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Radiation Shield accuracy

Discussion specific to Davis weather stations
Pete B
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Re: Radiation Shield accuracy

Postby Pete B » Sun May 23, 2010 10:17 pm

Mark's beaten me to it Ray, I was going to say something similar. :D

What is important is what is recorded in your location and asssuming one has taken all reasonable action to eliminate potential errors, then it's probably accurate for that location which is what you perceive when in the garden, not the airport conditions. You're luckier in some ways than me in having local official stations (the Airport & Woodford). As far as I know, there are no official stations in Malvern or Worcester, the nearest I'm aware of is Cheltenham (which held the UK record for 13 yrs from 1990 to 2003). There are however, loads of unofficial stations e.g. the conventional Stevenson Screen station just round the corner for me. It's going to be interesting to see their readings for this spell and how they compare with mine.

30.6C briefly here for me, well above any official reading. Looking at other maxima for the day in this part of the Country, some have been even higher. Obviously, I don't know anything about these stations, how they are set up and therefore, how accurate they are but it certainly felt a lot worse (I don't like hot weather like this) than yesterday generally. I was in the Countryside to the north of Worcester and it was unpleasantly hot. It's still 19.5C as I write now against 16.5C for the same time last night.

Before the widespread availability of good quality AWS's for amateurs as well as professional stations, most readings would have been obtained from manual stations, these being set up in 'optimum' conditions. Now, with AWS's, there are many more amateur stations set up in various conditions and of various accuaracy but whatever, will have added significantly to the number of daily reports available. Some of these will be more relevant than others but I wonder from how many of these stations with results being uploaded to sites like CWOP etc and therefore possibly getting into the various data sets have contributed to the perception of Global Temperature change? There is no doubt that there is a real change as evidenced by Arctic Ice and mountain glacier changes but it's possible that some change may be apparent from data being available from a much wider range of locations in various Countries than previously where no data had been available.

Pete B
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Re: Radiation Shield accuracy

Postby Pete B » Mon May 24, 2010 2:34 pm

Hi Ray, Mark (& others)

At this point, there is a "Cold Front" of some note between the Manchester area and Worcestershire, probably little, if any, 'weather' on it, just an air temp/humidity change.

Your stations are both registering around 20C, mine is up around 27C again with virtually all the stations around here reading above 25C, many above my 27C. Can't wait for the drop here, it'll be interesting to see the Davis sensors response rate when it comes through. ;)

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mcrossley
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Re: Radiation Shield accuracy

Postby mcrossley » Mon May 24, 2010 3:55 pm

Yep, it went through here yesterday afternoon. Noticably cooler, and a wind shift to the NW. Quite pleasent today :)

RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Mon May 24, 2010 4:26 pm

Pete B wrote:What is important is what is recorded in your location and asssuming one has taken all reasonable action to eliminate potential errors, then it's probably accurate for that location which is what you perceive when in the garden, not the airport conditions.

You're absolutely right Pete but I've been wrestling with the logic engrained in me that say's that if two stations either side of me are recording temperature X then logically so should I. But where my logic is failing is the environmental conditions where my ISS is located. When it was attached to the wooden post it was clear there were errors introduced because of its height and lack of air circulation. Now that it's 2-3ft higher those issues are hopefully history so yes, I should now be recording temperatures that are accurate for the environment. And although my reference station is recording temperatures very close to those at Man Airport they are not typical of temps in his garden but those on his roof.

You're luckier in some ways than me in having local official stations (the Airport & Woodford). As far as I know, there are no official stations in Malvern or Worcester, the nearest I'm aware of is Cheltenham (which held the UK record for 13 yrs from 1990 to 2003). There are however, loads of unofficial stations e.g. the conventional Stevenson Screen station just round the corner for me. It's going to be interesting to see their readings for this spell and how they compare with mine.

It could be lucky or it can turn into a stick that you beat yourself with! I suppose until you see how that Stevenson Screen is setup you won't know how accurate it is but if someone has gone to that trouble and expense it should be as accurate as a well setup AWS. Have you made contact yet?

30.6C briefly here for me, well above any official reading. Looking at other maxima for the day in this part of the Country, some have been even higher. Obviously, I don't know anything about these stations, how they are set up and therefore, how accurate they are but it certainly felt a lot worse (I don't like hot weather like this) than yesterday generally. I was in the Countryside to the north of Worcester and it was unpleasantly hot. It's still 19.5C as I write now against 16.5C for the same time last night.


