On 23/05/10 09:11, Trevor Harley wrote:
On 2010-05-23 03:42:47 +0100, "jbm" said:
But it could be serious.
I've just downloaded the latest data from the weather station, and sat
here
looking at the graphs. First thing that came to mind was "Wtf did that
come
from?" At 6 o'clock yesterday morning, 0.6mm of rain was recorded, yet
when
I came to water the plants this evening, the water butt was all but
empty.
That water butt will fill easily with less than a millimetre of rain
(catches four roofs = 100+ sq m), so obviously no rain fell.
Since I keep a wildlife friendly garden, and assuming some pesky bird
(probably a pigeon) landed on the sensor and rattled it, how do you
prevent
that sort of thing happening. I certainly can't blame the dog for this
one.
Come on folks, one of you must some idea on this one.
My rain gauge was periodically disrupted by a robin sitting on the edge
and letting go.
I suppose you could erect a wire cage around it, but is it really worth
the effort? I suppose AWS across the country must be prone to and
therefor the rainfall consequently inflated by this sort of thing.
They say that prevention is better than cure, but in this case I agree
with Trevor. I expect your AWS has a way of correcting readings, so you
can archive a proper value for the rainfall. You can check the AWS
reading for rainfall by running a raingauge using a funnel/bottle
arrangement and working out the value from the diameter of the funnel.
A worse aberration of the AWS is one that happens every so often when
you get a sudden downpour that overwhelms the AWS. This happened
recently to me when we had a deluge of several mm in 20 minutes. The AWS
registered zero! When I went to look at it, I found the tipping bucket
was horizontal, and the first input from the storm had stopped it
tipping more than halfway. This of course is easy to correct using your
finger on the tipping bucket, if you know what the rainfall really was!
Have a look at my website (in my sigfile) to see the comparison I've
been running between the AWS and a standard gauge for over a year now.
Hugh
--
Hugh Newbury
www.evershot-weather.org