Ch-4,Part-2: Wind and Its Measurement; Wind Directions

[ Ch-4 Main ]   [ Exam-2 Topics ]   [ Geog-100 Main ]

• Wind is primarily the horizontal movement of air.
• This excludes updrafts and downdrafts.
• Undulating surface topography, trees and buildings cause turbulence in surface winds.  This means some vertical motion along with the horizontal.
• The turbulence effect diminishes to nothing at about a quarter of a mile above the surface.

What causes wind?

• Wind is the response to differences in atmospheric pressure from one place on Earth to another.

Anemometer (left); Wind Vane (right)

• Wind speed is measured with an anemometer (left in the figure).
  • Three conical cups catch wind.
  • The faster the wind, the faster the rotation of the cups.
  • An electrical signal is generated that is registered on a dial.
• Wind direction is measured with a wind vane (right in the figure).
  • The pointer aims at the direction from which the wind is coming, not where it is going!
  • A wind vane is often seen atop farm barns in the form of a metal rooster.
  • There is a "porcupine" wind vane in front of UI married student housing on Sweet Avenue.

[Study Fig 4-4, similar to that on the left.]

4-5: A wind compass

• Winds are named for the direction where the originate.
• Hence, winds are named for the direction from which they come and not for where they are going.
  • Thus a West Wind comes from the West and is going East.
  • Wind names are a half circle (180 degrees) different from where they are going.
• A wind compass displays commonly used names for winds (See figure, above).

[ Ch-4 Main ]   [ Exam-2 Topics ]   [ Geog-100 Main ]