ENSO Globally

• Normal conditions:

  • Trade winds blow Equator wise and westward across the tropical pacific
  • Wind blows towards warm water of western pacific
  • Convectional uplift occurs as water heats atm
  • Trade winds push warm air westwards. Along East coast of Peru, shallow position to pull up water from below
  • Causes upwelling of nutrient rich cold water = optimum fishing conditions
  • Pressure of trade winds causes sea levels in Australasia to be 50 cm higher than Peru
  • Walker loop returns air to eastern tropical pacific
• El Nino Year:

  • Trade winds in western pacific weaken and die [may even be a reverse direction of flow]
  • Piled up water in west moves back east so there is a 30 cm sea level rise in Peru
  • Region of rising air moves east with associated convectional lift. Upper air disturbances distort jet steams paths = teleconnections all around the world
  • East pacific ocean becomes 6 - 8 ℃ warmer. Overrides cold northbound Humboldt current so breaks food chain
  • Lack of phytoplankton = decrease in fish numbers so fish eating birds on Galapagos Islands affected
  • Conditions = calmer across whole pacific
• La Nina Year:

  • Extremely strong trade winds
  • Trade winds push warm water westwards giving a sea level up to 1 meter higher in Philippines and Indonesia
  • Low pressure develops with very strong convectional uplift as very warm water heats the atmosphere = heavy rain in south east Asia
  • Increase in equatorial undercurrent and very strong upwelling of cold water off Peru coast result in strong high pressure and extreme drought
  • Major problem in already semi-arid areas of north Chile and Peru
• Key Points: