For Katrina: Tell Me About El Nino and La Nina

Katrina asked: Explain the difference between El Nino and El Nina and how are they different within each region of the USA?

Pretend I have ~ on top of the n's throughout, would you? El Nino and La Nina represent two aspects of the same phenomena, an oscillation in the Pacific Ocean characterized by pressure differences between Darwin, Australia and Tahiti and surface water cooling or heating in the Central and Eastern Pacific. It affects both the atmosphere and the ocean, and, to date, no one has entirely pinned down why it happens.

The aren't really two different things, but the same thing. It's called El Nino when the temperature goes up, the warm phase of the oscillation. It's called La Nina when the temperature drops, the cool phase of the oscillation. Although it is a periodic oscillation, it does not have a regular period and tends to manifest every two to seven years.

So what? Well, these heating and cooling patterns can have a profound effect on tropical storms, rainfall, and drought all around the rim of the Pacific. However, the effects are seen all over the world as a corresponding effect on Atlantic often occurs 12-18 months after the Pacific anomaly. The normal trade winds slow or flow backwards and other currents and weather patterns are disrupted.

In general and most directly, El Nino makes the Southern portion of the East Pacific wetter and warmer and the Northern and Western Pacific colder and dryer, as well as sending tropical storms in different directions, but there can be effects on Europe as well, and the number of Atlantic tropical storms is reduced because of wind shear. Fishing, as currents are disrupted and water temperatures (and nutrients) are anomalous, can be severely impacted.

For La Nina, the effects are kind of opposite. Where El Nino makes it dryer, La Nina makes it wetter and vice versa. I've included some graphical representations of the effects for the interested.