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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#11
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"Hugh Newbury" wrote:
Martin, It occurs to me that maybe the answer might be to restrict the outlet from the AWS to its tipping bucket. Small as it is, possibly it's still too large to cope with a deluge. The weight of the rain in the bowl would force the water out more quickly. Certainly my experiments today seem to suggest this. I'll think about it for a day or two. .... as John suggested (elsewhere in the thread) I would be reluctant to restrict the flow - it might (almost certainly will) lead to bigger problems. Indeed, I'd be reluctant to do anything to *physically* alter the collector/gauge until I was absolutely sure that the difference wasn't 'genuine' in the sense that there isn't another (external) factor accounting for the results. Looking at your data, you get some very close figures when the rain is 'steady', but the difference multiplies alarmingly when the rain is intense and accompanied by strong winds (which as others have stated seems to have been a feature of this summer), which would steer me towards an exposure problem, which the loss due to (attempted) rapid cycling of the sample accentuates. I know this is going to sound 'clunky', but you might want to consider mounting a passive collector adjacent to the AWS gauge (i.e. same height/not more than 30cm apart) - even a jam jar and a plastic funnel would do, just to see if it collects roughly the same amount of rain at that location. It's not ideal as one will interfere with the other of course, but I would hope that the difference wouldn't be more than 10%; at the moment, during some of your events you are getting differences of 30% or so. Martin. -- Martin Rowley West Moors, East Dorset (UK): 17m (56ft) amsl Lat: 50.82N Long: 01.88W NGR: SU 082 023 |
#12
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Is there not a better way of measuring rainfall? Rather than a
mechanical device like a tipping bucket that interferes with what is being measured, why not something comparitively non-intrusive? I'm thinking of some kind of device like a laser maybe. Surely a tipping bucket isn't the pinnacle of water measurement technology? -- comp.john at googlemail dot com |
#13
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comp.john wrote:
Is there not a better way of measuring rainfall? Rather than a mechanical device like a tipping bucket that interferes with what is being measured, why not something comparitively non-intrusive? I'm thinking of some kind of device like a laser maybe. Surely a tipping bucket isn't the pinnacle of water measurement technology? Splendid idea! Tell it to Davis (AWS makers in the US of A). They're still grappling with Micro$oft and have only just heard of USB connections! Hugh -- Hugh Newbury www.evershot-weather.org |
#14
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Martin Rowley wrote:
... as John suggested (elsewhere in the thread) I would be reluctant to restrict the flow - it might (almost certainly will) lead to bigger problems. Indeed, I'd be reluctant to do anything to *physically* alter the collector/gauge until I was absolutely sure that the difference wasn't 'genuine' in the sense that there isn't another (external) factor accounting for the results. I expect you're right: I actually wasn't going to do anything permanent, using putty/chewinggum etc. But I think I will tinker in a detinkerable way and see what happens. Looking at your data, you get some very close figures when the rain is 'steady', but the difference multiplies alarmingly when the rain is intense and accompanied by strong winds (which as others have stated seems to have been a feature of this summer), which would steer me towards an exposure problem, which the loss due to (attempted) rapid cycling of the sample accentuates. I know this is going to sound 'clunky', but you might want to consider mounting a passive collector adjacent to the AWS gauge (i.e. same height/not more than 30cm apart) - even a jam jar and a plastic funnel would do, just to see if it collects roughly the same amount of rain at that location. It's not ideal as one will interfere with the other of course, but I would hope that the difference wouldn't be more than 10%; at the moment, during some of your events you are getting differences of 30% or so. That's a good idea. I have a large funnel and lots of jamjars/bottles. I'll report back. Hugh -- Hugh Newbury www.evershot-weather.org |
#15
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Hugh Newbury wrote:
Splendid idea! Tell it to Davis (AWS makers in the US of A). They're still grappling with Micro$oft and have only just heard of USB connections! Hugh $deiety, really man this is so sad. If I could get a schematic of interface and protocol, I might just be able to transform an ancient cd-rom reader into a useful device! -- comp.john at googlemail dot com |
#16
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TBH I'm really not convinced that any amount of tinkering is going to
change things much. I'd be much more inclined to look at a way of getting your VP2 rain gauge down on to the ground. There are two ways of doing this with a VP2 gauge. One involves separating rain gauge and shield, which can be done with a couple of spare parts and a short extension lead. The other is simply to use a separate standalone 7852 Davis gauge (ie the old WMII one), which is still available and is plug compatible with the VP2 gauge. This option costs more but is significantly simpler to do. John Dann www.weatherstations.co.uk |
#17
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John Dann wrote:
TBH I'm really not convinced that any amount of tinkering is going to change things much. I'd be much more inclined to look at a way of getting your VP2 rain gauge down on to the ground. There are two ways of doing this with a VP2 gauge. One involves separating rain gauge and shield, which can be done with a couple of spare parts and a short extension lead. The other is simply to use a separate standalone 7852 Davis gauge (ie the old WMII one), which is still available and is plug compatible with the VP2 gauge. This option costs more but is significantly simpler to do. I'll try one of these later, perhaps. Hugh -- Hugh Newbury www.evershot-weather.org |
#18
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.... this might be of interest:-
http://www.onerain.com/includes/pdf/...ageRecords.pdf Martin. -- Martin Rowley West Moors, East Dorset (UK): 17m (56ft) amsl Lat: 50.82N Long: 01.88W NGR: SU 082 023 |
#19
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Martin Rowley wrote:
... this might be of interest:- http://www.onerain.com/includes/pdf/...ageRecords.pdf Martin, Indeed it is: fascinating! One has to wonder why the tipping bucket has been thought worth keeping for so long ( a century or more?). I have a dream ... An ordinary gauge like a std one and at std height, but with an electronic weighing device, as in bathroom scales, under the collecting part. The weight could be transmitted along with other data by wire or wirelessly as with the Davis etc. At 24hr intervals it could be emptied by hand or maybe automagically, and the device zeroed. Simple, efficient, reliable, except of course for the trees growing up, ground changes etc. I think I'll patent the idea. Meanwhile, back to the tipping bucket ... Hugh -- Hugh Newbury www.evershot-weather.org |
#20
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On Tue, 04 Aug 2009 08:34:55 +0100, Hugh Newbury
wrote: One has to wonder why the tipping bucket has been thought worth keeping for so long ( a century or more?). There have been quite a number of other designs too of course, eg syphon arrangements. I dare say someone could write a fairly extensive history (and may well have done so already for all I know). Most AWS systems will want a fully automatic - ie self-emptying - gauge and that presumably is the biggest challenge. The fact that the TBR (tipping bucket) design remains the commonest, at least among more affordable gauges, does rather suggest that it has stood the test of time as the most cost-effective and perhaps, for all its faults, least inaccurate/unreliable option. But I do think that you need to separate out the location of the gauge from its measurement mechanism. A VP2 gauge positioned on the ground would have the single biggest source of variability removed and I think you might then be surprised at the improvement vs a standard reference gauge. John Dann www.weatherstations.co.uk |
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