JET STREAMS AND INDIAN MONSOON
ORIGIN OF JET STREAM:
- The term was introduced in 1947 by Swedish-born US meteorologist Carl-Gustaf Rossby
- It is used to describe a very strong westerly wind blowing at a higher altitude just below the Tropopause.
- The highest streams occur during winter
SALIENT FEATURES OF JET STREAMS:
- They generally circulate both the hemisphere so they are called Circumpolar winds
- Since they are higher altitude wind they are estimated to blow at 6-14 km height
- They are called as High-Altitude Westerly Wind system
- These streams are formed due to the difference in Temperature
- They shift along with Sun's movements
- Formation of Rossby waves (when the sun move towards the south there develops waves at the polar front jet stream which are called Rossby waves)
TYPES OF JET STREAMS
- Polar Front Jet Stream
They are commonly irregular in their location and are discontinuous
It originates above the Subpolar Low-Pressure Belt
It freezes Canada and parts of the U.S
- Sub Tropical Jet Stream
They usually lie between 20°and 30°latitudes, North and South
It originates above Subtropical High-Pressure Belt
They are responsible for the sudden burst of the Indian Monsoon
- Tropical Easterly Jet Stream
Intense heating of Tibetan plateau which intensifies Indian Monsoon
- Polar Night Jet Stream
They Develop in the winter season and height of 30m
High wind velocity during winter and their velocity decreases during summer
MONSOON:
- Derived from the Arabic word “Muslim" meaning season
SALIENT FEATURES OF INDIAN MONSOON:
- At least 120° reversal between 2 seasons
- High Pressure and Low pressure should interchanges
- Sudden Burst of Monsoon
- Influence of mountains
- Uneven distribution of rainfall
- Tropical Cyclone influence
- Indian Agriculture is gambling of Monsoon
MONSOON MECHANISM:
- There are commonly two theories namely - Thermal and Dynamic
- Thermal Theory: Proposed by Sir.Edmund Halley stating that Differential heating of land and sea due to Temperature variations
- Dynamic Theory: Proposed by Flohn stating that shifting pressure belts according to the sun's movement
LAND AND SEA BREEZE:
- SEA BREEZE – When a region is hotter than the neighboring region the air from the cooler region moves into the hot region to take the place of the hot air which has expanded and risen. During the day the land gets warmer than the sea producing low pressure over the land into which cooler air moves from over the sea. Thus, the local wind that blows from sea to land during the day is called Sea Breeze.
- Sea breeze reaches maximum strength during the mid-afternoon when the temperature difference between the land and the sea is greater and dies out by evening as the sun's heat diminishes
- They are best developed in Tropics when conditions are calm and the sky is clear but can also be observed in temperate areas under certain conditions. They are greatly variable.
- The land gets High Temperature and low pressure and Sea gets low temperature and High pressure to land
- The above phenomenon makes the wind move Horizontally from the High-pressure region of the sea to the low-pressure region of land.
- LAND BREEZE - During the night the land cools more quickly than the sea and a reverse process sets in.
- Land breeze is a cool wind that blows from the land to the sea during the nighttime radiation cools the land and the air in contact with the ground surface.
- Land breeze is most common in tropical areas but also occurs in high latitudes particularly when the weather is calm.
- Land breeze is not as Strong as the Sea breeze
TYPES OF MONSOONS BASED ON HALLEY'S THEORY:
- Asian Monsoon: During Summer, Sun shifts to the Tropic of Cancer makes the Land part of Asia warmer than Sea, makes high Temperature and low pressure in Baikal Lake in the Pacific Ocean near Aleutian Islands Sea becomes cooler than land with high Pressure and low temperature in that Area. This makes the wind move from Aleutian highs toward Baikal low-pressure region.
- The process gets reversed in winter.
- South Asian Monsoon: They mark the season of transition between the hot rainy season and cold dry season. Characterized by humidity and oppressive heat known as ‘October Heat. The heat low is developed over southern Asia in the lower level of the atmosphere. From the Indian Ocean and the South-western Pacific warm, humid air moves northward and North Westward into Asia passing over India.
- This airflow accompanied by heavy rainfall constitutes the summer monsoon in Southeast Asia
Content Credits: Leo Srilekha
