"George Booth" wrote in message
...
On 25/02/2016 10:23, John Hall wrote:
In message , Eskimo Will
writes
snip
The MetO fully intend to make use of WOW information in model analyses
and a whole host of other data types. They will be able to do this due
to improved data error co-variances and some cunning mathematical
trickery which I cannot go into here. This is due to happen by the end
of this decade.
That makes me a little uneasy. Will they be able to get rid of all the
wrong data, of which I'm sure there must be a lot on WOW? And there's
also the opposite problem that, the more stringent their checks, the
greater the risk that some valid and important - but unexpected - data
might be discarded. Take the Hampstead thunderstorm in August 1975, for
instance, when a phenomenal amount of rain fell in an hour or so when
IIRC practically everywhere else in the country was dry. I can imagine
the vetting algorithm seeing a WOW report of say 160mm of rain and -
with no other reports of rain - deciding that it must be a typo for 16mm
or even 1.6mm.
Yes, these were my thoughts as well. If you look at the WOW homepage there
are very obviously a (minority) of AWS which suffer from poor exposure
and/or inaccurate instrumentation. The same thing is obvious when looking
at Weather Underground maps as well. As long as some filtering/moderation
of data from such AWS data takes place then I would agree they have a
value. I would add that all the folk I've spoken with over the years
who've set up AWS have been most conscientious in ensuring that their data
is as accurate as can be. However we now have a lot of low cost units
available which are set up with insufficient regard for siting
requirements.
That's where the clever mathematical stuff comes in taking account of the
error covariances. Basically you extract what you can from the WOW data but
giving it low weight compared to SYNOPS etc but it will still add value. I
did a study many years ago where it was concluded that for fog observing
what was needed was not just well-sited obs but loads of obs, even if they
were poorly sited or just plain wrong. Also don't forget the model itself
will have some idea what to expect from an observation, especially if the
assimilation is continuous, so it will be able to better decide how much
weight to give it. In the Hampstead storm situation it would "know" the
situation was convective and so a sudden report of 160mm would not surprise
it - clever stuff isn't it?!
Will
--
" Some sects believe that the world was created 5000 years ago. Another sect
believes that it was created in 1910 "
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
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