Notes

AIR MOVEMENT

And today, we're going to be talking about air movement. Our objectives for today are to explain why different latitudes on Earth receive different amounts of solar energy. We're going to describe what the Coriolis effect is. And then we're going to explain how land and water surfaces can affect the overlying air.
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So first of all, let's talk about how wind forms. As the Sun heats up the Earth, different latitudes or degrees high or low are going to receive a different amount of energy. Right in the middle, around the equator, is going to get the most direct sunlight. And because it gets the most direct sunlight, it's going to be heated the most. Near the poles, the sunlight actually has to bend in order to reach it. So that's where the energy is the least on the Earth. As the air gets heated, hot air wants to rise. The molecules begin to spread out and move a little bit faster and become less dense. And because it's less dense, it's lighter, so it rises up. Once it rises up, it's going to cool down. Cold air, on the other hand, wants to sink. So as that air gets cold, it's going to condense together and become heavier, so it will sink. And that's how wind eventually forms.
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There is something, however, called the Coriolis effect, that affects how the wind and air moves. The Coriolis effect is the effect of the rotation of the Earth, changing how the air is moving. If you can imagine being on a merry-go-round and throwing a ball to a friend on the other side, the ball will not go directly to your friend. Instead, because the merry-go-round is spinning, it will curve slightly. The same exact thing happens on the Earth. The Earth is rotating at about 1,000 miles per hour. And because it's spinning, the air that's moving through, that would normally be going in a straight line, curves a little. And so that's how we can get surface winds that will curve. Around the Earth, there's going to be lots of different kinds of winds. The surface winds on the Earth are affected by the movement of the seas, by the heating of the Sun, and the Coriolis effect. There's also winds in the upper troposphere, which is the layer of the atmosphere that we are in, until about 10 kilometers high. In the upper troposphere, there is what we call jet streams, which are very strong winds that are constantly blowing in the same directions. Plane travel has actually learned about the jet streams and they can use that to their advantage. If they get into the right kind of jet stream, they can improve how fast they get someplace. If they're going against the jet stream, they're going to fly a little bit lower so they won't be pushing against it. There's also local wind systems whenever you have a large body of water next to land. What happens is land heats up and cools down much more quickly than water does. So during the day, the land gets hot. The hot air rises and blows over to the sea, The sea cools it down and it sinks and it goes back over towards the land. So you're going to get a circulation going up over the land, out towards the water, and back to the land. Where at night, it reverses. The land cools down. So the cold air sinks over the land, goes out to sea. The water warms it up. Because comparatively it's warmer than the land was, it rises up and moves out. So again, during the day, it's going to circulate one way. During the night, it's going to circulate the other way. And this will affect greatly the climate of any kind of land around a large body of water, because you're constantly going to have sea breezes.
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Just to review our objectives, we explained why different latitudes on Earth receive different amounts of solar energy. Remember, at the equator the sunlight is going to be hitting it directly, so it's going to get the most solar energy. Whereas at the poles, the sunlight is not coming in directly, so it's not to receive nearly as much of the energy. We described what the Coriolis effect is. Remember, that's the effect of the Earth rotating and bending whatever is moving through, like air and water. And then we explained how land and water surfaces can affect the overlying air. Remember any time there's a large body of water, you can get a circulation going one way during the day and the other way at night.
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Coriolis effect: The apparent curving of the path of a moving object from an otherwise straight path due to the Earth's rotation.
jet stream: Narrow belt of strong winds that blows near the top of the troposphere.
land breeze: Movement of air from land to sea at night, created when cooler, denser air from the land forces up warmer air over the sea.
sea breeze: Movement of air from sea to land during the day when cooler air from above the water moves over the land, forcing the heated, less dense air above the land to rise.
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The curve of Earth’s surface means that solar waves hit Earth at different angles. Panama is located near the equator and receives more direct rays and more heat than Antarctica which is located near the south pole. Sea and land breezes are caused by convection currents. The rotation of Earth causes moving fluids to appear to move east to west in the southern hemisphere and west of east in the northern hemisphere in a phenomenon known as the Coriolis effect. Sailors travel at different latitudes when moving east and west because the direction of the prevailing winds varies with latitude. Sea breezes occur during the day because solar radiation warms the land more than the water. This causes the warmer air over the land to rise. The resulting convection current causes wind to blow in from the sea. Land heats and cools faster than water. The Trade Winds would appear to be moving west, or to the left; the Coriolis effect. Jet streams are narrow bands of strong winds that occur in the upper troposphere.