Arctic Oscillation & North Atlantic Oscillation

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  • 0:01 Arctic Oscillation
  • 1:30 Arctic Oscillation…
  • 4:22 North Atlantic Oscillation
  • 4:55 North Atlantic…
  • 6:56 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

You've probably never thought much about the Arctic Oscillation or the North Atlantic Oscillation, but these weather phenomena impact global climates. This lesson explores each oscillation and describes the weather patterns associated with them.

Arctic Oscillation

When you say 'Arctic' a lot of things come to mind, like cold weather and maybe even the North Pole with flying reindeer, elves and Santa Claus. But Arctic Oscillation probably isn't one of the images that pop into your brain.

So what is this 'Arctic Oscillation?' Picture a teeter-totter. First, one side is up and the other is down, then one side is down and the other is up. The Arctic Oscillation is a lot like a teeter-totter, but instead of people bouncing up and down, you have changes in pressure and weather.

The Arctic Oscillation (AO) can be described as changes in pressure between the arctic and mid-latitudes. These pressure changes result in wind and weather changes. There are two different phases in the Arctic Oscillation: the positive phase and the negative phase. You can think of the positive phase on one end of the teeter-totter and the negative phase on the other end. These phases oscillate, or teeter back and forth all of the time.

A couple of things before we delve into these phases. Wind blows from high to low pressure, and the greater the difference between the pressures, the faster and stronger the wind. If you can remember, winds blow from high to low, you will have an easier time navigating the oscillations in this lesson. Finally, winds are named based on where they originate. So, if you have westerlies, you can assume the winds blew from the west. Okay, let's get started!

Arctic Oscillation Phases & Impact

The Arctic Oscillation is based on two pressure systems: one over the arctic and one over the mid-latitude region. Now, a little on the arctic pressure system before we go on. There is a continual pressure system in the arctic known as the polar vortex. In the positive phase, the polar vortex is strong, meaning there is a strong low-pressure system in the arctic. Meanwhile, the pressure system at the mid-latitudes is high. Remember: winds blows from high to low so this causes winds to blow from the mid-latitudes to the arctic. This causes fast moving westerly winds and northeasterly trade winds, which trap the cold air in the arctic.

Before we check out how the positive phase of the Arctic Oscillation impacts Santa and his crew, let's check out the negative phase.

During the negative phase, the polar vortex is weak, which means the pressure system is higher than normal in the arctic. And the high-pressure system in the mid-latitudes is lower than normal. Because the difference between the high and low-pressure systems isn't as great as it is in the positive phase, the winds are not as strong or fast. Also, because the high-pressure system is now in the arctic and the low-pressure system is in the mid-latitudes, the wind will flow from the arctic to the mid-latitudes. Because both of these factors, the winds lollygag along, which causes ridges and troughs. This allows the cold, arctic air to flow southward.

Now that you have a little background, let's see how these phases impact the weather. It's worth noting that this list of weather patterns doesn't address every weather pattern impacted by the Arctic Oscillation, but it does allow you to get the general patterns.

Let's start in Canada and Greenland and work our way across the globe. Check out the table to help you keep all of the weather patterns straight. During the positive phase, Canada and Greenland experience colder-than-normal temperatures because the cold, arctic air gets trapped. During the negative phase, however, the cold air travels further south, so Western Greenland and Eastern Canada experience mild temperatures.

Next, let's head over to Asia and Northern Europe. During the positive phase, these regions experience warmer temperatures and increased precipitation; however, during the negative phase they experience colder-than-average temperatures. Next, the Mediterranean experiences droughts in the positive phase and increased storms in the negative phase. Finally, let's head to the United States. In the Eastern United States, there are warmer temperatures during the positive phase and colder temperatures with storms on the Northeastern coast. And on the West coast, a positive phase causes warm and dry conditions and the negative causes cold conditions. And we can't forget about Santa. Because he is in the arctic, he will experience colder-than-normal conditions during the positive phase and warmer-than-normal conditions during the negative phase.

Location Positive Negative
Canada and Greenland Cold temperatures Mild in Western Greenland and Eastern Canada
Asia and Northern Europe Higher-than-normal temperatures and precipitation Colder-than-normal temperatures
Mediterranean Dry Increased storms
Eastern U.S. Warmer-than-normal temperatures Colder temperatures and increased storms on the Northeastern coast
Western U.S. Warm and dry Cold

North Atlantic Oscillation

Believe it or not, the Arctic Oscillation isn't the only weather pattern that acts like a teeter-totter. The North Atlantic Oscillation (NAO) is another weather pattern, but it is the fluctuation in pressure over the North Atlantic Ocean. It affects weather patterns around the world. Like the Arctic Oscillation, the North Atlantic Oscillation has a positive and a negative phase. The North Atlantic Oscillation has two pressure systems: one over the Azores, which is a high-pressure system, and one close to Iceland, which is a low-pressure system.

North Atlantic Oscillation Phases & Impact

During the positive phase the Icelandic low-pressusre system, also termed the Icelandic Low, gets really strong and the Azore high-pressure system, also termed the Azores High, gets really strong. This causes a huge difference between the high- and low-pressure systems, which causes the westerlies to get really strong. The strong westerlies prevent cold air from blowing south. Instead, the cold air heads towards North America. Sounds familiar doesn't it? Even though it's a different part of the world, the North Atlantic Oscillation works in much of the same way as the Arctic Oscillation.

A negative North Atlantic Oscillation occurs when the Icelandic Low is higher than normal and the Azores High is lower than normal. Both of these pressure systems are much weaker than they were during the positive phase. This causes less of a difference between high and low pressure so the winds are weak. The weak winds allow cold air to escape southward.

Let's see how the North Atlantic Oscillation impacts the weather. Again, this table doesn't address every single weather pattern associated with the Arctic Oscillation, but it will give you the general idea.

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