PPT: Role of Jet Stream | Geography for UPSC CSE PDF Download

 Page 1


Indian 
Monsoon 
Mechanism 
and the Role of 
Sub Tropical 
Jet Streams
? The burst of monsoons depends upon the 
upper air circulation which is dominated by Sub 
Tropical Jet Streams (STJ).
? The south west monsoon coming in India is 
related to tropical easterly stream. It blows 
between 8 degree- 35 degree North latitudes.
? The north east monsoon (winter monsoon) is 
related to the subtropical westerly Jet Stream 
which blows between 20 degree and 35 degree 
latitudes in both hemispheres.
Page 2


Indian 
Monsoon 
Mechanism 
and the Role of 
Sub Tropical 
Jet Streams
? The burst of monsoons depends upon the 
upper air circulation which is dominated by Sub 
Tropical Jet Streams (STJ).
? The south west monsoon coming in India is 
related to tropical easterly stream. It blows 
between 8 degree- 35 degree North latitudes.
? The north east monsoon (winter monsoon) is 
related to the subtropical westerly Jet Stream 
which blows between 20 degree and 35 degree 
latitudes in both hemispheres.
Seasonal 
Migration of 
STJ
? In winter, STJ flows along the southern slopes of the 
Himalaya and in summer shifts northwards 
dramatically, flowing along the edge of Himalayas in 
early June and in late summer (July-August) along the 
northern edge of the Tibetan Plateau.
? The periodic movement of the Jet Stream often 
indicates the onset and subsequent withdrawal (STJ 
returns back to its position – south of Himalayas) of the 
monsoon.
? Northward movement of the subtropical jet is the first 
indication of the onset of the monsoon over India.
Page 3


Indian 
Monsoon 
Mechanism 
and the Role of 
Sub Tropical 
Jet Streams
? The burst of monsoons depends upon the 
upper air circulation which is dominated by Sub 
Tropical Jet Streams (STJ).
? The south west monsoon coming in India is 
related to tropical easterly stream. It blows 
between 8 degree- 35 degree North latitudes.
? The north east monsoon (winter monsoon) is 
related to the subtropical westerly Jet Stream 
which blows between 20 degree and 35 degree 
latitudes in both hemispheres.
Seasonal 
Migration of 
STJ
? In winter, STJ flows along the southern slopes of the 
Himalaya and in summer shifts northwards 
dramatically, flowing along the edge of Himalayas in 
early June and in late summer (July-August) along the 
northern edge of the Tibetan Plateau.
? The periodic movement of the Jet Stream often 
indicates the onset and subsequent withdrawal (STJ 
returns back to its position – south of Himalayas) of the 
monsoon.
? Northward movement of the subtropical jet is the first 
indication of the onset of the monsoon over India.
STJ in Summer
? With the beginning of summer, the STJ [upper westerlies] start 
their northward march.
? The weather over northern India becomes hot, dry and squally due 
to larger incoming solar radiation and hot winds like loo.
? Over India, the Equatorial Trough (ITCZ) moves northwards with 
the weakening of the STJ south of Tibet, but the burst of the 
monsoon does not take place until the upperair circulation has 
switched to its summer pattern.
? By the end of May the southern jet breaks and later it is diverted 
to the north of Tibet Plateau. There is sudden onset of monsoons 
(the ridge moves northwards into Central Asia, the high pressure 
zone over north-west India moves northwards into Central Asia 
making way for south-west monsoon winds)
Page 4


