2. MONSOON
• Monsoon is a complex meteorological and
atmospheric circulation phenomenon.
• Earlier, it was considered to be a simple
atmospheric circulation
• But over a period of time experts through
researches at various levels try to prove this
complex phenomenon more accurately.
4. THERMAL THEORY
• This classical theory of Indian monsoon proposed and
put forth by Admand Hally in 1686
• Monsoonal winds are land and sea breezes produced
by unequal and differential heating of continental and
oceanic areas.
5. NORTH EAST MONSOON
• During the northern winter when sun rays fall vertically
over tropic of Capricorn the land mass of Asia cools
rapidly than the ocean generating a high pressure area
over Asia while there is low pressure Centre on the Indian
ocean.
• As a result of this there is an out flow of air from high
pressure to low pressure, consequently the surface winds
started to flow from land to sea.
• This wind pattern is commonly known as north-east
monsoon
• Often dry due to lack of moisture and hence do not
precipitate.
6. SOUTH WEST MONSOON
• During the northern summer season sun rays fall vertical on
tropic of Cancer
• Due to excess heating of huge land mass of Asia a low
pressure area develop over it. Conversely, high pressure
Centre is developed in the Indian Ocean due comparative
low thermal conditions.
• As a result of this winds started flowing from high pressure
area over ocean to low pressure area over Indian
subcontinent.
• This pattern of wind flow is popularly known as southwest
monsoon in India.
• Due to on shore nature of southwest monsoon it bears and
produces rainfall wherever it is obstructed by various
topographical barriers.
7. DISADVANTAGES
• The thermal and classical theory proposed got wide
popularity and support of the scholars throughout the
world due its simplicity to explain the Indian
monsoon.
• This concept fails the explanations of onset, breaks
and spatial distribution of rainfall over the Indian
subcontinent.
8. JET STREAM THEORY
• The jet streams are a narrow belt of high
altitude westerly winds in the troposphere
• It’s speed varies from about 110km/h in
summer to about 184 km/h in winter.
• The main types are the polar jets, the
subtropical westerly jets and the less common
tropical easterly jets.
10. TIBETIAN PLATEAU
• It is located in a altitude
of 5000 meters
• It spread over about 2
lakh square kilometers.
• The Tibet plateau act as
a heat engine .
11. ROLE OF TIBETIAN PLATEAU
• It acts as a mechanical barrier for subtropical
westerly jet stream to completely withdraw from
India which helps burst of Indian monsoon.
• It produces a thermal anticyclone in mid
troposphere over this region. This anticyclone
weakens the western subtropical jet stream to the
south of Himalayas but produces tropical easterly
jet on the southern side of the anticyclone
12. SOUTH WEST MONSOON
• The high temperature over the Tibetan Plateau, as well
as over Central Asia in general, during the summer
leads to the formation of the tropical easterly jet over
India in summer.
• This tropical jets first develop in longitudes east of
India and then extends westward across India, over the
Arabian Sea and to eastern Africa.
• Air under this jet stream blowing along Kolkata-
Bangalore axis, the air descends over Indian Ocean and
southwest monsoon moves towards Indian
subcontinent.
13. CONTD…
• The onset of SW Monsoon is driven by the shift of the
subtropical westerly jet northwards towards the Tibetan
Plateau.
• As the Tibetan Plateau heats up, the low pressure created
over it pulls the westerly jet northwards.
• The westerly jet is inhibited from moving northwards by
Himalayas.
• However, with continuous heating, sufficient force for the
movement of the westerly jet across the Himalayas is
created at a significant level.
• As such, the shift of the jet is sudden and abrupt causing the
bursting of SW Monsoon rains onto the Indian plains.
14. NORTH EAST MONSOON
• The westerly jet causes high pressure over
northern parts of the subcontinent during the
winter. This results in the north to south flow
of the winds in the form of the NE Monsoon.
15. Ocean Bodies and Air Circulations
• El Nino- It is a narrow warm current which appears off the
coast of Peru in December. when the surface temperature goes
up in the southern Pacific Ocean, India receives deficient
rainfall.
• Southern Oscillation- It is a curious phenomena of sea-
saw pattern of meteorological changes observed between the
Pacific and Indian oceans.
16. REFERENCE
• Concept, Mechanism and Behaviour of Indian
Monsoon. Pawan Kumar. SHRINKHALA : VOL-II *
ISSUE-II*October-2014
• www.imd.gov.in
