Daily Wind Patterns: Understanding of Processes
Roel Vining and Dr. James Gregory
Wind speed is an important variable when studying the likelihood and intensity of
air quality degradation. High wind speed coupled with other environmental conditions can
result in serious wind erosion events like that which occurred in California on Interstate
5 in November 1991, resulting in a 64 vehicle accident. Alternately low winds reduce
transport of particulates and gases, and increase the potential of odors from feedlots.
Historically, a model based on a sine wave has been used to model mean diurnal variations
in wind speed. This paper reports on the function and nature of variations in diurnal
changes in wind speed.
This study builds on previous work done by the authors to describe diurnal wind speed
and relative humidity patterns at six locations in the Great Plains. That study found that
mean diurnal wind speed is almost constant during dark hours, and follows a parabolic
curve during daylight hours. Hourly wind speed data were gathered for 10 locations in
different climatic regions across the country: Spokane, WA, Phoenix, AZ, Fresno, CA, Salt
Lake City, UT, Casper, WY, Bismarck, ND, Des Moines, IA, Baton Rouge, LA, Albany, NY, and
Atlanta, GA. Monthly averages of temperature for each hour of the day were calculated and
compared to models previously developed from the Great Plains locations and to a sine wave
model. While there were considerable differences between the average wind speed at each
location, diurnal variations displayed patterns similar to those previously identified.
While providing an acceptable statistical fit, a sine wave model does not adequately
describe breakpoints and the shape of diurnal wind speed patterns. The residual error is
certainly not random.