A typical day in the Stevenson Screen Paint Test

Click for full sized image
Experiment config on July 13th. The screens were subsequently moved further apart. Note aspirated air temperature reference in forground.

I’ve been sorting through some of the data, and have found many similarities with many days of data. So I thought I’d present a typical day from this summer. The is 8/27/07, exactly one month after I started the experiment data logging.

I chose to show this day for starters because I can be certain that the whitewash was fully cured and no “newness effects” related to the conversion of CaOH to CaCO3 would remain. Whitewash cures by chemical reaction with air, not by drying.

First here is a 24 hour plot of the raw data, at 15 second sampling intervals, note that it gets noisy on the way to Tmax due to afternoon winds about 5-10 mph. Another factor for noises is that the response time of the NIST calibrated thermistors is fairly fast, in seconds.

paint-test-082707-raw-520.png
Full size graph: paint-test-082707-raw.png

Since it is harder to visually determine separate Tmax and Tmin with noisy data, I ran it though a data smoothing algorithm to produce this plot.

paint-test-082707-smoothed-520.png
Full size graph: paint-test-082707-smoothed.png

Here is the report from my data plotter on peaks for this graph:

Air Temp
Minimum = 55.38 at X = 8/27/2007 6:52:48 AM
Maximum = 95.04 at X = 8/27/2007 3:40:50 PM

Whitewash
Minimum = 56.22 at X = 8/27/2007 6:54:35 AM
Maximum = 96.94 at X = 8/27/2007 3:43:07 PM

Latex
Minimum = 55.92 at X = 8/27/2007 6:40:25 AM
Maximum = 97.74 at X = 8/27/2007 3:42:06 PM

Bare Wood
Minimum = 56.36 at X = 8/27/2007 6:39:24 AM
Maximum = 98.47 at X = 8/27/2007 3:42:36 PM

Since in regular use, COOP/USHCN stations report their daily max and min to NCDC for inclusion in the climatic database, I have provided zoomed graphs on the Tmax and Tmin periods.

Here is the zoomed Tmax graph:

paint-test-082707-tmaxzoom-520.png
Full size graph: paint-test-082707-tmaxzoom.png

And here is the zoomed Tmin graph:

paint-test-082707-tminzoom-520.png
Full size graph: paint-test-082707-tminzoom.png

As a secondary reference besides my own aspirated air temperature, I’m fortunate to have a CDF RAWS station within about 200 yards, on similar terrain and ground cover. It has a non-aspirated shield, and also has wind, and solar radiation among other sensors.

Here is the temperature plot from it:
temp-chi-raws-082707-520.png
Full size graph: temp-chi-raws-082707.png

A complete suite of plots, including wind and solar radiation in watts/m2 can be had from the CDEC data query web page.

As I wade though this data, I’ll be publishing additional days, and more detailed analyses, followed by a final report that covers everything that I’ve learned.

In the spring of 2008, I’ll be repeating this experiment at a slightly different location, there is a late afternoon bias for tree shading to the west that I want to remove from the experiment.

I’ll remind all readers that this is a single day, and that conclusions should not be drawn from it as it represents a single data point for Tmax/Tmin. Please be patient while I do further analysis.

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32 Responses to A typical day in the Stevenson Screen Paint Test

  1. Evan Jones says:

    Rev, would you clarify how the NOAA (et alia) calculate daily temps. Is it just an average of T-max and T-min (which you said they record) or is it a continual average. If it is the latter, there wouldn’tseem to be too much difference. But if it is the former, the difference could be quite pronounced. (Yes I realize this is only a one-day graph. “Patiently” awaiting long-term averages!)

    REPLY: As I understand it, the observer record the max and min daily temp, plus temp at time of observation on a small notepad form, then transcribes to a B91 form to mail in to NCDC. The observer rounds the max and min and observed temperature to the nearest whole number on the B91 form.

    NCDC takes the B91 form and transcribes into a computer database. From there (as I understand it) a daily average is created, and from those, yearly average which is what me most often see in climate studies. – Anthony

  2. jerry bono says:

    Jerry Bono

    I digitized the Chico points and took the average of 24 measures …. 78.14F.
    If we average the Tmax and Tmin we get 76.0F. That is 2.14 degrees lower than the integrated value and that is a lot . That is about 1.9C difference between the two methods. When was the B91 form put in place? If it was decades ago like in the 30′s then I can see why this was done, GW was not an issue then. If it is a recent invention then shame shame shame.

