All About Air Pressure

How does air pressure affect weather? And why do storm systems spin in different directions? Everyday Einstein goes up into the clouds.

Lee Falin, PhD,
February 1, 2014
Episode #086

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Everyday Einstein podcast listener Robert wrote in this week to ask:

“With all the news about the cold weather that has gripped the U.S. lately, I've been looking at the weather map a lot and noticed on the surface maps that low pressure systems spin counterclockwise and high pressure systems spin clockwise. My question for you is why do low pressure and high pressure systems spin the way they do and does it have something to do with the Coriolis effect?”

Great question Robert! As I’ve mentioned before, weather and weather forecasting is extremely complicated, with lots of different factors involved. But let’s see if we can scratch the surface by looking at what air pressure is, how air pressure can affect the weather, why pressure systems spin, and just what the Coriolis effect has to do with anything. >

Under Pressure

If you look up in the sky, what do you see? Just air? What you’re actually seeing is about 50 miles of air. Despite being all light and, um, airy, the Earth’s atmosphere pushes down on you with a force of about 1 kilogram per square centimeter (or a little over 14 and half pounds per square inch). That’s a lot of air!

Like most other things, scientists have come up with lots of different ways to measure atmospheric air pressure (aka, barometric pressure) over the years. Just a few of these include include mmHg (millimeters of mercury), the torr, the pascal, the bar, pounds per square inch, and even something called the kip.

Whatever unit you choose to use, a device used to measure atmospheric air pressure is called a barometer. As air pressure increases, the measurement goes up, and people will say “the barometer is rising.” As air pressure goes down, we say “the barometer is falling.”


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