Indian 
Monsoon 
Mechanism 
and the Role of 
Sub Tropical 
Jet Streams
? The burst of monsoons depends upon the 
upper air circulation which is dominated by Sub 
Tropical Jet Streams (STJ).
? The south west monsoon coming in India is 
related to tropical easterly stream. It blows 
between 8 degree- 35 degree North latitudes.
? The north east monsoon (winter monsoon) is 
related to the subtropical westerly Jet Stream 
which blows between 20 degree and 35 degree 
latitudes in both hemispheres.
Seasonal 
Migration of 
STJ
? In winter, STJ flows along the southern slopes of the 
Himalaya and in summer shifts northwards 
dramatically, flowing along the edge of Himalayas in 
early June and in late summer (July-August) along the 
northern edge of the Tibetan Plateau.
? The periodic movement of the Jet Stream often 
indicates the onset and subsequent withdrawal (STJ 
returns back to its position – south of Himalayas) of the 
monsoon.
? Northward movement of the subtropical jet is the first 
indication of the onset of the monsoon over India.
STJ in Summer
? With the beginning of summer, the STJ [upper westerlies] start 
their northward march.
? The weather over northern India becomes hot, dry and squally due 
to larger incoming solar radiation and hot winds like loo.
? Over India, the Equatorial Trough (ITCZ) moves northwards with 
the weakening of the STJ south of Tibet, but the burst of the 
monsoon does not take place until the upperair circulation has 
switched to its summer pattern.
? By the end of May the southern jet breaks and later it is diverted 
to the north of Tibet Plateau. There is sudden onset of monsoons 
(the ridge moves northwards into Central Asia, the high pressure 
zone over north-west India moves northwards into Central Asia 
making way for south-west monsoon winds)
Why no 
south-west 
monsoons in 
March – May 
(summer)?
? During the summer season in the Northern Hemisphere, low 
pressure areas develop at the ground surface near Peshawar 
(Pakistan) and north-west India due to intense heating of ground 
surface during April, May, and June.
? As long as the position of the upper air jet stream is maintained 
above the surface low pressure (to the south of Himalayas), the 
dynamic anti-cyclonic conditions persist over north-west India.
? The winds descending from the upper air high pressure [because 
of the ridge of STJ] obstructs the ascent of winds from the surface 
low pressure areas, with the result that the weather remains warm 
and dry.
? This is why the months of April and May are generally dry and 
rainless in spite of high temperatures (low pressure on land) and 
high evaporation.
Page 5


Indian 
Monsoon 
Mechanism 
and the Role of 
Sub Tropical 
Jet Streams
? The burst of monsoons depends upon the 
upper air circulation which is dominated by Sub 
Tropical Jet Streams (STJ).
? The south west monsoon coming in India is 
related to tropical easterly stream. It blows 
between 8 degree- 35 degree North latitudes.
? The north east monsoon (winter monsoon) is 
related to the subtropical westerly Jet Stream 
which blows between 20 degree and 35 degree 
latitudes in both hemispheres.
Seasonal 
Migration of 
STJ
? In winter, STJ flows along the southern slopes of the 
Himalaya and in summer shifts northwards 
dramatically, flowing along the edge of Himalayas in 
early June and in late summer (July-August) along the 
northern edge of the Tibetan Plateau.
? The periodic movement of the Jet Stream often 
indicates the onset and subsequent withdrawal (STJ 
returns back to its position – south of Himalayas) of the 
monsoon.
? Northward movement of the subtropical jet is the first 
indication of the onset of the monsoon over India.
STJ in Summer
? With the beginning of summer, the STJ [upper westerlies] start 
their northward march.
? The weather over northern India becomes hot, dry and squally due 
to larger incoming solar radiation and hot winds like loo.
? Over India, the Equatorial Trough (ITCZ) moves northwards with 
the weakening of the STJ south of Tibet, but the burst of the 
monsoon does not take place until the upperair circulation has 
switched to its summer pattern.
? By the end of May the southern jet breaks and later it is diverted 
to the north of Tibet Plateau. There is sudden onset of monsoons 
(the ridge moves northwards into Central Asia, the high pressure 
zone over north-west India moves northwards into Central Asia 
making way for south-west monsoon winds)
Why no 
south-west 
monsoons in 
March – May 
(summer)?
? During the summer season in the Northern Hemisphere, low 
pressure areas develop at the ground surface near Peshawar 
(Pakistan) and north-west India due to intense heating of ground 
surface during April, May, and June.
? As long as the position of the upper air jet stream is maintained 
above the surface low pressure (to the south of Himalayas), the 
dynamic anti-cyclonic conditions persist over north-west India.
? The winds descending from the upper air high pressure [because 
of the ridge of STJ] obstructs the ascent of winds from the surface 
low pressure areas, with the result that the weather remains warm 
and dry.
? This is why the months of April and May are generally dry and 
rainless in spite of high temperatures (low pressure on land) and 
high evaporation.
Western 
Disturbances
? Western Disturbances develop in the mid latitude region (north 
of the Tropic of Cancer), not in the tropical region, therefore they 
are called as mid latitude storms
? Western Disturbances are low pressure systems, embedded in 
western winds (westerlies) that flow from west to the east.