Hanksville, UT USHCN climate monitoring station with Stevenson Screen - sited over a gravestone. Photo by surfacestations.org volunteer Juan Slayton
Posted on 1/22/2011, 11:39:06 PM by Ernest_at_the_Beach
or those that don’t notice, this is about metrology, not meteorology, though meteorology uses the final product. Metrology is the science of measurement.
Since we had this recent paper from Pat Frank that deals with the inherent uncertainty of temperature measurement, establishing a new minimum uncertainty value of ±0.46 C for the instrumental surface temperature record, I thought it valuable to review the uncertainty associated with the act of temperature measurement itself.
As many of you know, the Stevenson Screen aka Cotton Region Shelter (CRS), such as the one below, houses a Tmax and Tmin recording mercury and alcohol thermometer.
Hanksville, UT USHCN climate monitoring station with Stevenson Screen - sited over a gravestone. Photo by surfacestations.org volunteer Juan Slayton
They look like this inside the screen:
NOAA standard issue max-min recording thermometers, USHCN station in Orland, CA - Photo: A. Watts
Reading these thermometers would seem to be a simple task. However, that’s not quite the case. Adding to the statistical uncertainty derived by Pat Frank, as we see below in this guest re-post, measurement uncertainty both in the long and short term is also an issue.The following appeared on the blog “Mark’s View”, and I am reprinting it here in full with permission from the author. There are some enlightening things to learn about the simple act of reading a liquid in glass (LIG) thermometer that I didn’t know as well as some long term issues (like the hardening of the glass) that have values about as large as the climate change signal for the last 100 years ~0.7°C – Anthony
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This post is actually about the poor quality and processing of historical climatic temperature records rather than metrology.
My main points are that in climatology many important factors that are accounted for in other areas of science and engineering are completely ignored by many scientists:
Metrology is the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology. Believe it or not, the metrology of temperature measurement is complex.
It is actually quite difficult to measure things accurately, yet most people just assume that information they are given is “spot on”. A significant number of scientists and mathematicians also do not seem to realise how the data they are working with is often not very accurate. Over the years as part of my job I have read dozens of papers based on pressure and temperature records where no reference is made to the instruments used to acquire the data, or their calibration history. The result is that many scientists frequently reach incorrect conclusions about their experiments and data because the do not take into account the accuracy and resolution of their data. (It seems this is especially true in the area of climatology.)
Do you have a thermometer stuck to your kitchen window so you can see how warm it is outside?
Let’s say you glance at this thermometer and it indicates about 31 degrees centigrade. If it is a mercury or alcohol thermometer you may have to squint to read the scale. If the scale is marked in 1c steps (which is very common), then you probably cannot extrapolate between the scale markers.
This means that this particular thermometer’s resolution is1c, which is normally stated as plus or minus 0.5c (+/- 0.5c)
This example of resolution is where observing the temperature is under perfect conditions, and you have been properly trained to read a thermometer. In reality you might glance at the thermometer or you might have to use a flash-light to look at it, or it may be covered in a dusting of snow, rain, etc. Mercury forms a pronounced meniscus in a thermometer that can exceed 1c and many observers incorrectly observe the temperature as the base of the meniscus rather than it’s peak: ( this picture shows an alcohol meniscus, a mercury meniscus bulges upward rather than down)
Another major common error in reading a thermometer is the parallax error.
Image courtesy of Surface meteorological instruments and measurement practices By G.P. Srivastava (with a mercury meniscus!) This is where refraction of light through the glass thermometer exaggerates any error caused by the eye not being level with the surface of the fluid in the thermometer.
(click on image to zoom)
If you are using data from 100′s of thermometers scattered over a wide area, with data being recorded by hand, by dozens of different people, the observational resolution should be reduced. In the oil industry it is common to accept an error margin of 2-4% when using manually acquired data for example.
As far as I am aware, historical raw multiple temperature data from weather stations has never attempted to account for observer error.
