Cold and Warm Bias in a Weather Station

Early on in my project I got complaints like “why don’t you ever show a cooling bias?”. Problem was, there weren’t a lot of cold bias stations to show. Other than shading, and in one case in Washington state where the station was getting mist from a dam spillway, there just weren’t many examples. This also explains why “Eli Rabett” was never able to keep up his “cool station of the day” series that he started as a counter to my published photos (he used mine), some months ago.

Given human energy use, and artificial surfaces such as concrete, asphalt, and roofing tend to be near where many stations have been located, the bias has been predominantly warmer. Another reason the predominate bias is warm is that stations are often placed for the convenience of the observer, which means closer to human habitation.

So it was with some intrigue that I found this station yesterday, with the help of my very first volunteer, Russ Steele. The NOAA COOP station simultaneously demonstrates a cold bias and a warm bias. This is the infrared photo I took of it:

ir photo

The warm bias seem obvious, but can you guess what the cold bias is?

Ok if you didn’t guess it, don’t feel bad. Infrared photos don’t show detail well.

Here is the answer:

visible light photo

Snow on the roof of the shelter.

At the time, the sun had just passed below the tree line to the west, and the snow was melting. The cold melt water was dribbling down the slats on the rear of the Stevenson Screen shelter. You can see some of the slats are just a little bit darker in the IR photo. Of course any air passing through those slats would lose some heat to that water, cooling the air reaching the thermometer. The result would be a cool bias for daytime Tmax when the snow is melting, but only for as long as the snow is there. The effect would likely be greater on a warmer day with more sunshine as more snow melted.

You might say; “but all similar stations in the area would have snow on the roof, so the bias would be nearly equal and would be caught in adjustments.” Well….maybe. You see the problem is, the NWS doesn’t seem to have a published procedure for COOP observers related to snow removal from Stevenson Screens (At least none I’ve found, if you know of one please advise). So some observers might clean snow from the roofs, while others may not. So some stations in the area might have a cool bias, others may not. But how would you know? Note the square hole in the snow. That is for a snow depth board for which there are procedures.

This station has some other biases, one of which Russ and I are examining in detail. It turns out this particular station figures significantly into a peer reviewed paper. Stay tuned as we learn more from comparative measurements done in parallel with this station.

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Bill in Vigo
February 8, 2008 7:08 pm

Anthony I would assume that it is a pleasure to have to try to figure the amount of a cool bias for a change. I expect that there might be more than meets the eye on this one. Can’t wait to see the next post. Keep up the good work.
Added from other thread where it was misposted:
I so wish that I was in a position to help with the survey but alas some of the requirements aren’t available to us here in the rural areas of N E Alabama. they haven’t upgraded the network here for the high speed connection. Some times I think they pipe in sunshine.
Anthony I look forward with relish your analysis at the end of the survey.

February 8, 2008 10:09 pm

This is off topic but I thought it might be of interest to you:
It seems like the IPCC is adjusting the historical temps down as time goes on.

February 9, 2008 1:17 am

Raven, the link is broken. Also, there has been a persistent pattern of adjusting historical temperatures down to exaggerate the current warming. CA has documented multiple examples.

February 9, 2008 2:30 am

That is too bad the link was broken.
It overlaid a temp plot from TAR and another from AR4 and pointed out a number of differences.
You can see what they showed in AR4 Ch3 Figure 3.4 a)
The difference was caused by a change to the algorithm used to process SST.

An Inquirer
February 9, 2008 6:19 am

The link worked for me, but it was in a language I do not understand, probably French. Nevertheless, it was apparent that the graph was highlighting inconsistencies in the historical record.

Chris D.
February 9, 2008 8:35 am

To Bill: I’m pretty sure there is one site on the grounds of St. Bernard Abbey near Cullman that I have wanted to survey for quite a while but haven’t been able to make the trip. Anthony’s site has all the resources you need to locate and plan a survey of the site.
Anthony: I hope you are doing well. This post made me wonder – seeing that there were no footprints, is there also an MMTS on site? I have to also wonder if snow accumulates this way on MMTS, and whether a difference between the two would be yet another bias.

Evan Jones
February 9, 2008 11:24 am

No Not working. I suggest pulling it up in French (from R’s link), cut/pasting the line into Google and hit the “translate this page” option when the hit comes up.

February 9, 2008 3:37 pm

Accordng to AR4 someone came up with a theory that historical measurement techniques for SST temperature had a warm bias. They applied this fudge factor to the SSTs in AR4 and reduced the old temperatures.
Is anyone surprised that the IPCC was quick to correct data biases that makes GW look worse but completely ignores any evidence that the data is biased the other way?
I get nauseous anytime i read someone talking about the ‘quality’ of the IPCC reports.

peter vd berg
February 10, 2008 9:32 am

Living in france, he also complains that for 15 years British owner of the data (Climate Reseach Unit de l’Université d’East Anglia, Grande Bretagne, ) denied Peter Jones to publish this data. He just got a partial 2 weeks ago by way of a formal plaint, still they are arguing archive problems for the rest.

Jeff in Seattle
February 10, 2008 3:55 pm

A high speed Internet connection is not a requirement for this project at all. All that is needed is a camera, and optionally, a GPS. But we have ways around that too.

Uploading pics works fine on dial-up too, I did it for a long, long time. High speed just makes it faster.

Evan Jones
February 10, 2008 4:00 pm

What’s with this jealousy over data? Doesn’t it help a scientist, and also science if an institution’s data is made widely available. Doesn’t every time it is cited add prestige to the originator? I can understand proprietary interests, but this seems to go ‘way beyond that.

February 11, 2008 5:56 am

Any air moving over the wet slats would be cooled by evaporation as well as the cold water. Evaporative cooling could also be an issue following summer showers as well. I believe I read somewhere that some of the newer Stevenson screens are made out of plastic, not wood. Since plastic would absorb less water than wood. Especially if the paint (or whitewash) is not fresh, this could add yet another bias to the record.

February 12, 2008 8:51 am

I’m confused. You claim that current weather observing stations are biased, yet you make no comment on how these observations were taken historically. In the past, a lot of temperature records were taken on rooftops or in downtown settings. In my opinion, it would be more important to have a precise, standardized data set than an accurate one in gauging the effects of climate change. You seem to be suggesting that we introduce bias into the data set, by altering these stations. Doing so would compromise all the previous data gathered from them.
MODERATORS REPLY: The Baltimore station has already been “altered” by NOAA/NWS and was moved to street level in Baltimore. Note that the NWS did similar moves for rooftop stations in San Francisco, and Eureka, both of which I reported on. My view is that accurate AND contiguous records are the best indicator for the surface temperature record, not the mishmash of stations in wide measurement venues we currently have.
Apparently NOAA agrees, and has setup the new Climate Reference Network for that very purpose, though it will be awhile before enough data is gathered to show useful trends.

April 15, 2008 10:29 am

Hmmm, why are you hung up on air temperatures? Other than confusing the basic issues involved, what purpose would measuring air temperature (at ground surface) serve? Meditate on the meaning of latent heat instead…….

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