  3. jerry bono says:

    Looking at the zoomed Tmax, if we take the average Tmax for the three boxes and compare to the air temp, the boxes are 2.69F hotter than the air. Similarly, for Tmin, the boxes are an average 0.78F hotter. If this holds for these stations in general, then the daytime Tmax has 3 times the error than an early morning Tmin. It bothers me that the Tmax difference is so large.

    Is there any accounting for this?

  4. Sylvain says:

    If this is a typical day, which clearly shows a differences between each Stevenson screens only a few feet apart.

    This could mean that instrumental temp used around the world are really uncertain since their location are inconsistent (as shown with your other project surfacestations.org), sometimes moved around, with different type of instrument and their maintenance unknown.

    This could also mean that we are mislead by instrumental temp which don’t corroborate well with satellite, balloon and up to date proxies

  5. Robert Coté says:

    Could you possibly adopt a theme? “Stevenson Ranch” is catchy. We could make all kinds of snarky comments about stray heifers and bleached bones and such. The media would eat it up and unwittingly give venue to the opposition.

  6. George M says:

    The thermal mass of the enclosures appears to contribute a variable and erratic error in all cases. Makes one wonder if the housing of the reference thermistor has the same characteristic? Bottom line: We have no idea what the historical air temperature was, and it is difficult to envision a correction scheme which could exactly correct these errors to the accuracy the modelers seem to think we have.

  7. Evan Jones says:

    Thanks for the info, Rev.

    So, for this particular (summer) day, the T-Max/T-Min average was 0.51F warmer for latex than whitewash.

    T-max was 0.8 higher for latex at T-Max and 0.29F lower for T-min on that day.

    It will be interesting to see if this basic effect holds, and what the seasonal variance will be. (Whitewash weathering may well make all it harder to figure.)

  8. old whitguy says:

    keeping thermometers in boxes. that should give accurate temps measurements. yah.

  9. Fred says:

    More good in-put. I had an introduction to painting a SS in the mid 70′s. This experience was done mid-May. Others at higher elevation done later. Used latex exterior white (the kind that corroded thru the can bottom in 1 year). Frequent camping/jeepin trips to the Sierra Nevada allowed observations of other SS in State and National Forest applications. There were several stations that used white wash. My quess (of today) at these locations the supervisor was a purist. These must have been done annually, I always saw “well maintained” white washed units in July.

    I never gave this SS-temp a thought.

  10. CO2Breath says:

    Dude, you need to irrigate your yard! ;-)

  11. Chris D. says:

    Hi Anthony,

    Good to see you’re plowing forward on this project. It should provides some useful observations about the historic record. I had a couple of random questions occur to me as I was looking this over:

    1. Is this an effort to validate a previous study(s), or is this a new twist? (btw, you should publish either way, in this layman’s unsolicited opinion)

    2. Is the image of the CRSs facing south? (yes, you taught me well!)

    Godspeed, Anthony!

    REPLY:
    1. New study, AFIK no other researcher has done this type of test with 3 screens in parallel

    2. Yes the photo was taken looking south

  12. steven mosher says:

    One simple thing to look is a ‘simulation’ of what an observer would record for all three stations WRT Tmax and Tmin. That is scan though the daily data,
    record the Tmax and tmin, round as an observer would round and report
    out the measures, so if whitewash records a Tmax of 95.3F that’s recorded
    as 95, as an obsever would do. and if latex reports 95.6 for that day, then
    round to 96F as an observer would do. same for Tmin. It might make
    an instructive quick pass through the data.

    REPLY: Mosh, great suggestion!

  13. steven mosher says:

    Anthony, make sure you double check the rounding rules, I’m not sure
    what Noaa suggest for xx.5, futher when (tmax/tmin)/2 is calculated
    this figure is also rounded, JerryB and I once had a convo about this
    over on CA, he hasnt been around much, so you might have to go back
    to source data over at USHCN to figure out the rounding rule. My vague recollection was that they rounded UP at .5

  14. Evan Jones says:

    Come to think of it, if it’s rounded to whole numbers, you get a +1C at T-max and flat at t-min. So the plus-half-a -degree dif. actually comes in at a +1C.

