Tuesday, July 1, 2014

The Planetary Boundary Layer

Inversion over Salt Lake City: January 18, 2013
The Planetary Boundary Layer, or PBL, is the lower part of the atmosphere that interacts with the earth's surface. The two most important interactions that happen in the boundary layer are the transfer of heat and the transfer of water. On a clear summer day, radiation from the sun heats the ground. That heat is transferred to the atmosphere by conduction and convection which causes turbulence in the atmosphere. Water is also transferred to the atmosphere by evaporation. Rising thermals then carry the water vapor up to a level where it cools enough to form clouds and sometimes causes precipitation. In winter months the PBL acts differently and we get inversions that keep the valleys cold. In addition to seasonal variability, the boundary layer undergoes transitions on a daily cycle. Furthermore, the interaction in the PBL are different over oceans, ice, snow, swamps, lakes, mountains, forests, and deserts. Each of these surfaces have unique boundary layer processes that result in different types of weather. For that reason, in order to make accurate weather forecasts it's necessary we understand these different earth-atmosphere interactions. High resolution weather forecasts are largely dependent on accurate equations that simulate the interaction in the PBL.

Spanish Fork Land Use Categories.
Accurate classifications like this are useful
to implement a PBL scheme in a weather model.

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