Monday, July 22, 2013

Spanish Fork Wind Rose

A wind rose illustrates wind direction, wind frequency, and wind speed. The direction of each bar shows where the wind blows from. The length indicates how often, in percent, the winds blow from that direction. The colors indicate wind speed.
This is a wind rose I created using a python script I found on the internet. Plotted is wind data collected from my weather station from March 13, 2013 to July 9, 2013.


Spanish Fork Wind Rose
Wind Direction, Frequency (%), Speed (mph)

Wind Direction, Frequency (%), Speed (mph)
March 13, 2013 to July 9, 2013 (c) bkb


You can see that 21% of the time winds blow from the South-South-East. This is the canyon wind. Wind blows out of the Spanish Fork Canyon at night. That is why Spanish Fork is such a great location for windmills. During the afternoon, winds blow up the canyon, but it appears winds from the northwest are less frequent.

I admit the location of the weather station is not ideal--a residential area and sandwiched between two homes. Wind channeled between the homes is why winds generally blow in two directions.

During this time period, sustained winds above 10 mph were rare. If we looked at wind gusts we would see higher wind speeds. The highest gusts measured by my station during the period is 28 mph.  
Spanish Fork Wind Turbines (c) bkb
Winds high above the surface are much faster. Wind turbines are built high because that is were the winds are the fastest. Friction near the surface slows down wind. However, for terrain induced flows, such as a canyon wind, the temperature gradients near the ground are what causes the winds. There is what is called an "exit jet." The fastest winds at the canyon entrance are probably 10-20 meters above the surface where there is less friction and where the driving force is still great. Placing those wind turbines in that jet will capture the most energy.

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