A lot of people probably struggle with the terms La Nina, and El Nino. Though you would hear them through the media all the time, a majority of people dont understand how the phenomenons work
Very simply, La Nina is cooler water across the Equatorial Pacific Basin, El Nino is warmer water across the Equatorial Pacific Basin. There are many reasons why this occurs, and will require to much depth and detail to go into it here.
Heres an example of what Sea Surface temperatures look like during a La Nina.
Very cold water, up to 3 degrees below normal, covers the equatorial pacific coming out of South America. Warm water stacks up against the Australian East coast, which is why we usually receive extreme rainfall.
The opposite is El nino, which can be seen here.
Much cooler water around Australia’s East coast, but this is not the reason for little rainfall and droughts. The main reason is the Walker circulation is reversed. Usually, trade winds come from the East from South America, which means cool water from beneath rises to the surface on the South American coast. This is known as upwelling. This cool water travels East through the Pacific basin. It also means the Easterly trade winds push all the moisture over Australia.
In An El nino, surface currents of the ocean, and the air above it, reverse. So we have westerly winds develop and push the warmer water back towards South America, net effect being that no moisture is pushed over Australia, instead out into the Pacific.
Heres a good graphic showing this.
Also notice the graphic underneath both pictures, showing the thermocline, which is a simple way of looking at the ocean from a side on view.
Something like this.
In a La nina, the thermocline slope is high. In an El nino, the thermocline slope is low as the warm water pushes the cold water down to the depths. In a neutral year, the slope is relatively high but neither here nor there.
So why all this you ask? Well, because soon i will show current conditions and what to expect for the coming season. Both phenomenon run from about October through to March, if its neither it becomes neutral, which means normal weather basically.