Southern Wisconsin has certainly experienced some windy days this past week.
Wind is defined as the horizontal movement of air from one place to another. Wind exists because of differences in air pressure.
Any movement requires a force, and in the case of wind, it is the horizontal pressure gradient that supplies the force. The gradient of an atmospheric variable measures the difference of that variable over a given distance. The pressure gradient is the difference in pressure over a certain distance.
Pushed by the pressure gradient forces, gases in our atmosphere move from areas of high pressure to low pressure. The larger the difference between the pressures over a given distance, the greater the pressure gradient force and the faster the air will move from the high to the low pressure.
The pressure, temperature and density of a gas are related to one another through a mathematical formula known as the ideal gas law. A change in one of these variables will cause a change in one or both of the others. Unequal heating of the atmosphere leads to pressure gradients which drive the winds.
A wind gust is a sudden, short burst of strong wind that moves faster than the current wind. As the wind blows, a number of things can interrupt air’s motion, such as trees, cars and buildings. Whenever air is obstructed in this way, friction comes into play and slows the wind. Once wind passes the object, it flows freely again, and its speed can increase abruptly. The speed of the wind, and the size and shape of the object that the wind is blowing against define how strong the gust will be.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.
