Anticyclones and Depressions
Knowledge - Why does air pressure vary?
If you are using a screen reader for this learning object start the screen reader support by selecting the Preferences link and then set the screen reader support to On. This screen explains why and how air pressure varies. It has an animation showing the circulation of air in a closed room with a hot radiator. Low pressure exists beneath the radiator as hot air is uplifted because of its low density.
Imagine a room in a house with a single radiator on one wall.
When the radiator is on the air around it is heated, expands, becomes lighter than the air nearby, and rises: the same principle as a hot air balloon!
The animation shows the convection cell that would result.
From this we can see that differences in pressure are due to differences in temperature, and where air is rising low pressure is produced at the surface and where air is falling it causes high pressure at the surface.
We can also see that the surface wind blows from high to low pressure.
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