Topic: El Niño
Theme: Change

Key Concepts:

Weather Patterns

  • El Niño alters normal patterns of atmospheric convection in the Pacific.
  • The displacement of the intertropical Convergence Zone eastward influences where rain clouds form, and, consequently, alters the typical atmospheric subtropical jet stream pattern around the world.
  • During a normal year, there is an area of high pressure located over the central, cooler portion of the Pacific, near South America. Also, there is an area of low pressure located over the western, warmer portion of the Pacific, near Indonesia. Low pressure areas experience greater amounts of rainfall.
  • During an El Niño year, the pressure levels change. The convection cell shifts and moves toward the central tropical Pacific. Areas that normally have rain now experience droughts. Australia faces drought (which ruins crops) and raging wildfires (that are usually drenched by the normal rainfall). Areas that normally are dry now experience an excessive amount of rain. The rain reaches as far east as Peru, which is normally very dry.


  • During an El Niño, the thermocline in the eastern Pacific deepens as the Kelvin waves carry warm water with along the equator. This process thickens the warm upper ocean layer in the eastern portion of the Pacific, but the depth of the thermocline decreases in the western Pacific.


  • The coastal and equatorial waters off of Peru are normally regions where cold, nutrient-rich water from below is upwelled to the surface layer.
  • As the warm pool of water comes across the equatorial Pacific, it displaces the once cool surface water. The less dense warmer water causes stable stratification (meaning there is a consistancy throughout the layering because little mixing occurs) of the water column. Upwelling continues, but it brings up warm water, not cold water.