Jet Streams | Geography for UPSC 2024 (Pre & Mains) PDF Download

 Page 1


 
JET STREAM  
 
 
 
 
 
? Jet streams are the strong air streams present in the upper 
troposphere. 
? Jet streams are winds that circle around the earth with poles as their 
centers. 
? The strong and rapidly moving circumpolar westerly air circulation in 
a narrow belt of few hundred kilometers width in the upper limit of 
troposphere is called jet stream.  
? The circulation of jet streams is from the west to east in a narrow belt 
of a few hundred kilometres width at the height of 7.5 -14 km in the 
upper troposphere.  
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JET STREAM  
 
 
 
 
 
? Jet streams are the strong air streams present in the upper 
troposphere. 
? Jet streams are winds that circle around the earth with poles as their 
centers. 
? The strong and rapidly moving circumpolar westerly air circulation in 
a narrow belt of few hundred kilometers width in the upper limit of 
troposphere is called jet stream.  
? The circulation of jet streams is from the west to east in a narrow belt 
of a few hundred kilometres width at the height of 7.5 -14 km in the 
upper troposphere.  
 
? Meteorologists came to know about the existence of jet stream during the 
second world war when American Fighter jets were obstructed by the 
flow of the Jetstream during their Bombing mission over Japan.  
? When the temperature contrast is maximum, jet stream flows in near 
straight path. But when temperature contrast reduces, the jet stream 
starts to follow a meandering path. 
? So meandering depends on temperature contrast (temperature 
gradient).A meander is called peak or ridge if it is towards poles and 
trough if it is towards equator. 
? The meandering jet streams are called Rossby Waves. The existence 
of these waves explains the low-pressure cells (cyclones) and high-
pressure cells (anticyclones). 
? Jet streams flow just below the Tropopause. 
? Polar jet streams flow 6 – 9 km above the ground and Sub-tropical jet 
streams flows 10 – 16 km above the grounds. 
 
PERMANENT  JET STREAMS  
1. POLAR FRONT JET STREAMS  
? Polar front jet streams are formed above the convergence zone 
(40-60° latitude) of the surface polar cold air mass and sub-
tropical warm air mass.  The thermal gradient is steepened 
because of convergence of two contrasting air masses.  
? This jet stream was discovered by Rossby and also known as the 
primary jet stream. 
? It has an average speed of 215km/hour and in some cases, the 
speed may become double of the average speed. 
? They have an important role in the management of latitudinal 
heat budget of the earth and it accomplishes it through the 
creation of various cyclones and anticyclones in the Middle-
Latitude. 
Page 3


 
JET STREAM  
 
 
 
 
 
? Jet streams are the strong air streams present in the upper 
troposphere. 
? Jet streams are winds that circle around the earth with poles as their 
centers. 
? The strong and rapidly moving circumpolar westerly air circulation in 
a narrow belt of few hundred kilometers width in the upper limit of 
troposphere is called jet stream.  
? The circulation of jet streams is from the west to east in a narrow belt 
of a few hundred kilometres width at the height of 7.5 -14 km in the 
upper troposphere.  
 
? Meteorologists came to know about the existence of jet stream during the 
second world war when American Fighter jets were obstructed by the 
flow of the Jetstream during their Bombing mission over Japan.  
? When the temperature contrast is maximum, jet stream flows in near 
straight path. But when temperature contrast reduces, the jet stream 
starts to follow a meandering path. 
? So meandering depends on temperature contrast (temperature 
gradient).A meander is called peak or ridge if it is towards poles and 
trough if it is towards equator. 
? The meandering jet streams are called Rossby Waves. The existence 
of these waves explains the low-pressure cells (cyclones) and high-
pressure cells (anticyclones). 
? Jet streams flow just below the Tropopause. 
? Polar jet streams flow 6 – 9 km above the ground and Sub-tropical jet 
streams flows 10 – 16 km above the grounds. 
 
PERMANENT  JET STREAMS  
1. POLAR FRONT JET STREAMS  
? Polar front jet streams are formed above the convergence zone 
(40-60° latitude) of the surface polar cold air mass and sub-
tropical warm air mass.  The thermal gradient is steepened 
because of convergence of two contrasting air masses.  
? This jet stream was discovered by Rossby and also known as the 
primary jet stream. 
? It has an average speed of 215km/hour and in some cases, the 
speed may become double of the average speed. 
? They have an important role in the management of latitudinal 
heat budget of the earth and it accomplishes it through the 
creation of various cyclones and anticyclones in the Middle-
Latitude. 
 
? It plays a very important role in the distribution of precipitation 
in the middle latitude. 
? Cyclogenesis in the Temperate region is associated with the crest 
of Polar Front jet and maximum cyclonic rainfall occurs ahead 
of the trough. 
? At the same time, these jets also determine the path and 
movement of Temperate Cyclone. 
2.  SUBTROPICAL WESTERLY JET STREAMS  
? Subtropical westerly jet streams move in polar the upper 
troposphere to the north of subtropical surface high pressure 
belt (at jet stream the poleward limit of the Hadley cell in both 
the hemispheres) i.e above 30Q-35() latitudes.  
? It plays an important role in the distribution of precipitation over the 
subtropical latitude. 
? It has a major role in bringing western disturbances to India during 
the winter season and thus provides crucial rainfall which is vital for 
Rabi Crop. 
? The trough of the subtropical jet stream experiences high pressure 
and thus associated with the Tropical Deserts; and below the crest, 
the low-pressure system (cyclogenesis) may develop. 
 
