How Continents & Oceans Influence Global Pressure Distribution

Lesson Transcript
Instructor: Meredith Mikell

Meredith holds a B.S. in marine science with a minor in philosophy, as well as a master's of aeronautical science with a space science emphasis. She has taught subjects including marine science, biology, astronomy, math, and reading to students from kindergarten through high school.

The movement of air in Earth's atmosphere is driven by several variables, including differences in pressure. Here we will examine how the presence of land and ocean affect differences in pressure, followed by a brief quiz to test your knowledge.

Pressure in the Atmosphere

We have all seen a weather map before at some point, most likely on the morning news. The meteorologists talk of 'high' and 'low' pressure systems moving across the country, sometimes bringing severe weather with them. These areas indicate changes in atmospheric pressure, the force exerted on the ground by the weight of the air above it.

If you are standing at sea level, you are feeling the greatest amount of possible atmospheric pressure, since there is the most possible air sitting on top of you. Someone standing on the top of a very tall mountain would be experiencing lower air pressure - less air on top. But air pressure is not necessarily so simple; it routinely fluctuates throughout the atmosphere and across the surface. Pressure is affected both by factors that frequently change, temperature, for example, and factors that do not change, the presence of land and ocean.

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  • 0:01 Pressure in the Atmosphere
  • 1:08 Temperature and Pressure
  • 2:56 Air Pressure over Land and Sea
  • 4:49 Lesson Summary
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Temperature and Pressure

As you know, we live on a spherical planet. Earth's shape has a major effect on how it is heated which, in turn, has a major effect on how air moves across it. Because the equator absorbs more solar radiation than the poles, the atmosphere is warmer there. If you've ever worked with a convection oven, then you know that convection occurs when warm air rises and cool air sinks.

The same thing happens in Earth's atmosphere: that warm, equatorial air rises. Due to the Coriolis Effect, air is pulled with Earth's rotation and deflects away from the Equator, moving towards the poles and creating cells of updrafts and downdrafts, where warm air rises and cool air sinks.

When warm air rises, it creates a low pressure system where air has risen upwards, leaving less air pressure at the surface. Likewise, when cool air sinks, it creates a high pressure system where cool air has dropped down to the surface, bringing increased pressure. Because air tends to have water vapor in it, especially warm equatorial air, low pressure systems tend to include lots of precipitation and stormy weather when that warm vapor cools and condenses. High pressure systems, likewise, are usually associated with fair weather, as that cool air from way up in the atmosphere tends to be drier. So, next time you watch weather on the news, see if you recognize this connection between pressure systems and what kind of day can be expected.

Land and Sea

Now that you've seen how temperature can affect pressure in the atmosphere, we can also take into account the role of land in affecting the movement of air. If you've ever spent a nice, relaxing summer by a swimming pool under a hot sun, you've likely noticed how the concrete around the pool can become scorching hot and even burn the bottoms of your feet. And yet, even though it is being heated by the same sun, the water in the pool never gets quite that hot.

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