El Nino | La Nina | ENSO | Indian Ocean Dipole

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  • El Nino word stands for “Blessed Child” or “Christ Child”.
  • It occurs every 2-7 years.
  • Causes catastrophic floods in Peru & other Central American regions, tornadoes in North America along with draughts & forest fires in Indian Subcontinent & Australia.


  • Peruvian Coasts generally have Cold Peruvian Currents which are upwelling zones & very good for the fishing industry.
  • Unexpected warm surface current is seen on the Peruvian coast during an El Nino year.
  • Trade Winds blowing from East to West is weakened. Hence, the warm surface water is not transferred to the Australian Coast as done normally by Trade Winds.
  • Upwelling Zone at Peru is weakened.
  • Low Pressure established at Peruvian Coast due to warm surface water.
  • This Low Pressure leads to rising of moisture & formation of clouds & hence, heavy rainfall along with catastrophic floods in Peru which normally is very dry.
  • This Low Pressure at Peru weakens the Low Pressure in North India as the High Pressure near Madagascar has another Low Pressure available to divert it’s moisture-laden winds. Hence, Indian Subcontinent receives lesser than average rainfall during El Nino years leading to drought-like situations & forest fires.
  • Australia also sees drought & forest fires in El Nino.
El Nino

El Nino


  • La Nina is nothing but, the re-strengthening of normal conditions.
  • It is the opposite of El Nino.
  • Peruvian Coast again sees Cold Currents.
  • India & Eastern Australia again see good monsoon rainfall.


  • ENSO is El Nino Southern Oscillations
  • It is simply EL NINO + LA NINA
  • The complete process of El Nino * La Nina is collectively known as ENSO


  • The Walker circulation is seen at the surface as easterly trade winds which move water and air warmed by the sun towards the west.
  • The western side of the equatorial Pacific is characterised by warm, wet low-pressure weather as the collected moisture is dumped in the form of typhoons and thunderstorms.
  • The ocean is some 60 cm higher in the western Pacific as the result of this motion.
  • The water and air are returned to the east. Both are now much cooler, and the air is much drier.
  • An El Niño episode is characterised by a breakdown of this water and air cycle, resulting in relatively warm water and moist air in the eastern Pacific.


  • The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.
  • The IOD involves an aperiodic oscillation of sea-surface temperatures, between “positive”, “neutral” and “negative” phases.
  • A positive phase sees greater-than-average sea-surface temperatures and greater precipitation in the western Indian Ocean region, with a corresponding cooling of waters in the eastern Indian Ocean—which tends to cause droughts in adjacent land areas of Indonesia and Australia.
IOD Positive

IOD Positive

  • The negative phase of the IOD brings about the opposite conditions, with warmer water and greater precipitation in the eastern Indian Ocean, and cooler and drier conditions in the west.
IOD Negative

IOD Negative


  • Floods in South America
  • Droughts in India & Australia
  • Severe impact on the Fishing Industry of Peru.
  • Severe impact on Agriculture Industry of India.
  • Severe impact on the survival of Coral Reefs (Coral Bleaching).
  • Food Inflation in India.
  • MSP issue (impact on Budget Deficit of Government)
  • Impacts on Livelihood of BPL members & farmers.

Course Discussion