Factory Stevenson Screen mods

[Stephenwx82]

Hi everyone,

Well I modified my Stevenson screen for my WH3081 and 1081 stations and it has met with success with measurements taken off 2 x manual mercury thermometers that I own.

Its really simple to modify these screens into deliver fairly accurate temps in full sun so I thought I would share what I have done so I can share my success with other fine offset users.

First I painted the Stevenson screen in vivid white gloss (6 coats worth), I replaced the screen over my sensor with the 1081 screen whilst doing this which has had the same treatment, it requires you wrap the solar sensor and plug in newspaper or another covering to prevent it from being ruined by paint on the surface. Use a bit of coathanger wire put through the solar sensor hole which you need to unbolt and hang the screen or simply hold it up and apply several mist coats. The light reduction and radiation reduction is phenomenal.

I also took the opportunity to install a heat exhaust flue to augment the airflow upwards out of the station as I've always been quite worried that it can't dump heat directly upwards utilising effective convection unlike a double louvred double roof proper Stevenson screen. The tubing used was just white about 7.5mm across with a hole drilled into the side that sits away from the sun, the tube fits snugly in and is about 5mm into the screen itself, it terminates just under the flange for the solar sensor.

I also have a base that I trialled with the 1081 and carried over to stop radiation from getting in underneath its just a white lid with the hole cut to accomodate the square fitting underneath the temp/humidity sensor, really easy to do and another great way to keep that radiation out!

Anyways here are a couple of pics to give you an idea of what I have done:



and

Stephen

[serowe]

I notice you have put a flue into the screen to assist in ventilation, but airlfow through it is part of the Stevenson Screen design - it is partly this that leads to uniformity around the world no matter where the screens are placed.

I realise you have compared the temperatures to mercury thermometers but what you are really comparing is that everything inside the screen is measuring the same thing. If you really want to check it's effectiveness have you tried comparing the readings to Albion Park Rail - that would be the closest AWS to you (about 2km from Oak Flats but obviously depends on exactly where you are located). http://www.bom.gov.au/products/IDN60801 ... 5748.shtml will give you readings every 30 minutes you can compare to plus you can download the past 12 months worth of readings for overall comparisons.

(Having worked with the BOM for many years it was, well, surprising to see the 'contraptions' some people built to 'air condition' their thermometers/rain gauges etc - yet many of these people - many of the farmers - never thought about calibrating or checking their instruments to see how close to accurate they really were).

[Stephenwx82]

Yes overall I have compared readings to Albion Park AWS, a Davis station close by and Bellambi AWS. In a double louvred wooden screen that houses my mercury thermometers the air is able to be vented via the inner roof, due to the nature of the factory screen there is every chance that heat becomes trapped in the curved roof. The termination point is also so high so that the solar module protects it more from wind and rain, I was very conscious of this when plotting it out.

The flue in the screen is that small I doubt it will induce windchill it merely just brings air movement up to scratch like in a standard stevenson screen hence the proper accuracy. In essence a Stevenson Screen has 2 rooves for a reason and that is to allow maximum airflow, minimise radiation and give an accurate measure whilst keeping it from windchill. Heat pooling in a single roof design that is curved like these is a strong possibility.

I don't compare to the Albion Park AWS exclusively because the fluctuations are quite large in this part of the world due to different terrain, proximity to water bodies and ocean even the seabreeze boundaries cause major local differences. Thats why I have a manual stevenson screen housing manual thermometers.

I'm friends with a few BoM workers, very active stormchaser and part of the Australian severe weather association, been on the chase for over 10 years now

Unlike farmers and such I have the real deal Stevenson screen sitting in my yard with manual thermometers to check calibration and with this design I have tested it and it has come up trumps

Can't wait to start my long overdue B. Sc - Maths and Physics this year it will sure beat all of my past jobs thats for sure.

[serowe]

I have the real deal Stevenson screen sitting in my yard with manual thermometers to check calibration and with this design I have tested it and it has come up trumps

Don't happen to have the drawings for it do you? I used to have some before I left the Bureau (worked in satellites and comms in their HO in Melb) and now can't, for the life of me, find the damn things! (I'll probably find them the day I decide to throw everything out of the study - or the kids will find it when they throw everythng out after they have buried me!)

[Stephenwx82]

LOL its always the way isn't it!

I'll check my other hard drive but no promises I made it a few years ago from drawings a dear old friend of mine constructed his screen from. Could have been formatted from the planet by now

I'm just a tinkering sort of person I could have just housed the sensor in the proper screen first but being seperated earlier this year I like challenges to keep me busy between storm days.

[serowe]

LOL its always the way isn't it!

I'll check my other hard drive but no promises I made it a few years ago from drawings a dear old friend of mine constructed his screen from. Could have been formatted from the planet by now

I'm just a tinkering sort of person I could have just housed the sensor in the proper screen first but being seperated earlier this year I like challenges to keep me busy between storm days.

LOL think that's what happened to my drawings as well - the hard disk it is on is probably one of the coasters I now use around the house (old HDD's are great for that except the modern drives using screw heads that almost imposible to open!)

[Stephenwx82]

LOL its always the way isn't it!

I'll check my other hard drive but no promises I made it a few years ago from drawings a dear old friend of mine constructed his screen from. Could have been formatted from the planet by now

I'm just a tinkering sort of person I could have just housed the sensor in the proper screen first but being seperated earlier this year I like challenges to keep me busy between storm days.

LOL think that's what happened to my drawings as well - the hard disk it is on is probably one of the coasters I now use around the house (old HDD's are great for that except the modern drives using screw heads that almost imposible to open!)

thats what sledgehammers are for , no luck finding them yet, will search more as the night progresses.

[Stephenwx82]

no luck on finding them on my hard drives but I'll check emails when I get the time, on stormwatch at this point in time with cells about 50km to my south and a good chase day coming tomorrow

[serowe]

no lucky on finding them on my hard drives but I'll check emails when I get the time, on stormwatch at this point in time with cells about 50km to my south and a good chase day coming tomorrow

Have a Kit Kat errr sorry a break - they've just cancelled the severe thunderstorm warning (at 1035pm) although radar is showing some pretty colours between Nowra and Point Perpendicular...

[Stephenwx82]

yeah thats what I'm looking at, don't need severity just CGs for photography

[Stephenwx82]

current rate about once every minute can see them near Berry