By this point, most folks are aware of the drought that currently has California (and Texas, too, for that matter) in it’s grips (and if you haven’t heard, then check out our post The California Drought). What’s new to this story is the strengthening of El Niño in the Pacific. And while El Niño first manifests itself in the Equatorial Pacific Ocean, the effects of El Niño are felt worldwide, including drought stricken California.
But, wait, let’s back-up a bit. What’s El Niño (really)? Less than a year ago, I only had a vague notion about what it is (something about climate and departures from the norm and the Pacific; also fish, definitely something about fish). And then I entered a marine sciences department and took Physical Oceanography, where I learned all about climate cycles, including El Niño (the ‘official’ name is El Niño Southern Oscillation or EÑSO for short). Before you understand El Niño conditions, it’s first important to know the normal conditions (since El Niño is all about departures from normality).
NORMAL (not that anything is ever really ‘normal’):
1. There’s typically a warm pool of water that hangs out in the Western Pacific Ocean.
2. This warm pool heats the air above it, causing the surface air to rise.
3. The warm air enters the upper atmosphere and moves from the West Pacific to the East Pacific. By this point, the air has cooled and wants to sink back down to the sea surface.
4. This circulation causes the trade winds that are characteristic of the equatorial Pacific. The trade winds literally push water from the Eastern Pacific Ocean to the Western Pacific Ocean, causing a slight change in sea surface height (which has now been confirmed by using satellites to measure the height of the ocean).
5. The water now piling up in the Western Pacific has to go somewhere, and since it can’t go up, it must go down.
6. The water then travels from the Western Pacific Ocean to the Eastern Pacific Ocean where, in order to compensate for the sloping sea surface, moves from the deep ocean to the surface (called upwelling), bringing cold, nutrient rich water from the deep to the surface (and fuels the thriving fisheries industry off the coast of South America).
EL NIÑO (when things go awry….):
1. There’s something called the Julian-Madden Oscillation that can change the normal trade wind pattern and produce a westerly wind burst over the warm pool (assuming all the conditions are just right and the fate stars are perfectly aligned).
2. If this happens just right and at just the right time, this wind burst can set up a Kelvin Wave along the equatorial Pacific (literally a huge ‘wave’ in the water – though not a surface wave that you think of on a boat, but an internal wave inside the ocean that changes the location of the thermocline).
3. The wave propagates eastward and sets down the cool tongue of water in the Eastern Pacific Ocean.
4. As the cool tongue gets deeper, the trade winds become weaker, as there is now a smaller temperature difference between the Eastern and Western Pacific.
The difference in temperature between the Eastern and Western Pacific is one way scientists know if an El Niño is occurring or not. Smaller temperature difference = El Niño. The smaller temperature difference means the trade winds are weaker and the cold tongue is depressed = the first manifestations of El Niño. These first manifestations in the Pacific have HUGE ramifications for the rest of the world (those will have to wait for another blog post, or for you to check out the resources below), including, potentially torrential rains in California. Which would bring relief to drought stricken California (maybe). Science is all interconnected – what happens in the far Western Pacific Ocean does NOT stay in the Western Pacific Ocean.
A few disclaimers about the visuals:
1. I am not an artist. I am a scientist trying to use my right brain.
2. Figures are NOT to scale. The Pacific ocean is HUGE and the sea surface height difference is not that exaggerated.
3. The Julian-Madden Oscillation is not a large cloud that blows air into the Western Pacific – this is just for visualization (and I actually am still pretty fuzzy on what exactly is the Julian-Madden Oscillation).
If you want more science (or info on the potential economic impacts of another El Niño), check out the links below:
The (potential) economic and societal impacts of the current El Niño from NY Times Science
Will El Niño actually bring relief to California? Question explored by Here and Now
And if you want the most up-to-date El Niño forecast (and other really great explanations about El Niño and how it might impact the world) check out the National Weather Service Climate Prediction Center