Over at Evolve Snow Camps, we talk about the fact that this year’s El Nino could reach a record high.
But what is actually happening in the oceans when we talk about the El Nino phenomenon?
An El Nino year is characterized by a year with warmer than average sea surface temperatures in the Pacific Ocean. This means that the temperature of the top layer of the Pacific Ocean, specifically around the equator, are a few degrees Celsius higher than normal.
These warmer temperatures affect the ocean and the atmosphere, especially inducing climate effects in the Northern Hemisphere. The warmer temperatures also move the fierce oceanic thunderstorms of the equator further eastward along their route.
Here’s how it all happens:
To replace the water that has drifted west, water is pulled upward from deeper levels of the eastern pacific. Since this water is coming from a deeper layer of the ocean, it is therefore much colder, lowering the surface temperature of the water.
On the year of an El Nino, the winds blowing westward are much weaker than they normally would be. This causes less water to drift westward, and consequently there is less water displaced in the east. For this reason, less cold water rises upwards in the east to replace the water that would have drifted west.
With less cold water flowing upward, surface temperatures do not cool as much as they normally would. The result is higher than average surface temperatures in the east.
In other words, the Pacific Ocean is warmer than normal – especially along the eastern part of the equator.
These warmer conditions affect the winds, lessening the strength of the gusts. The weaker winds work in a positive feedback loop, calling for even LESS water to drift west and temperatures in the east to therefore raise to EVEN warmer temperatures.
This loops finally ends after the El Nino year has passed. Eventually, a Kelvin wave (a massive wave which can reach hundreds of thousands of kilometres long in width, though not very high) travels in.
This type of wave changes into a Rossby wave, which is similar to a Kelvin however moving at a much slower speed. The Rossby wave can take months, or even years, to cross the ocean. This Rossby wavesthus carries cooler water in the eastern pacific and counteracts the effects of El Nino