Causes and effects El Nino and La Nina.

What is El Niño? A shift in the water flow in the Pacific Ocean. This happens near the west coast of South America every few years, where the cool water normally present becomes blocked by warmer water, and causes drastic changes in the weather in the Americas and perhaps the rest of the world. The effects El Nino has on places ranges from warmer, colder or even drought.

Named El Niño, which literally means "the boy", this environmental event typically starts during or near the Christmas Season, a tradition intended to celebrate the birth of a specific boy. A probable reason for the name.

Whereas El Nino occurs when the water warmer than normal, the opposite can happen too. We call an unusually cold spell of sea surface temperatures in the Pacific "La Niña". La Nina (the girl) causes warm, cold, wet and drought in different parts of the world instead.

What is the cause?

We begin with the Walker Circulation. The ocean currents and atmospheric winds interact with each other in complicated, mysterious ways. Convection examples of this type include the zonal mixing in equatorial regions of the Pacific Ocean maps, affecting the large scale tropical cell of convection known as the Hadley circulation.

This cell forms a pair of loops stretching from the equator and overturning around 30 degrees pole ward, resulting in the stormy inter tropical convergence zone (ITCZ) and the horse latitude areas (characterized by dry and calm conditions).

Anyway, this cell is not perfect, and some asymmetry appears, then east-west cells can develop in addition. The one over the Pacific gets the name Walker circulation after its discoverer.

Because of this cell, winds normally blow from the east from South America onto the ocean surface, sweeping the warmer water westward and allowing cooler water to emerge from below.

Occasionally this thing hiccups. Officially, we call this change the Southern Oscillation. We can even see portions of this convection reverse direction. When this happens once every two to five years (usually), the winds blow the surface water eastward and warm sea water lies off the coast of Peru and Ecuador, where the people named it El Niño.

Anyway, it is not only these warm waters, but the whole reversal which causes the effects El Nino gives and climactic disruptions we experience. Consequently, scientists refer to the whole system as ENSO (El Niño - Southern Oscillation).