RMS Speed explanation

[Craig Dabbs]

Hi there, 

Im all new to the weewx scene, im using a WMR100 station to mainly monitor wind speed.   As im not very clued up on weather terms i was wonderingg what does RMS mean?

Thanks

Craig

[Thomas Keffer]

RMS is "root mean square". That is, you square the velocities, take the average of that, then take the square root of the result.

Why is it useful? Because it reflects the "average energy." Remember, the energy of the wind goes as the square of the velocity. Strong winds count for more than weak winds. RMS reflects this.

Suppose you have no wind for an hour, then 20 mph winds for another hour. The average wind is 10 mph, but the RMS wind is 14.1 mph (=sqrt(20**2)), reflecting the extra energy of those 20 mph winds.

Hope that helps

-tk

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[Craig Dabbs]

That explains everything very well thanks Tom,  very handy to know for things like proposed wind turbines i imagine.

Cheers

[Brad Henderson]

Hi just wondering about this myself when I stumbled across this post. Thomas your explanation is correct I think, however, there is a small error in your formula below. 

I think it should read: 

RMS = sqrt(1/n * (x1**2 + x2**2))

In the case of your example:

RMS = sqrt(1/2 * (0**2 + 20**2))

         = sqrt(200)

         = 14.1

Cheers,

Brad

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