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The surface energy budget

The Planetary Boundary Layer

If winds in the middle of the troposphere can reach 60 mph, why isn't this the case at the earth's surface?

pbl The process of air blowing across the earth's surface creates friction. As you get farther above the earth's surface, the effects of this friction dwindle. Once you get high enough in the atmosphere, that friction is negligible.

The layer of the atmosphere that is subjected to frictional processes is the planetary boundary layer(PBL). The rest of the troposphere is called the free atmosphere because it is free of frictional influences.

What if there was no PBL? That would mean there would be no friction at the earth's surface. The winds would be fierce - often greater than 58 mph! Because of friction, the energy present in the upper atmosphere dissipates before reaching the surface, which keeps surface wind speeds relatively low.

Next page   -> what is the planetary boundary layer, continued

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