I received an email the other day asking about El Niño and what effect it might have on our part of the world, should one develop. For quite a while now the Pacific has been in a neutral El Niño Southern Oscillation (ENSO) phase, but there is some mention of an El Niño event possibly forming some time this summer. Here is a summary of the current El Niño forecast put out by the National Oceanic and Atmospheric Administration (NOAA).
Nearly all model forecasts indicate the persistence of ENSO-neutral conditions throughout the Northern Hemisphere for spring 2014, but afterward, an increasing number of models suggest the possible onset of El Niño. Strong surface westerly winds in the western Pacific, and the slight eastward shift of above-average temperatures in the subsurface western Pacific, potentially signify warming in the coming months. However, spring is also historically associated with lower forecast skill, so the chance of an El Niño event developing after the spring is not that likely.
Before I go into what effect this might have on us, I figured it has been several years since I’ve looked at this topic, so I think a bit of a lesson in El Niño is in order — I guess it’s the teacher in me.
Just what is EL Niño and why can it have such a profound impact on our weather? Well, to put it simply, El Niño is a change in ocean surface temperatures across the tropical and subtropical Pacific Ocean. This change in ocean temperatures then creates a change in the weather patterns across the Pacific Ocean. Now the big question is, why does a change in weather over the Pacific Ocean have any impact on us?
The first and most simple reason is that the Pacific Ocean just happens to cover half of our planet, so any large-scale change in it is bound to have an impact elsewhere. Actually, maybe it’s not that simple. Even though the Pacific Ocean is huge, why should changes in weather in that area of the world impact us? Keeping in mind just how big the Pacific is, let’s now look at what the Pacific Ocean is made of: water. Lots and lots of water.
That still doesn’t explain why changes in it affect the weather way over here. To really understand why, we need to remember it takes a whole lot of energy to warm up water, and conversely, water releases a whole lot of energy when it cools. In essence, water is like a battery that stores heat — therefore, the Pacific is a really big heat battery.
From a general point of view, weather is the atmosphere’s attempt to equal out heat imbalances. You see, just like most of us, the atmosphere likes things to be equal. If there is too much heat in one place or too much cold in another, the atmosphere tries to make things equal by sending cold air southward and warm air northward. The tropical areas of our planet rarely, if ever, see or feel the cold air trying to move southward. If you live in the Arctic regions, you would rarely, if ever, see the really warm air try to move northward. Those of us in the middle are constantly feeling and seeing this movement of cold and warm air — and we call it weather.
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Now, back to the Pacific Ocean, our big heat battery. If the Pacific is storing heat and releasing it into the atmosphere, that heat energy has to go somewhere. Some of it simply warms the air, but then the atmosphere wants to equal out that warm air, so off that warm air goes. A big chunk of the heat energy coming out of the Pacific goes into developing clouds, precipitation and storm systems. These storm systems are an efficient way for the atmosphere to move heat around and equalize it, because you can move a lot more energy by moving warm water around (remember, clouds are made up of water) than you can by moving warm air.
This overall movement of warm air and storm systems over the Pacific Ocean creates a general pattern of winds around the world. If you remember back to our articles about general atmospheric circulation, we know the general movement of air around the planet comes about by the Earth trying to equal out warm and cold regions — and this creates the westerly winds in our region of the world, the tropical easterlies to our south and, finally, the polar easterlies in the high Arctic.
Under normal temperature conditions across the Pacific, the general flow of the atmosphere follows this simple pattern, and since a large portion of our weather comes off the Pacific (because we live in the generally westerly flowing part of the atmosphere) our weather tends to be rather average. If we change the amount of heat over a large portion of the Pacific, either by warming up the Pacific Ocean (El Niño) or cooling it down (La Niña), this disrupts the general flow of air across this region and can start to impact how air flows across our region.
Next issue we’ll take a closer look at exactly what happens over the Pacific to allow El Niño to form, and examine how these events are classified.