We should also consider the accuracy of the typical mercury and alcohol thermometers that have been in use for the last 120 years. Glass thermometers are calibrated by immersing them in ice/water at 0c and a steam bath at 100c. The scale is then divided equally into 100 divisions between zero and 100. However, a glass thermometer at 100c is longer than a thermometer at 0c. This means that the scale on the thermometer gives a false high reading at low temperatures (between 0 and 25c) and a false low reading at high temperatures (between 70 and 100c) This process is also followed with weather thermometers with a range of -20 to +50c
25 years ago, very accurate mercury thermometers used in labs (0.01c resolution) had a calibration chart/graph with them to convert observed temperature on the thermometer scale to actual temperature.
Temperature cycles in the glass bulb of a thermometer harden the glass and shrink over time, a 10 yr old -20 to +50c thermometer will give a false high reading of around 0.7c
Over time, repeated high temperature cycles cause alcohol thermometers to evaporate vapour into the vacuum at the top of the thermometer, creating false low temperature readings of up to 5c. (5.0c not 0.5 it’s not a typo…)
Electronic temperature sensors have been used more and more in the last 20 years for measuring environmental temperature. These also have their own resolution and accuracy problems. Electronic sensors suffer from drift and hysteresis and must be calibrated annually to be accurate, yet most weather station temp sensors are NEVER calibrated after they have been installed. drift is where the recorder temp increases steadily or decreases steadily, even when the real temp is static and is a fundamental characteristic of all electronic devices.
Drift, is where a recording error gradually gets larger and larger over time- this is a quantum mechanics effect in the metal parts of the temperature sensor that cannot be compensated for typical drift of a -100c to+100c electronic thermometer is about 1c per year! and the sensor must be recalibrated annually to fix this error.
Hysteresis is a common problem as well- this is where increasing temperature has a different mechanical affect on the thermometer compared to decreasing temperature, so for example if the ambient temperature increases by 1.05c, the thermometer reads an increase on 1c, but when the ambient temperature drops by 1.05c, the same thermometer records a drop of 1.1c. (this is a VERY common problem in metrology)
Here is a typical food temperature sensor behaviour compared to a calibrated thermometer without even considering sensor drift: Thermometer Calibration depending on the measured temperature in this high accuracy gauge, the offset is from -.8 to +1c
But on top of these issues, the people who make these thermometers and weather stations state clearly the accuracy of their instruments, yet scientists ignore them! a -20c to +50c mercury thermometer packaging will state the accuracy of the instrument is +/-0.75c for example, yet frequently this information is not incorporated into statistical calculations used in climatology.
Finally we get to the infamous conversion of Degrees Fahrenheit to Degrees Centigrade. Until the 1960′s almost all global temperatures were measured in Fahrenheit. Nowadays all the proper scientists use Centigrade. So, all old data is routinely converted to Centigrade. take the original temperature, minus 32 times 5 divided by 9.
C= ((F-32) x 5)/9
example- original reading from 1950 data file is 60F. This data was eyeballed by the local weatherman and written into his tallybook. 50 years later a scientist takes this figure and converts it to centigrade:
60-32 =28
28×5=140
140/9= 15.55555556
This is usually (incorrectly) rounded to two decimal places =: 15.55c without any explanation as to why this level of resolution has been selected.
The correct mathematical method of handling this issue of resolution is to look at the original resolution of the recorded data. Typically old Fahrenheit data was recorded in increments of 2 degrees F, eg 60, 62, 64, 66, 68,70. very rarely on old data sheets do you see 61, 63 etc (although 65 is slightly more common)
If the original resolution was 2 degrees F, the resolution used for the same data converted to Centigrade should be 1.1c.
Therefore mathematically :
60F=16C
61F17C
62F=17C
etc
In conclusion, when interpreting historical environmental temperature records one must account for errors of accuracy built into the thermometer and errors of resolution built into the instrument as well as errors of observation and recording of the temperature.
