temperatures

Those are fahrenheit? Hell, you get differences like that just with sun shadowing. In areas where there are no large water bodies to temper things, a 20 degree Celsius change can be expected during the course of a day, with no great alteration in the 'weather'.

Long term data requires long term commitment in recording so universities, research institutes and maritime/shipping services will have the longest records of temperature, barometric pressure and wind direction/velocity.

Unknown local weather station reports for a single point in 'internet manual updating' time are the last source of info you'd use to determine long term trends, or even hourly trends.

Isn't there a federal service that gives you better weather forecasting for your area?

example:

RL

No, I have a thinfilm platinum RTD in free space, under a wooden stairway on the north side. Lots of trees around. The geometry has very little radiation cooling.

Sounds like those Stevenson boxes are generally sited in sunlight. I've seen them up on poles. White paint is generally black at thermal IR wavelengths.

My concern with official temperature measurements is the wild variation within a fairly small local region. Measuring a few tenths of a degree longterm trend, or declaring record highs, is silly when the sensors often disagree by, say, 20C.

temps

the

It is also considerably sheltered from the wind by that position. You aren't necessarily measuring the true air temperature there.

Which means that the Stevenson box tends to slightly underestimate the temperature at night when there is no inbound solar flux. The sun is principally an emitter of visible light and the white helps reflect that away. Stephenson screens work a lot better than you think.

or

Some of it is real. Microclimates of valleys can be radically different depending on the wind direction and time of day.

John Larkin schrieb:

the

Hello,

but what about the influence of the wall near the RTD?

But you don't know if they use a white paint which is white at IR too.

or

In Erlangen, many decades ago they brewed beer using ice from small lakes for cooling. The ice was cut into blocks with saws and stored in deep underground cellars and was stored there for several months. This was before they used ice from industrial production. Nearly every winter was cold enough to harvest enough ice. In the last decades we had very few winters here with thick ice on the lakes.

Bye

the

It's cinder block. The other side is an unheated garage, so at most the weak coupling to the wall will add a little time lag.

The RTD measurement is ratiometric on a 0.1% metal film resistor, verified in an ice bath, lead compensated. Overkill, but something to do on days when I can't ski.

And I don't know if they used the same paint in 1980, or in 1880.

The official SF temp is measured in Dolores Park. The park has been extensively remodeled and re-landscaped in recent years, and the Stevenson box, up on a pole, has been moved.

within a

or

Weather and climate (really the same thing) seem to be chaotic at all time scales.

Martin Brown schrieb:

Hello,

but there is some IR from the sun too. IR was first discovered within sunlight.

There is also a different microclimate within large and dense towns and the surrounding open landscape with no houses.

Bye

John Larkin schrieb:

Hello,

but in my example with the thickness of ice in winter here there was no chaos at all. When they used natural ice for the brewing, they had thick ice nearly every year. In the last decades we had thick ice only very few years.

Bye

There's tons of IR reradiated from stuff on the ground, or trees, or buildings. And most paint is nearly black at those wavelengths.

The Stevenson box should be IR reflective (gold plated!) and have a big exhaust fan, but it's too late now.

But temperature variations have periodic and random noise components that vary from hours to millions of years.

Although that is true the inbound amount is small enough that ground and wall based reradiation of thermalised visible light beats it comfortably in daytime. At night it is a different matter although the only people who care are the military and professional astronomers.

The former don't want their nice rectangular tanks being cold or hot sitting ducks for FLIR imaging, and the latter don't want the outer surface of the dome supercooling by radiative losses and pouring cold air in through the dome slit causing dome turbulence.

In the old days domes were painted with the whitest paint that was physically possible to minimise daytime solar thermal loading. Active aircon changed it so that more modest whites were OK.

Astronomers now have a solution with not quite white paints containing some aluminium which makes it thermally neutral after dark and using a little more active cooling inside the building. Military is classified.

Indeed but the aim is to measure the air temperature. And white painted wooden slats of a Stevenson box are much better for that than you think. They are double louvred which you cannot see from outside.