LOCAL JET STREAMS: 
1. TROPICAL EASTERLY JET STREAMS  
o Tropical easterly jet streams develop in the upper troposphere 
above surface easterly trade winds over India and Africa during 
summer season due to intense heating of Tibetan plateau and 
play important role in the mechanism of Indian monsoon. 
o It originates due to excessive heating of Tibetan Plateau during 
the summer season due to which low pressure(converging) sets 
Page 4


 
JET STREAM  
 
 
 
 
 
? Jet streams are the strong air streams present in the upper 
troposphere. 
? Jet streams are winds that circle around the earth with poles as their 
centers. 
? The strong and rapidly moving circumpolar westerly air circulation in 
a narrow belt of few hundred kilometers width in the upper limit of 
troposphere is called jet stream.  
? The circulation of jet streams is from the west to east in a narrow belt 
of a few hundred kilometres width at the height of 7.5 -14 km in the 
upper troposphere.  
 
? Meteorologists came to know about the existence of jet stream during the 
second world war when American Fighter jets were obstructed by the 
flow of the Jetstream during their Bombing mission over Japan.  
? When the temperature contrast is maximum, jet stream flows in near 
straight path. But when temperature contrast reduces, the jet stream 
starts to follow a meandering path. 
? So meandering depends on temperature contrast (temperature 
gradient).A meander is called peak or ridge if it is towards poles and 
trough if it is towards equator. 
? The meandering jet streams are called Rossby Waves. The existence 
of these waves explains the low-pressure cells (cyclones) and high-
pressure cells (anticyclones). 
? Jet streams flow just below the Tropopause. 
? Polar jet streams flow 6 – 9 km above the ground and Sub-tropical jet 
streams flows 10 – 16 km above the grounds. 
 
PERMANENT  JET STREAMS  
1. POLAR FRONT JET STREAMS  
? Polar front jet streams are formed above the convergence zone 
(40-60° latitude) of the surface polar cold air mass and sub-
tropical warm air mass.  The thermal gradient is steepened 
because of convergence of two contrasting air masses.  
? This jet stream was discovered by Rossby and also known as the 
primary jet stream. 
? It has an average speed of 215km/hour and in some cases, the 
speed may become double of the average speed. 
? They have an important role in the management of latitudinal 
heat budget of the earth and it accomplishes it through the 
creation of various cyclones and anticyclones in the Middle-
Latitude. 
 
? It plays a very important role in the distribution of precipitation 
in the middle latitude. 
? Cyclogenesis in the Temperate region is associated with the crest 
of Polar Front jet and maximum cyclonic rainfall occurs ahead 
of the trough. 
? At the same time, these jets also determine the path and 
movement of Temperate Cyclone. 
2.  SUBTROPICAL WESTERLY JET STREAMS  
? Subtropical westerly jet streams move in polar the upper 
troposphere to the north of subtropical surface high pressure 
belt (at jet stream the poleward limit of the Hadley cell in both 
the hemispheres) i.e above 30Q-35() latitudes.  
? It plays an important role in the distribution of precipitation over the 
subtropical latitude. 
? It has a major role in bringing western disturbances to India during 
the winter season and thus provides crucial rainfall which is vital for 
Rabi Crop. 
? The trough of the subtropical jet stream experiences high pressure 
and thus associated with the Tropical Deserts; and below the crest, 
the low-pressure system (cyclogenesis) may develop. 
 
LOCAL JET STREAMS: 
1. TROPICAL EASTERLY JET STREAMS  
o Tropical easterly jet streams develop in the upper troposphere 
above surface easterly trade winds over India and Africa during 
summer season due to intense heating of Tibetan plateau and 
play important role in the mechanism of Indian monsoon. 
o It originates due to excessive heating of Tibetan Plateau during 
the summer season due to which low pressure(converging) sets 
 
up at the surface and relatively higher pressure(diverging) in the 
upper troposphere. The part of this southward diverging air 
comes under the impact of Coriolis effect and it is forced to 
deflect from east to west leading to the formation of a tropical 
Jetstream. 
? One of the divergent limbs of Tropical Easterly Jetstream falls over 
the North -East India and which due to Coriolis deflection becomes 
Easterly. 
? TEJ steers the low-pressure depression found over the Bay of Bengal 
into the Indian Subcontinent. Due to this, much of the rainfall is 
received in the Indo-Gangetic Plain and Central India. 
2. SOMALIAN JET STREAM 
? Formed due to the unequal heating of continent of Africa and 
located at a very low height of 3-4 km, since the warm air above 
the Mozambique Channel produces a horizontal thermal 
contrast with the cold air from the African Highlands. 
? It also crosses the equator and becomes south-westerly in 
direction and due to this reason, it is known as Cross Equatorial 
Jet Stream. 
? Helps in the intensification of S-W Monsoon over Indian 
Subcontinent.