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El Nino | La Nina |SO| ENSO| IOD-Indian Ocean Dipole| Factors affecting Indian Monsoon.| UPSC geography optional paper 2 2019

Why is the Indian Monsoon Erratic in Nature? Explain
(UPSC geography optional paper 2 2019, 10 Marks)


Table of Content

  • El Nino
  • Na Nina
  • Oceanic Nino Index( ONI)
  • Southern Oscillation( SO)
  • SOI- Southern Oscillation Index
  • ENSO-El Nino Southern Oscillation
  • India Ocean Dipole-IOD
  • Effect of these in Indian Monsoon

The Southwest Pacific margin ( Peruvian Coast) is warmer more than 0.5 degrees centigrade than the then southeast Pacific margin( Australian Coast), this situation is called El -Nino. It is about a 3-month session.

Opposite the El Nino ocean situation is called La-Nina. In La-Nina, the Peruvian coast is cooler compared to normal ocean temperature.
El Nino and La Nina
El Nino and La Nina

Oceanic Nino Index( ONI):
ONI=Surface Temperature of the pacific ocean along with northwestern South America- Surface Temperature of the pacific ocean along with  North-East Australia, Indonesia, and the Philippines.
If ONI is greater 0.5
      than strong EL-Nino
else if ONI is between 0.1 to 0.5
    weak El-Nino
else if ONI is less than 0
   than Na-Nina or normal year

Southern Oscillation ( SO):
Gilbert Walker British Mathematician discovered the southern oscillation; a large-scale change in sea level atmospheric pressure across Indonesia and the tropic of the Pacific.
Many global climates including monsoon is a correlation with SO.

Southern oscillation index ( SOI):
It gives the intensity of El Nino and LA Nino.
SOI=atmospheric pressure of Tahiti( South Pacific ocean)-atmospheric pressure of Darwin( Australia)
If SOI is positive
   LA Nina
    El Nino

ENSO( El Nino southern oscillation):
  • ENSO refers to the oscillation between EL Nino and LA Nina alternatively.
  • Changes in Ocean temperature and atmospheric pressure are connected to each other; together concept is called ENSO.

Effect of ENSO:

  • Each phase triggers predictable disruption of temperature, precipitation, and wind leading to cascading effects at the global level atmospheric circular such as monsoon.
  • Flood in Peru, Ecuador, Mexico, USA.
  • Drought in Australia, India, and southern Africa.
Effect of EL-Nino and ENSO on Indian Monsoon:

  • Scientists and researchers found no direct correlation between ENSO and Monsoon but by observation, it is found that:
  • All LA Nina years, above than normal monsoon;
  • Not all El Nino but most of it resulted in normal Monsoon.
  • From 1997 -to 98; El Nino strong but above average monsoon in India.
  • In 2002; although week El Nino observed but high drought in India.
IOD-Indian Ocean Dipole:

  • It is referred to as a swing in sea surface temperature in the western and eastern Indian ocean, which is known as Indian Ocean Dipole.
  • Positive IOD can cater to EL-Nino Effect
  • Weak IOD negatively affects the monsoon.
  • Warming up of the west Indian ocean boosts monsoon rain.
  • IOD number = temperature of the Arabian sea - the temperature of the eastern Indian ocean at the Indonesian coast.
  • If IOD is greater than 0
  •      Good monsoon
  • Else
  •     Below average monsoon.

Factors affecting Indian Monsoon:

  • EL-Nino
  • Na-Nina
  • ENSO
  • IOD
  • Heating of  Tibetan Plateau from April to June month
  • Himalayan and Eurasian snow cover.
    • Less snow cover means warmer subcontinent will bring more rain.
  • Tropical Easterly Jet
  • Presence of High-pressure areas in the Madagascar region
Try to solve the following questions:
  • Discuss the major characteristics of the Indian monsoon with special emphasis on the causative factors( UPSC 1922)
  • Discuss the recent theories put forward to explain the origin and mechanism of the Indian Monsoon. ( UPSC, 1994)
  • Elucidate the mechanism of the Indian Monsoon( UPSC, 1999)
  • Explain the Origin, Mechanism, and characteristics of the Summer Monsoon in India. ( UPSC 2002)
  • Give a Critical account of the recent theories of the origin of the Indian monsoon with special reference to the Jet Stream Theory. (UPSC, 2006)
  • Discuss the mechanism and origin of Monsoon winds and explain the role of El Nino on Monsoon circulation. ( UPSC, 2008)
  • Discuss the mechanism of the Indian Monsoon (UPSC 2013)
  • Discuss the nature and origin of the Indian monsoon and recent techniques for its prediction. ( UPSC, 2014)
  • Give a reasonable account of the Unusual Pattern of Distribution of Monsoonal rainfall in India. ( UPSC, 2017)
  • Why is the monsoon erratic in nature? Explain. ( UPSC 2019)
  • Explain the origin, progress, and retreat of the Indian monsoon and discuss its impact on the Indian economy. (UPSC 2018, 250 words, 20 marks)
  • Elaborate on the origin of monsoon with reference to thermal and recent concepts. ( UPPSC 2020)

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3 August 2021 at 22:33 ×

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