Some are apallingly setup. One chap on UKWeatherWorld reported shade and sun temperatures! :roll: Here's an interesting thought. If you placed a Stevenson Screen in a small concrete back yard (think of Coronation Street) would it show meaningful temperatures? I know your ISS is setup in what I consideer ideal conditions so your 30.6C is down to its sheltered location. Just like Mark's in Wilmslow. My max today is 21.1C comapred to 20.2 at my ref. station. As long as it stays around 1C difference I'm happy.

Before the widespread availability of good quality AWS's for amateurs as well as professional stations, most readings would have been obtained from manual stations, these being set up in 'optimum' conditions. Now, with AWS's, there are many more amateur stations set up in various conditions and of various accuaracy but whatever, will have added significantly to the number of daily reports available. Some of these will be more relevant than others but I wonder from how many of these stations with results being uploaded to sites like CWOP etc and therefore possibly getting into the various data sets have contributed to the perception of Global Temperature change? There is no doubt that there is a real change as evidenced by Arctic Ice and mountain glacier changes but it's possible that some change may be apparent from data being available from a much wider range of locations in various Countries than previously where no data had been available.


You would hope that only certified stations' stats would make it into global climate models otherwise someone might misinterpret them and reach all the wrong conclusions! I'll keep my opinion of Al Gore to myself. ;)
Cheers,
Ray, Cheshire.

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RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Mon May 24, 2010 4:35 pm

Pete B wrote:Hi Ray, Mark (& others)

At this point, there is a "Cold Front" of some note between the Manchester area and Worcestershire, probably little, if any, 'weather' on it, just an air temp/humidity change.

Your stations are both registering around 20C, mine is up around 27C again with virtually all the stations around here reading above 25C, many above my 27C. Can't wait for the drop here, it'll be interesting to see the Davis sensors response rate when it comes through. ;)


Hi Pete and Mark,

Looking at my WU graphs I suspect it came through around 8am this morning. The temperature rise that started around 6.30am briefly flattened and then dropped before rising again. The wind veered from SSW to W bt interestingly, no change of pressure. It's been a very pleasant day with clear skies after lunch and lowish humidity. Hope it reaches you soon if you don't like the heat.
Cheers,
Ray, Cheshire.

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Gina
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Re: Radiation Shield accuracy

Postby Gina » Mon May 24, 2010 4:46 pm

It certainly seems that the location and surroundings of the various weather sensors play a very significant part - much more than the quality of the station components, in fact. The difference I have found from using a decent Stevenson screen in a clear area over grass and extending the wind sensor mast by several metres has quite surprised me. Unfortunately, I know many others haven't got the relatively good environment I have and sighting has to be a compromise. If you want to compare your readings with other stations, you need to know that their sighting and setup will give reasonably accurate readings.
Gina

Sorry, no banner - weather station out of action. Hoping to be up and running with a new home-made one soon.

RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Mon May 24, 2010 5:13 pm

Hi Gina,

You're very fortunate to have such conditions. I dream of open spaces in my small garden. I could, i suppose, locate that pole in the middle of my lawn but one has to be practical as the lawn has to be mowed. Given its height I think my ISS would not record significantly different temperatures from what I have now if I relocated it there.

I was keen to see how my reference station was setup and was quite surprised it was roof mounted. But that reassures me when I see my higher readings because roof temps will never be higher than garden ones although they can be identical on windy cloudy days.
Cheers,
Ray, Cheshire.

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RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Sat May 29, 2010 2:47 pm

I've been comparing my temps to that of my 'reference' station in Flixton - 10 or so miles away. Given the large range of temperatures we've had over the last fortnight it's been an ideal time for such a comparison. I've had to paste it as an image as I can't paste it direct from a Word table. The 'Alan' column refers to the Flixton station.
TempComparison.jpg


Even last Saturday and Sunday - the hottest days since last July - there's little difference which is very encouraging. A average difference of 0.6C confirms there's no need for the daytime FARS now. All in all a very satisfactory outcome. I hope this is of use to other enthusiasts who are also seeking nirvana in temperature accuracy. :D
You do not have the required permissions to view the files attached to this post.
Cheers,
Ray, Cheshire.

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gemini06720
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Re: Radiation Shield accuracy

Postby gemini06720 » Sun May 30, 2010 1:13 am

RayProudfoot wrote:I was keen to see how my reference station was setup and was quite surprised it was roof mounted. But that reassures me when I see my higher readings because roof temps will never be higher than garden ones although they can be identical on windy cloudy days.
Ray, are you very sure that the temperatures measured at or near the roof will never get as high as temperatures measured at ground (garden) level? :?

