Slow wind speeds: obtain information form wind vane?

[swr03crw]

Background
I notcied last night was clear and calm: thus the wind dropped to zero and the tempeatures cooled.
Accordingly cumulus recorded the direction as zero (the convention used when wind speeds are zero).
My thoughts
However, wind speeds were NOT entirely zero: clearly by the fact that the wind vane turned occasionally (showed in the instantaneous values on the attached graph, but alas not in the datalog since the average was zero).
When the wind vane stalled then the wind really DID go to zero (as backed-up by the faster cooling temperatures at those vane-stalling times).
MY POINT: We have evidence of non-zero winds as long as the vane changes from one period to the next. However, these non-zero wind speeds are logged as zero. Can we perhaps have the gust values in these times set to the lowest equipment value (or, say, half of the lowest value?)
The logic:
IF WindDirectionChange~=0 AND WindSpeedGust==0
THEN WindSpeedGust==0.5
ENDIF
(notation: ~= means is not equal to)

Would be nice to see this mod implemented...
Curtis

PS. I have a LaCrosse WS2350

[steve]

This just seems... wrong... to me. It seems to be ascribing an accuracy to the equipment that it doesn't have. If it's not capable of measuring a wind speed below a certain level by normal means, then any attempt to come up with a figure below the minimum that it's capable of is just guesswork. But, that aside, what is the 'lowest equipment value' for your station (or any other station?). In theory, for the WS2300, it's 0.1 m/s, but it would perhaps be interesting to know what the lowest non-zero value is that you have recorded.

Does anyone else have any thoughts on this?

[beteljuice]

... MY POINT: We have evidence of non-zero winds as long as the vane changes from one period to the next...

Would you count a very short 'puff' as a windspeed to be measured ?

A pigeon sitting on your vane will also alter its apparent direction. Until there is a 'steady' wind, direction is meaningless. I substitute 0o with --- or null.

[swr03crw]

It is NOT wind direction I'm interested in (that should remain zero). I agree that wind direction at such low wind speeds is meaningless (or at best not measurable from ameteur equipment).
What I AM interested in is the fact that there clearly are tiny gusts of wind (i.e. these short-lived 'puffs'). Indeed one can often see them with your eyes on the cup - but it doesn't register a wind speed.
I was excited at how nicely the temperature and wind matched overnight (when the wind vane moved about the temperature didn't drop much [because of mixing]; but once the wind vane was stationary the air was static and thus allowed a stronger cooling of the air).
I think it is a clear case that there were small gusts of wind on some occasions (i.e. not quite zero wind gusts), whilst still conditions on others (i.e. REALLY a zero wind). The graph shows that.
What I am interested in is logging this somehow (what we call this is another matter: we could call it 'not quite calm'!, or give it a very low number, e.g. 0.1).

NB. in answer to your question the lowest value in my 5min cumulus values over the past week was 0.7mph (c. 0.3 m/s ?)

[steve]

I can see what you're trying to achieve - it's the equivalent of an observer recording 'trace' for rainfall with a manual rain gauge. It perhaps needs a bit of care over exactly how it is implemented; maybe a special value (negative?) that means 'not calm' and is interpreted appropriately by Cumulus.

[swr03crw]

Thanks for seeing my point.
I think the 'trace' analogy is perfect.
It would be nice to see it implemented in the future, but (as you say) care would be needed on how it would be recorded in the log and on any graphs, etc.

[swr03crw]

OK, here's an wacky idea for implementation:
For real calms (where there is NO vane or cup movement AT ALL), mark the value as -0 (i.e. negaive zero)
For near-calms (my effect of the moving vane during near-zero wind speeds), then mark as +0 (i.e. positive zero)

* Most data-analysis tools would merely interpret both values as 0 (zero), including Excel.
* Any user who wanted the special data, could then process their text files manually (e.g. by replacing the +0 values accordingly).

I'm not a mathematician, but I'll bet there are researchers who've spent much time thinking about negative zero

[steve]

It's a nice idea, but it doesn't look like SQLite allows you to differentiate between +0 and -0.

[swr03crw]

As you'll see I'm quite new to cumulus, so i don't really know your philosophy! I wonder if fundamentally you'd be keen to try to include this mod somehow. My reasoning for thinking about this one is that it is not possible to post-process these +0 wind speeds from the log (since wind direction is recorded as zero in the log).
If you/people were happy, I'd be keen for this effect to be included somehow.
So far, I guess the only options of inclusion would be to have the gust as +0.001 or -0.001. I guess I like +0.001 because a minus value might confuse someone who didn't notice the convention.

Anyway, I'll hope others have opinions on this (i.e. must get back to work...).
Cheers.

[steve]

I think we may have been talking at cross-purposes; I'd assumed you were suggesting this for Cumulus 2. I'm only doing bug fixes in Cumulus 1 now. That's not to say that I'll never do any more enhancements, but for now my focus is Cumulus 2. I should probably make this clear somewhere prominent, if I haven't already.

Cumulus 2 uses an SQLite database, so a scheme would need to be devised that worked with that. It could be a negative value, which Cumulus interpreted appropriately so that the negative value was never actually seen anywhere. Or something like that...