In a high quality glass environmental thermometer manufactured in 1960, the accuracy would be +/- 1.4F. (2% of range)
The resolution of an astute and dedicated observer would be around +/-1F.
Therefore the total error margin of all observed weather station temperatures would be a minimum of +/-2.5F, or +/-1.30c…
The physicist cited in the article was clear in stating that since the atmosphere varies by about half a degree a year, there was no valid way to assess cause for changes at that magnitude. IOW, a change of half a degree would be considered random error.
This of course was published before psychotics like James Hansen made hysteria into a scientific cottage industry.
GOOD POST....send to EVERY member of Congress and to the honchos at NASA and the bean counters at the United Notions....
One possibility is that the thermometer is radiating heat to the surrounding environment, or conversely, the surrounding environment is radiating heat into the thermometer. Heat is transferred by three methods: convection, conduction, and radiation. Assuming the thermometer is isolated from any conduction errors, its reading is effected by convection from the surrounding air, and also radiation to and from any surrounding surfaces.
For instance, depending on the emissivity of the bulb, a thermometer surrounded by a white painted box will read significantly different from an open thermometer which can radiate heat to the near absolute zero temperature of outer space on a clear night.
There is no place in Minnesota tonight reporting temps above zero....The whole damn State...
Normsrevenge posted a thread where it was down to 46 below near Int Falls....
Meanwhile here we will have Santa Ana winds tonight...some areas around 3 am will have the wind howling at 70 mph....temps tomorrow up to 76 df.....
Hansen and his crew routinely fudge the data to get the numbers they want. They have been caught doing this, multiple times, but the press still reports what they say, as if they are a credible source.
Oh that would be great! Where do we get one of those? Anyone?
BTTT
Dang - I’m a Quality Engineer - why have I never thought about this? Also didn’t realize that global temperature data is still read manually - an R & R study would be very interesting. Any data that the warmists have at their disposal is probably useless even if they haven’t fudged it - whatever “change” exists might just be inspector and instrument error.
Glass is technically not a solid, but a supercooled liquid. It's equilibrium state is crystalline. My guess is that as micro-crystals begin to coalesce in the matrix, it inhibits diffusion, thus increasing internal stress of the matrix and increasing the elastic modulus of the glass. Increasing the modulus of the material changes its response to the expansion of the internal fluid that indicates the temperature, resisting its expansion and thus modifying the temperature reading.
Sorry to disagree with you Carry. The ‘glass as a supercooled liquid’ thing needs to be put to rest. Glass is an amorphous (i.e. non-crystalline) solid at room temperature. It has no measurable flow. Crystallization always causes the glass to fracture, rendering it useless.
Ever measured a window's thickness top and bottom after 50 years? It's flow, albeit very slow. It gets more brittle too.
The distinctions of which you speak is a matter of redefinition of terminology in order to incorporate a distinction in behavior (fracturing), not molecular structure of the "solid." The definition I gave you is according to Van Vlack's Elements of Material Science and Engineering, p127, published June 1980. You can "disagree" with him.
What is being measured appears to be utter crap. They are trying to come up with a figure of "average global temperature", and use that as a way of measuring "climate change".
The problem is that what really needs to be looked at is the effect of any climate change on people and the biosphere. You can have a change in temperate-zone weather that has hotter, crop destroying summers and milder winters, versus where summers stay the same and winters get milder, versus where the only change is milder winters in Canada and Siberia -- each of these changes may involve the same shift in "average global temp" but have vastly different effects on the human race, whether negative or positive.
Now that we disagree on something, let us not fall into the trap (used by ‘global warming’ fans) of trying to define reality without using the scientific method. Can you post a link to a scientific study which verifies ‘measurable flow’ at room temperature? Or which verifies changes in ‘hardness’ over time? The brittleness you refer to may easily be a result of chemical weathering, which occurs due to exposure to water and other chemicals in the air. Weathering causes microscopic changes in the surface of the glass, making it easier to break. Not quite the same as brittleness, but close.
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