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.
Thermocline
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.
Upwelling
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.
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