Atmospheric jet streams were discovered towards the end of World War II by U.S. bomber pilots over Japan and by German reconnaissance aircraft over the Mediterranean. The World Meteorological Organization defines a jet stream as a strong, narrow air current that is concentrated along nearly horizontal axis in the upper troposphere or stratosphere (10 to 50 kmaltitude), characterized by wind motions that produce strong vertical lateral shearing action and featuring one or more velocity maximum. Normally a jet stream is thousands of kilometers long, hundreds of kilometers wide and several kilometers deep. The vertical wind shear is of the order of 5 to 10 m/sec per kilometer, and the lateral shear is of the order of 5 m/sec per 100 km. An arbitrary lower limit of 30m/sec is assigned to the speed of the wind along the axis of a jet stream.
With abundant radio-sonic data now available over the Northern Hemisphere it is possible to map the jet streams in the upper troposphere (near 10 to 12 km) in their daily occurrence and variation and to forecast them reasonably well with numerical prediction techniques.
Upper-air information from the Southern Hemisphere is still sparse. Constant-level balloons (the so-called GHOST balloons) and satellite information on temperature structure and characteristic cloud formations in the atmosphere are serving to close the data on the global jet stream distribution.
The strongest winds known in jet streams have been encountered over Japan, where speeds up to 500 km/hr (close to 300 knots) occur. A persistent band of strong winds occurs during the winter season over this region, flowing from the southwest and leading tropical air northern India into juxtaposition with polar and arctic air from Siberia. A similar region of confluence of air masses with vastly different temperatures exists over the central and eastern United States, leading to a maximum frequency of occurrence of jet streams during winter and spring.
The main impact on weather and climate comes from two distinct jet stream systems: the Polar- Front Jet Stream, which is associated with the air mass contracts (the fronts) of middle latitudes and which gives rise to the formation of squalls, storms, and cyclones in this latitude belt; and the Subtropical Jet Stream, which lies over the subtropical high-pressure belt, and which is characterized by predominant subsidence motions and, hence, with fair weather. During summer, a belt of strong easterly winds is found over Southeast Asia, India, the Arabian Sea, and tropical Africa, this tropical, easterly jet stream is linked with the weather disturbances of the Indian and African summer monsoons and their heavy rainfalls. Because jet streams have a great effect on aircraft flights, they are of considerable importance to aviation. On eastbound transoceanic flights, extra fuel, which takes up useful cargo space. Clear air turbulence (CAT) is often found in jet streams, and this turbulence, which leads to irregular aircraft motion, can be a hazard to passengers
An atmospheric jet stream is
Show Hint
- a rare phenomenon.
- three dimensional.
- concentrated in the northern hemisphere.
- more common in summer.
The Correct Option is B
Solution and Explanation
- Option (a) is incorrect because jet streams are not rare; they are mapped and forecast regularly, especially in the Northern Hemisphere.
- Option (c) is incorrect because while most studies are in the Northern Hemisphere, jet streams occur globally.
- Option (d) is incorrect because they are more common in winter, not summer.
Detailed studies of atmospheric streams have been made over
Show Hint
- South Africa
- Europe
- Australia
- Antarctica
The Correct Option is B
Solution and Explanation
- Options (a), (c), and (d) are incorrect as the passage does not mention detailed studies in those regions.
The atmospheric jet stream consists of
Show Hint
- cumulous clouds bearing saturated moisture.
- debris caused by meteorites.
- air currents.
- effluents from speeding aircraft.
The Correct Option is C
Solution and Explanation
- Option (a) is incorrect because clouds are not the defining component of jet streams.
- Option (b) is unrelated to jet streams.
- Option (d) confuses aircraft effects with natural atmospheric currents.
According to present knowledge, jet streams are caused when
Show Hint
- polar and Arctic air meet.
- air masses with considerably different temperatures meet.
- winds with different speeds meet.
- squalls, storms and cyclones get dispersed.
The Correct Option is B
Solution and Explanation
- Option (a) is incomplete because it omits the tropical air component.
- Option (c) is misleading — speed difference is a result, not the primary cause.
- Option (d) refers to weather effects, not the cause of jet streams.
Jet streams affect air-traffic by
I. delaying flights.
II. Increased fuel consumption.
III. Their propensity to cause accidents.
IV. Damaging the air frame.
Show Hint
- I, II, III & IV
- II & IV only
- II, III & IV only
- II & III only
The Correct Option is D
Solution and Explanation
- It does not say they delay flights (I) — eastbound flights can even be faster due to tailwinds.
- There is no mention of damaging the airframe (IV).
Thus, only II and III are correct.
The summer monsoon over India is caused by
Show Hint
- the rotation of the earth.
- jet streams from the subtropical regions.
- juxtaposition of tropical air with Arctic air in the upper atmosphere.
- a tropical and easterly jet stream.
The Correct Option is D
Solution and Explanation
- Options (a) and (c) are not directly relevant.
- Option (b) refers to subtropical jet streams, which are linked to fair weather, not monsoons.
The result of the Subtropical Jet Stream is
Show Hint
- the occurrence of cyclones.
- the prevalence of fair weather.
- head winds which affect air traffic.
- high wind speed over Japan.
The Correct Option is B
Solution and Explanation
- Option (a) refers to cyclones, which are associated with the Polar-Front Jet Stream.
- Option (c) is not specific to the subtropical stream.
- Option (d) refers to the strongest winds near Japan, which are in the polar front region.
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