Effect of friction on winds, cont

  • Friction slows down the winds

  • as a result, which force becomes smaller, the PGF or the CF?? ANSWER

  • therefore, the winds cross the isobars, directed towards the lower pressure

  • the friction force is in the opposite direction as the wind direction

  • hence, the forces acting on the wind in this situation are:

  • friction + CF + PGF = 0

  • again, the effect of friction on wind is dominant near the surface, in the part of the atmosphere we call the boundary layer

  • the boundary layer extends from the surface to about 1-1.5 km AGL


1.  If the earth were not rotating, how would the wind blow with respect to centers of high and low pressure?

2. Why are surface winds that blow over the ocean closer to being geostrophic than those that blow over the land?

3.  If you live in the Northern Hemisphere and a region of surface low pressure is directly west of you, what would probably be the surface wind direction at your home? If an upper-level low is also directly west of your location, describe the probable wind direction aloft and the direction in which middle-type clouds would move. How would the wind direction and speed change from the surface to where the middle clouds are located?

4.  Consider wind blowing over a land surface that crosses a coastline and then blows over a lake. How will the wind speed and direction change as it moves from the land surface to the lake surface?


  Now test your knowledge of how the coriolis, pressure gradient and frictional forces affect wind speed and direction with this interactive tool.