It is not uncommon to have a rather large unstable temperature gradient in the air if the ground is newly illuminated by sunlight in still air. Glider pilots exploit the phenomenon in a very obvious way.

Absolutely not! It wants to be whitish with a hint of aluminium to remove the night time bias, but I don't know if they do that as all historical data will have been with the approved standard paint.

An IR reflective surface is also a very bad IR radiator and a thin metallic surface in direct sunshine and still air will get insanely hot. The odd stupid sunbather has been cooked to death by wrapping themselves in aluminium foil. Space blanket for cold weather survival exploits the ability of gold to prevent thermal IR losses.

You want the enclosure to let air pass freely but reflect away as much visible sunlight as possible and to be nearly black in the thermal IR.

of Five, Study Finds

That's a good point because it recognizes that once nature is tipped the gl obal environment is going to move to a new quasi equilibrium point which ma y not be all that hospitable to human or other life forms. The trend can be quantified without any assumptions about what's causing it, don't see wher e that enters the equation especially since mankind most likely isn't going to be able to do anything about it. The big question is how volatile the w eather becomes as it settles into the new equilibrium. Right now it's looki ng like the U.S. alone needs to budget about $200B annually for emergency r elief to victims of violent weather and you can expect this number to grow.

That will make it overheat in the daytime from re-radiated/downshifted sunlight, and cool at night by radiation to the sky. Instant climate extremes!

That is why astronomers prefer a grey night time profile. But Stevenson did not have access to modern nano pigments so he did his best.

The original Stevenson box has some limitations but it is a *lot* better than you are giving it credit for. I think you probably could pick out a slight systematic bias if you compared a modern astronomers dome painted Stevenson screen against the classical one but the difference would be small compared to the air temperature being measured in all but a handful of unusual low windspeed cases.

The main problem is that the true air temperature can vary wildly with distance off the ground and colour of the ground in still air conditions. Wet bare ground is much darker and warms up faster.

Five, Study Finds

environment is going to move to a new quasi equilibrium point which may not be all that hospitable to human or other life forms. The trend can be quantified without any assumptions about what's causing it, don't see where that enters the equation especially since mankind most likely isn't going to be able to do anything about it. The big question is how volatile the weather becomes as it settles into the new equilibrium. Right now it's looking like the U.S. alone needs to budget about $200B annually for emergency relief to victims of violent weather and you can expect this number to grow.

Oh, good grief. How's the Al Gorezeeria network coming, Al?

Often these internet sites use consumer grade weather stations. It isn't like every weather sensor is instrument grade.

It is item 41446, if the link doesn't work. ;-)

John Larkin schrieb:

Hello,

you would need a paint which is reflective for IR and visible light also. Gold is not reflective for the whole visible spectrum, therefore its color.

What about an experiment with several RTD sensors at different places. Then you can compare the temperatures at the different places?

Here is an experiment with different paints used for a Steevenson screen:

Bye

OK, white slats on the outside and a gold plated can inside, and a fan to pull up air from below, over the RTD. Sort of like the aspirated air temp sensor in your link.

The S box looks really bad:

They hadn't invented latex paint until maybe 1960-ish, so maybe that alone explains observed global warming.

Are you aware that there are a second set of louvred slats inside the box. But yes. Basically you want the outer facing surfaces of the slats brilliant white in the visible and near IR band but maximally dark in the thermal IR band characteristic of typical ambient temperatures. The inwards facing ones would ideally be surface mirror finish to prevent thermal radiation (but would have to be well insulated from the wood).

Aluminium foil would be about the cheapest internal metallic finish and it would help. As would a thin layer of low mass thermal insulator to decouple the metallic surface from the wood bulk temperature.

But this would alter an long established measurement tradition which despite its flaws provides a reasonable measure of air temperature.

It systematically reads high when in full sunlight and always has done - that is no surprise to anyone except you.

Only in your fevered imagination.