I beg to differ - on a cloudless sunny day, radiated roof temperatures can get much higher than ground/garden temperatures... ;)

RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Sun May 30, 2010 8:26 am

gemini06720 wrote:I beg to differ - on a cloudless sunny day, radiated roof temperatures can get much higher than ground/garden temperatures... ;)

Hi Ray,
You'll notice that one of my readings was cooler than my reference and it was a warm day so I suppose it will happen very occasionally. But we are close to Manchester - infamous for cloud and rain - so it will be very much the exception. Also, Alan is due to relocate his station into his garden soon so that comparison will change.

Does anyone know if temps above artificial grass will be substantially different to over natural grass?
Cheers,
Ray, Cheshire.

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Gina
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Re: Radiation Shield accuracy

Postby Gina » Sun May 30, 2010 9:08 am

RayProudfoot wrote:
gemini06720 wrote:I beg to differ - on a cloudless sunny day, radiated roof temperatures can get much higher than ground/garden temperatures... ;)

Hi Ray,
You'll notice that one of my readings was cooler than my reference and it was a warm day so I suppose it will happen very occasionally. But we are close to Manchester - infamous for cloud and rain - so it will be very much the exception. Also, Alan is due to relocate his station into his garden soon so that comparison will change.

Does anyone know if temps above artificial grass will be substantially different to over natural grass?
I know roofs certainly get hot and even in cloudy weather they warm up a bit.

With real grass water evaporates from the leaves cooling them down. This will not happen with artificial grass on a dry day. How much difference this makes I don't know.
Gina

Sorry, no banner - weather station out of action. Hoping to be up and running with a new home-made one soon.

RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Sun May 30, 2010 10:38 am

Gina wrote:I know roofs certainly get hot and even in cloudy weather they warm up a bit.

I'm guessing the increased height and subsequent increase in airflow would negate any higher temperature on all but the calmest of days.

With real grass water evaporates from the leaves cooling them down. This will not happen with artificial grass on a dry day. How much difference this makes I don't know.

Maybe if you buy posh plastic lawns the amount of heat they can absorb is reduced? :D
Cheers,
Ray, Cheshire.

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mcrossley
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Re: Radiation Shield accuracy

Postby mcrossley » Sun May 30, 2010 12:11 pm

RayProudfoot wrote:I'm guessing the increased height and subsequent increase in airflow would negate any higher temperature on all but the calmest of days.
Unless the prevailing wind blows the warmed air from the roof onto the sensor?

RayProudfoot
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Re: Radiation Shield accuracy

Postby RayProudfoot » Sun May 30, 2010 3:17 pm

mcrossley wrote:
RayProudfoot wrote:I'm guessing the increased height and subsequent increase in airflow would negate any higher temperature on all but the calmest of days.
Unless the prevailing wind blows the warmed air from the roof onto the sensor?

Mark,

Agreed but it's all a bit academic now as Alan will soon be moving it down from the stratosphere :)
Cheers,
Ray, Cheshire.

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Pete B
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Re: Radiation Shield accuracy

Postby Pete B » Wed Jun 23, 2010 1:47 pm

This is what I wrote back on 23rd May after a particularly hot day, what one may say was the first real test of my station/location on a truely hot day.

Pete B wrote:30.6C briefly here for me, well above any official reading. Looking at other maxima for the day in this part of the Country, some have been even higher. Obviously, I don't know anything about these stations, how they are set up and therefore, how accurate they are but it certainly felt a lot worse (I don't like hot weather like this) than yesterday generally. I was in the Countryside to the north of Worcester and it was unpleasantly hot. It's still 19.5C as I write now against 16.5C for the same time last night.

Well, now the Climatological Observers Link report for May is out and on the same day, the close nearby conventional station to me reported a maximum temperature of 28C exactly. Therefore, for the first time, there was significant drift between my recorded maximum and that of a nearby station. The previous months, Feb/Mar/Apr, showed well under 1C difference between my maximum and his maximum on the same day.Therefore, it looks as if a daytime (D) FARS unit could benefit my station on sunny/hot/still days. I have not reached that reading again since, the next highest max is just over 28C earlier this month but I'm expecting it to be exceeded over the next few days.

I don't really want to get into raising the ISS to 3m or anything like that as even if it does make a difference, it is no longer truely representative. Anyways, the extensive 'green' boundaries of the garden are now probably now getting to or even above 3m and will remain so till I cut them back down to ~2m high in the next couple of months. Therefore, over the next couple of weeks or so, I'll get hold of the D/FARS, get it fitted and further monitor my station vs the Conventional one around the corner.

Reading through the Weather Watch or Wx Forum posts, most posters on there who've already been there with the FARS question agree that the use of the FARS, even the D/FARS one does make the difference under the hot/still/sunny day weather conditions.

So, we'll see how it goes.

Pete


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