    Hmmm.

  15. henry says:

    Evan Jones (22:45:12) said:

    “Come to think of it, if it’s rounded to whole numbers, you get a +1C at T-max and flat at t-min. So the plus-half-a -degree dif. actually comes in at a +1C.

    Hmmm.”

    I see his point. It’s possible that there is a “rounding bias” that may not be accounted for.

    It may not make a difference, but I’m seeing from .1-.4, round down, and from .5-.9, round up. That makes a +.1 rounding bias (4 readings would be rounded down, while 5 readings would be rounded up).

    Also, why have digital thermometers with an accuracy in tenths or hundredths, if you’re going to the nearest whole number?

  16. steven mosher says:

    nobody has paid much attention to the rounding bias. My QUICK glance at USHCN suggested an upward bias. However, if this rule is always followed, then there is no trend bias just a DC offset

  17. Evan Jones says:

    Actually, that comes out to an average +0.2C offset, using only T-Max/Min.

    Because we are not adding and then rounding, we are rounding, then adding.

  18. Evan Jones says:

    And I guess it’s a + 0.3C bias if you toss in TOBS.

    “Ah’m a headin’ fer the last roundup!”

  19. henry says:

    But wouldn’t this tend to put a “step” into the curves that Anthony posted, that is, a temp at 51 degrees (example) wouldn’t appear to change until a temp of 51.5 degrees is reached, then a step up to 52?

    Same on the low. A temp of 51 wouldn’t appear to drop until the temp reached 50.4, then a drop to 50.

    It would appear to “flat-top” the curves.

    Hope I’m making sense.

  20. Evan Jones says:

    Hmmm.

    Yes. But since they aren’t measuring continually, it doesn’t show up.

    Asi it is, measuring at three points gives three 10% opportunities for an upward bump.

    But as St. Mosh says, it’s an offset, not a trend.

  21. Evan Jones says:

    Unless methods have changed!

    Was there a time when only T-Min/Max was used? If so, adding TOBS would create a spurious +0.1C upswing in the record. (Or almost 15% of last century’s warming.)

  22. henry says:

    Not to keep beating this horse, but it’s appearing, at first glance, that the time of obs is being overridden.

    Here’s what I mean:

    Example: let’s say that the temp rises through 50.5. That would be raised to 51, at, say, 10am. If the temp never goes above 51.5, there will never be anything recorded over 51.

    If the temp reaches Tmax at noon, then drops below 50.4, then the recorded temp would be drop to 50 (at, say 2pm).

    That means, that no matter what the Tmax really was, you would have recorded a “window” of temps, not a “snapstot” of Tmax.

    The reading would be showing the temp of 51 from 10 am to 2 pm, and totally missing the Tmax.

    Maybe I’m just reading this too deep.

  23. Evan Jones says:

    Well you have to round it off somewhere.

    But it seems a bit crude to round to the nearest degree when one is spitballing over amounts less than the MoE.

    OTOH, I suppose one can get by with oversampling. But still …

  24. TCO says:

    There is a clear pattern of rushing to print with stuff that helps you and holding off with what hurts you. Why are you publishing one day only? If it’s non-representative, why is it shown? If it is representative, show that mathematically.

    I don’t trust you to pick a day at random. I think you will show stuff that helps your preconception preferentially.

    REPLY: TCO, its all coming, just not on the schedule you demand. I can’t do everything at once, and I don’t really care if you think you can’t trust me. That’s funny coming from you ….people who have interest and character, collaborate with me and reveal themselves. You don’t. You are still just another phantom with no name other than “TCO”. As far as I can tell your email and website are bogus. So don’t lecture me about trust please. Trust is a two way street, and you’ve provided nothing.

    Like I’ve said, I’m one man, with a business, a family, and many things to do. Doing this and the surfacestations.org project simultaneously on my own dime. Its a balancing act.

    When I get time there will be more, in the meantime please be patient. No wonder CA folks voted you “most irritating”.

