Atmospheric pressure and wind are related both qualitatively and quantitatively. Differences in pressure in the atmosphere are what create the phenomenon called wind in the first place. Additionally, earth scientists have developed a number of mathematical models to determine pressure as a function of wind speed, mostly using data gathered from storm systems.
No convenient predictive equation exists linking these two variables; instead, the relationship is an empirical one, with plots of pressure versus wind speed using a host of data points within the same system used to generate an equation using a mathematical method called linear regression. Using one of a number of related equations derived this way, if you have wind speed, you can calculate the pressure to within a reasonable margin of error.
Differences in air pressure between different points around the globe are fundamentally attributable to temperature differences, which in turn create differences in the density of air. As you might expect, winds tend to blow from areas of higher pressure to areas of lower pressure, in the same basic way that squeezing a plastic soda bottle drives air out of the mouth of the bottle.
Standard atmospheric pressure is 14.7 pounds per square inch (lb/in2), which equates to 760 millimeters of mercury (mm of Hg), 101.325 kilo-Pascals (kPa) and 1013.25 millibars (mb). The unit typically used in measurements within storm systems is the millibar.
Pressure, wind speed and temperature are interdependent, as noted. But researchers have developed two useful equations that eliminate temperature and relate wind speed to pressure directly.
Pressure as a Function of Wind Under Hurricane Conditions
The equation of interest in this case is:
P = 1014.9 – 0.361451w – 0.00259w2
With P in mb and w in m/s. For example, a wind speed of 50 m/s (about 112 miles per hour) would be associated with a local atmospheric pressure of:
1014.9 – 0.361451(50) – 0.00259(2500)
= 990.4 mb
Among the lowest pressures ever recorded is 870 mb, in the middle of a Pacific typhoon.
- The 0.0027 factor is based on certain assumptions, such as “normal” velocities, relatively flat surfaces, and normal air densities and temperatures. Extreme sizes, like the cross section of a pin or a building, may require different factors.
About the Author
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs.com and the editor of "Run Strong," he has written for Runner's World, Men's Fitness, Competitor, and a variety of other publications. More about Kevin and links to his professional work can be found at www.kemibe.com.