This equatorial region of the Western Pacific

This lesson will explore how the Walker Circulation works, as well as El Nino and La Nina. It will include how these weather patterns impact weather patterns around the world.

Walker Circulation

Hey there! My name is Sally Salmon, and I’m here to tell you all about some strange stuff that happens in the ocean and how it affects me and my salmon buddies. I’ll tell you all about El Niño, La Niña, and the Walker Circulation.

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Let me start with what happens when everything is ‘normal.’When there isn’t an El Ni;o or La Ni;a event and everything is ‘normal,’ you have a Walker Circulation, or the cyclic movement of air above the equatorial regions in the Pacific Ocean. And if you can grasp the Walker Circulation, you’ll have a better idea of how El Niño and La Niña work.Normally, the waters in the equatorial region of the Western Pacific Ocean are nice and warm. This warm surface ocean water warms the air above it, which causes an area of low pressure.

This is because the molecules in warm air are further apart, and they exert less pressure compared to colder, dense air.In addition to warming, the warm Pacific water adds moisture to the air. This warm, moist air rises, reaches its saturation point, meaning it can’t hold any more water vapor, and clouds and precipitation form.After the air releases its water, it becomes dry and heads eastward, where it eventually cools and sinks above the cooler waters of the Eastern Pacific. This cool, dense air forms areas of high pressure because, in cold air, the particles are closer together and exert more pressure. Wind blows from high pressure to low pressure, so this air in the Eastern Pacific blows back to the low-pressure areas in the Western Pacific.

These winds are known as the trade winds! Once the air gets back to the West Pacific, it re-warms, rises, and repeats. This cycling of air is the Walker Circulation.

El Ni;o

So, what does any of this have to do with Sally the Salmon? Right now I’m living in the North Pacific Ocean, and I migrate throughout my life, so I get to check out a lot of the North Pacific Ocean. Something that me and my salmon buddies really don’t like is called El Ni;o, which is a weather phenomenon where warmer than average temperatures are found near the equator in the Pacific Ocean. Even though I don’t live near the equator, El Niño impacts weather all around the world. The white on this image represents warm water, so you can see that El Niño really does change the temperature of water in the Pacific.

Let’s take a moment to explore how El Ni;o works. A really quick note first though. You may be wondering how it got the name El Ni;o, which means ‘boy’ in Spanish. I mean, is there a boy swimming around in the ocean magically warming it as he goes? A while back there were some fishermen near South America who noticed the water temperature was warmer than normal, and this coincided with Christmas, so they named it El Ni;o, which translates into ‘boy’ in Spanish.

They chose to name it El Ni;o after baby Jesus since it was observed near Christmas. So, remember there isn’t a little boy swimming in the ocean, but it’s still called El Ni;o.Okay, back to how it forms. Remember, normally the trade winds blow from the east to the west due to high and low pressure differences, and this is called the Walker Circulation. But, during an El Ni;o year, the trade winds subside or even change direction. This diminishing of the trade winds causes the warm water in the Pacific Ocean to stay put and stay warm along the South American coastline.

So, you’re probably thinking, ‘Big deal. How can a little warm water near South America impact the world and Sally Salmon?’ Well, let me start with how it impacts temperatures in North America. El Niño can cause cold winters in Canada, less snow and mild winters in the Midwest United States, and wetter conditions in the Southwest and Southeast United States. Worldwide, El Niño is blamed for tons of problems, like flooding in Peru and droughts in other parts of the world, including Australia and Indonesia.And when there’s an El Ni;o year, a lot of marine critters move into areas they don’t usually inhabit.

For example, some species move further north, like the rockfish, whereas other species can die. In fact scientists found that salmon around Washington and Oregon had high mortality rates and reduced growth rates following an El Niño event. And another study found that the ocean temperature in the Bering Sea rose ten degrees Celsius following an El Nño year and resulted in the deaths of millions of sockeye salmon. I know! Sad for salmon like me!

La Niña

Wow, talking about all that salmon death is bringing me down. Let’s move on! Next, there’s La Niña, which translates into ‘girl’ in Spanish and is otherwise known as the anti-El Niño. So, if it’s the anti-El Ni;o, I bet I don’t even need to give you a definition, but I will. La Niña is a weather phenomenon where colder than average temperatures are found near the equator in the Pacific Ocean.

And this is good for salmon, like me. Let me quickly describe how La Niña forms and its effects on the world’s climate. When there is a La Ni;a event, the trade winds near the equator are really strong, which causes warm water to blow westward. This leads to upwelling, which means that deep, cold water rushes to the surface to replace the warm water. This cold water can be found along the South American coastline.

The colder-than-normal ocean temperature causes changes all over the world. For example, in the United States, La Ni;a winters are characterized by dry and warm conditions in the South, wet conditions in the Pacific Northwest, and colder-than-normal conditions in the Northeast.Worldwide, La Ni;a is blamed for wet conditions around Northern Australia, sometimes causing dangerous floods in the region. In addition to Australia, La Ni;a causes increased precipitation in Northern Brazil and Southeast Africa. It also causes more intense monsoons in India and dry conditions along the west coast of South America.But, not only is La Ni;a better for me, it’s also better for fish living along the coast of South America. The upwelling of cold water also brings yummy food to the surface for all of those fish to eat! But, back to me.

My salmon friends and I really like cold water, so scientists find that there are greater salmon returns after a La Niña event.

Lesson Summary

I realize that was a lot of information. It’s worth noting weather changes like cold winters or increased precipitation in certain areas, but all of that information can become overwhelming, so let me review some take-home messages. The Walker Circulation is the cyclic movement of air around the equator, where warm air in the Western Pacific rises, becomes saturated, and releases its water as rain. Now that the air is dry, it heads eastward, where it cools, sinks, and then blows westward as trade winds. This cycle repeats itself.

The Walker Circulation occurs when there isn’t an El Niño or La Niña. El Niño is when warmer than normal temperatures are found in the equatorial regions of the Pacific Ocean. This is because the trade winds diminish or even change direction, which causes the Pacific Ocean surface waters to stay put. This is rough for a lot of marine critters, like me!La Niña is when colder than normal temperatures are found in the equatorial regions of the Pacific Ocean and is due to stronger than normal trade winds that blow warm surface waters of the Pacific Ocean away, which results in upwelling. This upwelling cools the surface temperature and is great for fish species because it brings nutrients to the surface.I realize I’m a long way from these equatorial regions, but El Ni;o and La Ni;a can be felt around the world, not just near the equator!


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