  25. geoffrey french says:

    Rounding.
    I worked at the National Ocean Service/NOAA for 32 years. When I started, we used odd/even rounding, i.e., odd numbers round up, even round down. I even wrote my computer subroutines to round this way.
    95.5 = odd, round up = 96
    92.5 = even, round down = 92
    With large enough sample sizes, this should remove any round up bias.

    REPLY: True, but the NWS lets the observers do the rounding before recording the data, and it is unlcear if they use this method.

  26. dscott says:

    As I understand it, the observer record the max and min daily temp, plus temp at time of observation on a small notepad form, then transcribes to a B91 form to mail in to NCDC. The observer rounds the max and min and observed temperature to the nearest whole number on the B91 form.

    NCDC takes the B91 form and transcribes into a computer database. From there (as I understand it) a daily average is created, and from those, yearly average which is what me most often see in climate studies. – Anthony,

    So this isn’t even a weighted average to give a statisticly significant representation of the area? A weighted average using the hourly readings would give a more realistic representation of temperature. What you described here using a simple average to determine the climatic conditions is pretty much worthless data, IMO. Any conclusion based on this information will be as equally flawed as the data it is based upon. Just because you run it through a computer doesn’t enhance the data, in the business world we call this money laundering. Start with a false premise, apply flawless logic (computer), you end up with a flawlessly false conclusion. I am just disgusted with how far science has fallen, this wouldn’t have been acceptable even in the high school math classes of my day.

  27. Trevor says:

    Just to add another level of bias to the “rounding issue”:

    Say the digital thermometers have 0.1-degree precision. And say that the actual temperature is 74.45. If the obesrver knew what was there in the hundredths place, he would round this down to 74, because it’s clearly closer to 74 than to 75. But, if he’s looking at a digital thermometer that only has 0.1-degree precision, all he would see is 74.5 (74.45 rounded to the nearest 0.1 degree). The observer would round this up to 75 when he recorded it on the NCDC form. So, due to this “double-rounding” issue, not only is anything greater than or equal to x.5 degree being rounded up – anything greater than or equal to x.45 degree is being rounded up! This double-rounding issue quite clearly only works one way, because 74.54 would round up to 75 whether you rounded it directly or in two stages.

    But still, as long as the same equipment and rules were in place 30 years ago, the double rounding issue couldn’t account for any of the observed rise in temperature. However, 30 years ago, I suspect most thermometers were analog, mercury-bulb thermometers. Assuming they had marks at .5 degrees, even if the mercury level was at 74.49 degrees, a keen-eyed observer could still tell that the temperature was slightly below 74.5, and when he recorded the temperature on the form, he would round it down to 74.

    If, on the other hand, the analog thermometers did not have marks at .5 degrees, then there would be some range (its size depending on the eyesight of the observer, but lets say from x.45 to x.55) where the observer couldn’t tell whether it was closer to x or x+1. Though an individual observer might have a personal bias that made him consistently round such “close calls” one way (thus introducing bias for an individual station), you can make the assumption that, for every such observer, there’s another observer that consistently rounds the other way, and on average, there is no bias.

    Based on this analysis, I conclude that though individual analog thermometers probably have more bias (not to mention outright error) than individual digital thermometers, an average of a statistically-large-enough sample of analog thermometers clearly has less bias than that of digital thermometers. And that IS what we are looking at – an average of a huge sample of thermometers – when we say that “global average temperatures have increased by 0.6 degrees Celcius over the last 100 years”.

  28. Tim Doyle says:

    Then there’s the question of what are the equipment, procedures and practices used in other countries that might bias the data used for “global” averages.

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  30. Luke Davis says:

    Trevor,

    What you say is certainly true about analog thermometers–the short of it is, they’re rather precise, especially with a good reader.

    As for digital thermometers, I am not sure you’re right. When they give you a number, e.g. 79.5, it is not necessarily the case that any rounding at all has occurred. The measurement is likely +/- 0.1 degree (marked somewhere on either the thermometer or the manual that accompanied it). There is no reason to believe that the thermometer takes readings of 79.45 and rounds them (like a human would)–why couldn’t it just truncate? Or, perhaps it doesn’t take a measurement of the last decimal place in the first place–but +/- 0.1 from 79.45 means it could report either 79.4 or 79.5 and still be accurate within its defined precision.

