Wind shear is the change of wind speed and/or wind direction over a certain height.
Why do I care? Agricultural pilots deal with wind shear on a regular basis when flying planes such as crop dusters. When spraying crops, these planes tend to fly low so that the sprayed material goes in the direction and location the pilots want. Wind shear in the atmosphere is also associated with severe weather and tornadoes.
Figure A: Change of Wind Direction With Height (Image fromNOAA)
In general, wind speed increases with height as you go up in the atmosphere. This is because friction from the ground slows down the air at the surface. The wind often changes in direction as height increases as well.
Let’s say one day you decide to climb a radio tower and you want to take wind observations as you climb up in the atmosphere. At the surface, you may notice that the wind is out of the southeast at about 5 mph. After climbing a couple of hundred feet to the middle of the tower, you notice that the wind is now out of the south at 15 mph. Once you reach the top of the tower, you notice that the wind is out of the southwest at 20 mph. What you just observed while climbing the tower was wind shear, i.e., wind changing speed and direction with height.
Want to learn more?
General Circulation of the Atmosphere
Activities to accompany the information above:
Activity: Wind Dynamics and Forests (Link to original activity.)
Description: This activity will assist students in understanding how forest density impacts wind speed through the forest. Students will make a model out of 2-liter bottles which will represent the forest and observe how the wind speed changes depending on the amount of trees within the forest.
Relationships to topics: Wind Shear