La Nina - Abnormally strong upwelling conditions along the Pacific coast of South America extend cool waters westward and create disruptions of the entire oceanic-atmospheric system in the tropical and equatorial pacific. Because the ocean and atmosphere are linked, this abnormal cooling results in a change in the distribution of rainfall on land, heat flow in the oceans, atmospheric patterns, upwelling events and regional storm activity, often in ways opposite to El Nino.

Non-El Nino - Sometimes called La Nina, or Old Viejo.

Upwelling - North-blowing winds along the Pacific South American coast force surface waters into motion. The Coriolis Effect, a consequence of the earth spinning, deflects the water ninety degrees to the left of the wind direction so that it moves off shore at right angles to the coast. This water is replaced from below in conveyor-belt fashion. Typically upwelling in this region brings to the surface cool, nutrient-rich waters from below the thermocline. This input stimulates tremendous primary productivity that supports extensive communities and food webs. Upwelling still occurs during El Nino events but the thermocline is pushed too deep for this mechanism to tap into these productive waters and bring them into the photic zone. As a consequence, biological interactions fall apart as the base of the energy pyramid, namely phytoplankton, starve for essential materials to grow and reproduce.

Thermocline - An abrupt and dramatic temperature gradient that marks the transition between warm surface waters and the cooler waters below. Its depth is very important in the discussion of El Nino. The ability of longshore winds to create upwelling events conducive to high productivity is dependent upon the depth of the warm surface layer. If it is too thick, upwelling will serve to only cycle the warm water and the enriched water found below the thermocline will never reach the photic zone.

Photic Zone - The three-dimensional layer of water that receives sufficient solar radiation such that photosynthesis can occur. In the ocean this zone of primary production can be over 100 meters thick.