. La Nina could mean dry summer in Midwest and Plains. Retrieved on 2008-02-29.
  19. ^ Climate Prediction Center. ENSO Impacts on United States Winter Precipitation and Temperature. Retrieved on 2008-04-16.
  20. ^ Paul Simons and Simon de Bruxelles. More rain and more floods as La Niña sweeps across the globe. Retrieved on 2008-05-13.
  21. ^ Weather at About.com. Causes of the Dust Bowl in the United States. Retrieved on 2008-06-10.
  22. ^ Associated Press. Jet stream found to be permanently drifting north. Retrieved on 2008-05-08.
  23. ^ "Jet Streams around the World". BBC.
  24. ^ Gedney, Larry (1983). "The Jet Stream". University of Alaska Fairbanks.
  25. ^ "2002 Ozone-Hole Splitting - Background". Ohio State University.
  26. ^ J. D. Doyle. The influence of mesoscale orography on a coastal jet and rainband. Retrieved on 2008-12-25.
  27. ^ Matt Kumijan, Jeffry Evans, and Jared Guyer. The Relationship of the Great Plains Low-Level Jet to Nocturnal MCS Development. Retrieved on 2008-05-08.
  28. ^ L. Qi, L.M. Leslie, and S.X. Zhao. Cut-off low pressure systems over southern Australia: climatology and case study. Retrieved on 2008-05-08.
  29. ^ Dr. Alex DeCaria. Lesson 4 – Seasonal-mean Wind Fields. Retrieved on 2008-05-03.
  30. ^ Kerry H. Cook. Generation of the African Easterly Jet and Its Role in Determining West African Precipitation. Retrieved on 2008-05-08.
  31. ^ Chris Landsea. AOML Frequently Asked Questions. Subject: A4) What is an easterly wave ? Retrieved on 2008-05-08.
  32. ^ B. Pu and K. H. Cook (2008). Dynamics of the Low-Level Westerly Jet Over West Africa. American Geophysical Union, Fall Meeting 2008, abstract #A13A-0229. Retrieved on 2009-03-08.
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