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Wind mean speed and gusts anomaly

From build 3044 the development baton passed to Mark Crossley. Mark has been responsible for all the Builds since. He has made the code available on GitHub. It is Mark's hope that others will join in this development, but at the very least he welcomes your ideas for future developments (see Cumulus MX Development suggestions).

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freddie
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Wind mean speed and gusts anomaly

Post by freddie »

I've been seeing this behaviour for a long time (a couple of years or more), so thought I should make a post as it looks incorrect to me. The two graphs below show wind speed (10 minute mean) and gusts (10 minute maximum). Logging and plotting interval is one minute.
wind-20211126.png
wind-20211128.png
I don't understand how the 10-minute maximum gust could be less than the mean speed for the same 10-minute period. I notice this behaviour only when wind speeds are decreasing. It is almost as if the mean speeds are "offset" to the right.

If you take a very simple example with a 10 min logging/plotting interval, with a speed of 10 at the start of the period and 5 at the end - and no gustiness/variation. You should have a mean speed of 7.5 for the whole period (plotted at the end of the period), and will have a 10-minute gust speed of 10 (plotted at the end of the 10-minute period).

Or am I missing something?
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Freddie
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mcrossley
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Re: Wind mean speed and gusts anomaly

Post by mcrossley »

I suspect a miss set option somewhere. As you say it is just plain wrong. I never see anything like that - https://weather.wilmslowastro.com/graph ... t.php#wind

For the Davis stations "Average Wind Speed" and "Speed for average calc" should both be un-checked

I'll have a dig into the code later.
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HansR
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Re: Wind mean speed and gusts anomaly

Post by HansR »

I assume it has to do with a mix of CumulusMX calculated values and station received values.
I let all values calculate by CMX so that no misunderstanding can take place.
Hans

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CMX build 4017+ ● RPi 3B+ ● Raspbian Linux 6.1.21-v7+ armv7l ● dotnet 8.0.3
freddie
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Re: Wind mean speed and gusts anomaly

Post by freddie »

mcrossley wrote: Mon 29 Nov 2021 9:48 pm I suspect a miss set option somewhere. As you say it is just plain wrong. I never see anything like that - https://weather.wilmslowastro.com/graph ... t.php#wind

For the Davis stations "Average Wind Speed" and "Speed for average calc" should both be un-checked

I'll have a dig into the code later.
I had both those options checked. I un-checked them on 30/11/2021 at 07:00. The difference I notice within a couple of hours is a more "blocky" graph for speed - which, I assume, is down to the Davis station rounding its mean speed to the nearest mph. This is a bit annoying, but doesn't bother me massively as long as it is accurate.

I will monitor - especially at times where speeds are decreasing.
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mcrossley
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Re: Wind mean speed and gusts anomaly

Post by mcrossley »

The Average Wind Speed is less important - once you have confirmed that the speeds look reasonable now, you could re-enable that if you want the decimal average (I get that from the WLL anyway which does do sensible averaging)
freddie
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Re: Wind mean speed and gusts anomaly

Post by freddie »

mcrossley wrote: Wed 01 Dec 2021 2:03 pm The Average Wind Speed is less important - once you have confirmed that the speeds look reasonable now, you could re-enable that if you want the decimal average (I get from the WLL anyway which does do sensible averaging)
I re-enabled Average Wind Speed yesterday morning, after running several days and convincing myself that mean speeds were now behaving correctly. The curve has smoothed out nicely so I am happy now.

The mean speed seems much more responsive now, matching with what I observe out the window. I would love to go back and re-run the past 16 months wind speed data with my current settings but that would be impossible. I can think of several windy days last December and February which would benefit from this.

Thanks to all who made suggestions.
Freddie
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