Author Topic: Beveled support causing wind lift on CoCoRaHS?  (Read 478 times)

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Offline miraculon

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Beveled support causing wind lift on CoCoRaHS?
« on: April 07, 2017, 08:34:40 AM »
After the episode about the shape of the Davis VP2 rain cone, and subsequent release of the Aerocone, I was musing on why my CoCoRaHS gauge seems to come out on the low side sometimes. It seems to be connected with southerly and easterly winds. With calm winds my NovaLynx 8" TBR agrees very well with the CoCoRaHS, as does the Davis.

I took a fresh look at my CoCoRaHS gauge installation, and I notice that my beveled board top end is very close to where the outer cylinder rim is. With the funnel installed, this will obviously be a bit better. I have been holding off on putting the funnel and inner cylinder in until the last snowflake has flown...

What I am beginning to wonder, is whether this bevel might be exacerbating wind lift also, just like the original non-Aerocone Davis. Even the "level and bevel" instructions on the CoCoRaHS site raises the possibility of this happening. I am fully aware of the reason for the bevel to prevent rain splashing into the gauge. I believe that this bevel might be causing an under-catch due to wind lift. I will try to raise the gauge up a bit, maybe add a baffle at the bottom of the bevel slope to hamper wind lift.

Greg H.




Blitzortung Stations 668, 706 - CWOP CW4114 -  CoCoRaHS MI-PI-1

Offline floodcaster

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Re: Beveled support causing wind lift on CoCoRaHS?
« Reply #1 on: April 07, 2017, 09:17:17 AM »
Hmm...interesting. :-k  Do you have a pic of your CoCoRaHS installation? For my winter reporting, I move my CoCoRaHS gauge to the same post I use for the ETo gauge in summer. It sits lower and therefore may be less prone to wind-induced undercatch of snow. I don't have any stats to back that up though. That may be a good study project for next winter.  ;)  I might try and locate another gauge at a lower height for summer for comparison. But you know how comparing two rain gauges, or two anemometers...goes. :-)

Bill
« Last Edit: April 07, 2017, 09:19:59 AM by floodcaster »
Bill


Offline miraculon

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Re: Beveled support causing wind lift on CoCoRaHS?
« Reply #2 on: April 07, 2017, 10:12:29 AM »
I just went out and took a couple of pics.

One is with the inner cylinder and funnel in place.

The other is without the funnel/tube and is the worst case.

I mounted the plate where it was due to the screw holding the board to the pole. I think that I will try counter-sinking it and see if I can move the whole works up.

I might try a baffle, if I can avoid creating a splash-in surface which would nullify the entire point of the bevel.

Greg H.
« Last Edit: April 07, 2017, 10:17:35 AM by miraculon »




Blitzortung Stations 668, 706 - CWOP CW4114 -  CoCoRaHS MI-PI-1

Offline floodcaster

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Re: Beveled support causing wind lift on CoCoRaHS?
« Reply #3 on: April 07, 2017, 11:38:05 AM »
Yes, I would think moving it up would help. Mine is on a post (not beveled) and even with the funnel out, it sits above the top of the post. Note: the post is actually level, the photographer wasn't.  ;)
Bill


Offline eyecue

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Re: Beveled support causing wind lift on CoCoRaHS?
« Reply #4 on: April 07, 2017, 12:34:31 PM »
https://www.cocorahs.org/media/docs/CoCoTrainingSlideshow_v9.2B.pdf

My take away is bevel is good.  As long as you don't have a solid fence line or obstruction. If your setup for the CoCoRaHS gauge is reading lower than a tipping bucket like the Davis system uses, you should always go with the reading from the CoCoRaHS because the NWS has never accepted tipping buckets as being accurate.
Cocorahs, Skywarn, Aficionado of weather. Davis VP2  pro wireless, Oregon Scientific and DIY.

Offline miraculon

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Re: Beveled support causing wind lift on CoCoRaHS?
« Reply #5 on: April 07, 2017, 03:41:22 PM »
OK, I was able to raise the mounting bracket by almost exactly 2 inches. (51mm)

I did need to countersink the upper attachment screw for the wood piece to the pipe (via conduit clamp).

It looks much better now and has significant clearance to the beveled wood especially with the funnel in place.

I'll monitor rain results for a while and see what, if anything this did.

Greg H.




Blitzortung Stations 668, 706 - CWOP CW4114 -  CoCoRaHS MI-PI-1

 

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