  31. Trevor says:

    Luke:

    I don’t think I made myself very clear. I’m not claiming that the digital thermometer actually MEASURES hundredths of a degree, then, for some strange reason, reports in tenths of a degree. My point is that the thermometer is a tenth-of-a-degree approximation of an actual temperature, one that could be any of an infinite number of possible temperatures between 0.05 degrees below and 0.04999999… degrees above the reported temperature. I used x.45 as an example of the lowest possible fraction of a degree that could be reported as x.5 (and then rounded, by the observer, up to x+1). But x.454 would also be rounded up, as would x.46, x.49, x.451, x.4501, x.45001, and x.45000000000000001. The point is that, due to this double-rounding effect, actual temperatures between x.45 and x+1.44999999999… will always be rounded to x+1. Across a uniform probability distribution (which is obviously what temperatures, at this range of precision, are), the true average of temperatures in this range is x.95, not x+1, but the reported temperatures will all be x+1, and therefore the average of the reported temperature will be x+1. This means that there is, in addition to everything else, a positive 0.05 degree double-rounding bias that can be blamed on the use of digital thermometers that report temperature to the nearest tenth degree and observers that round those to the nearest whole degree.

    Let me try an example. Say you have 1,000 thermometers spread out over an area that varies in temperature by 10 degrees. And say that the ACTUAL temperature at each of these sites is defined as T(i) = 24+.01i, for i = 1 to 1,000, resulting in a uniform probability distribution between 24.01 and 34 degrees. The average temperature across all these stations can easily be shown to be exactly 29.005 degrees.

    But what is the average REPORTED temperature? Well, the first 44 sites (between 24.01 and 24.44) would all be reported as 24 degrees. The next 100 sites (between 24.45 and 25.44) would all be reported as 25. There would also be 100 sites reported as 26, 27, 28, 29, 30, 31, 32, and 33. And finally, there would be 56 sites (between 33.45 and 34.00) reported as 34 degrees.

    A weighted average of these reported temperatures would be [44(24)+100(25)+100(26)+100(27)+100(28)+100(29)+100(30)+100(31)+100(32)+100(33)+56(34)]/1000, or 29.06, which is 0.055 degrees higher than the ACTUAL average temperature over these stations. (This is actually slightly higher than the 0.05-degree bias I stated earlier, but only because I’m using a DISCRETE uniform probability distribution to approximate a CONTINUOUS uniform probability distribution. With a continuous uniform probability distribution, the resulting bias would be exactly 0.05 degrees.)

    Note that, if the thermometer reported temperature to the nearest WHOLE degree, though obviously less precise, it would nullify the double-rounding bias, resulting in a reported-average temperature of 29.01, just 0.005 off from the actual average (with a continuous probability distribution, even this small bias would completely disappear)

    If the thermometers have an error above and beyond the 0.05 measurement degrees that can be blamed on rounding only to the nearest tenth of a degree, that’s another issue. But the measurement error itself can never be more than 0.05 degrees for a device with a precision of 0.1.

    Unless, as you hypothesize, the device is merely truncating the temperature rather than rounding it. I don’t believe that is the case. But if it is, the measurement error wouldn’t be +/- 0.1 degree. It would be only MINUS 0.1 degree, i.e., the device-reported temperature would almost always be LESS THAN the actual temperature and would NEVER be more than the actual temperature (though on rare occasions, the two would be equal). I’m not sure, but I think that would cancel out the positive bias of the observer rounding. But again, there is no evidence that digital thermometers work that way.

  32. Richard Patton says:

    Evan, having been 20 years as a Navy ‘weather guesser’ I always thought that the standard method of determining the mean temperature for the day did not give an honest picture of what was happening. For example the following hourly temperature sequence from when I was at NAS Fallon NV in the Mid `80′s. (First observation at 1Am subsequent observations on the hour thereafter)
    14 13 13 13 13 14 14 15 17 18 20 21 21 20 20 20 19 19 18 18 18 20 32 45

    An inversion had been in place for a couple of weeks with the temperature 50′ above ground thirty degrees warmer than at the surface. Winds were dead calm throughout the day and kicked in near midnight to scour out the cold air.
    Taking the standard (Tmax+Tmin)/2 for the mean temperature of the day gives 29 degrees. Averaging the hourly observations yields 18.96 degrees, a considerable difference!

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