This may be partially due to low sun angles associated with latitude and the 24 hour day that Antarctica experiences in summer, along with snow albedo. I’m looking into the full paper and will have a follow up post later. See the map below, there are a lot of these AWS. As I’ve always said, if you don’t fully understand the micro-site conditions in which the measurements are made, and the instrumentation limitations, you can’t be certain of the data it produces.
Atmospheric temperature measurements biases on the Antarctic plateau
Christophe Genthon, Delphine Six, Vincent FavierLaboratoire de Glaciologie et Géophysique de l’Environnement, CNRS/UJF, Saint Martin, d’Hères, France
Matthew Lazzara, Linda KellerAntarctic Meteorological Research Center, University of Wisconsin-Madison, Madison, USA
Abstract
Observations of atmospheric temperature made on the Antarctic plateau with thermistors housed in naturally (wind) ventilated radiation shields are shown to be significantly warm biased by solar radiation. High incoming solar flux and high surface albedo result in radiation biases in Gill (multiplate) styled shields that can occasionally exceed 10°C in summer in case of low wind speed.
Although stronger and more frequent when incoming solar radiation is high, biases exceeding 8°C are found even when solar is less than 200 Wm−2. Comparing with sonic thermometers, which are not affected by radiation but which are too complex to be routinely used for mean temperature monitoring, commercially available aspirated shields are shown to efficiently protect thermistor measurements from solar radiation biases. Most of the available in situ reports of atmospheric temperature on the Antarctic plateau are from automatic weather stations that use passive shields and are thus likely warm biased in the summer. In spite of low power consumption, deploying aspirated shields at remote locations in such a difficult environment may be a challenge. Bias correction formulae are not easily derived and are obviously shield dependent. On the other hand, because of a strong dependence of bias to wind speed, filtering out temperature reports for wind speed less than a given threshold (about 4–6 ms−1 for the shields tested here) may be an efficient way to quality control the data, albeit at the cost of significant data loss and records biased towards high wind speed cases.
Received: May 13, 2011; Revised: August 01, 2011
=================================================================
h/t to the Hockey Schtick
Could this be the same effect that produces temp spikes in Eureka?
Do all of these nations employ the same defective thermometer housing I wonder? And since the optimum housing for thermometers has been settled for over a hundred years, it s curious that they could get it so wrong there. And would not be the same housing employed in the Arctic?
REPLY: I don’t know that the thermometer housing is “defective” but more likely simply used outside of its tested range. Passive gill shield housings are pretty much a de facto standard and only made by a handful of companies. I would expect most stations in the Antarctic AWS program to the the same shield, though the Arctic is likely more randomly mixed between different shield types. -Anthony
All of the tricks of the trade are utilized!. I’m surprised each thermometer doesn’t have someone assigned to it to periodically warm it with a match!
Well, if this is the case, it should be easily seen in the data that most of the recent “warming” would occur in the summer months. CO2 induced warming would have its greatest impact in winter months when the air is very dry (little water vapor) and CO2 accounts for a greater portion of the total greenhouse effect of the atmosphere. Is most (all?) of the recent “warming” occurring in the summer months?
Just something else not to include in the next IPCC fantasy report.
Sean Peake says:
August 10, 2011 at 11:21 am
Could this be the same effect that produces temp spikes in Eureka?
Sean, don’t know about the spikes, but having worked there many years ago, and any nice day and wind shifting from the north can give you warmer temps, as I have hiked north from the station and it was significantly warmer in the interior.
Pielke Sr. reports ERA 40 is overestimating Arctic temperatures too:
http://pielkeclimatesci.wordpress.com/2011/08/10/indictment-of-the-era-40-reanalysis-in-a-new-paper-erroneous-arctic-temperature-trends-in-the-era-40-reanalysis-a-closer-look-by-screen-and-simmonds-2011/
Doesn’t matter… The models show it’s warming, and as we’ve seen over and over again in Climate Science, models and extrapolations beat observations every time!
This upward temperature bias under low wind velocity conditions was also documented by the same group in http://www.climantartide.it/introduzione/2009-Genthon.pdf
Genthon, C., M. S. Town, D. Six, V. Favier, S. Argentini, and A. Pellegrini (2010), Meteorological atmospheric boundary
layer measurements and ECMWF analyses during summer at Dome C, Antarctica, J. Geophys. Res., 115, D05104,
doi:10.1029/2009JD012741
That article also compares measurements to the ECMWF analysis and finds the analysis has an upward temperature bias.
“It appears that the radiation shields used for automated weather stations there aren’t fully protecting the temperature sensor from solar radiation exposure, and as a result are creating a false warming signal.”
Is it a false warming signal, or a false warm signal? There is a difference …
I teach classes about heat transfer and thermodynamics. These are both topics that depend on accurate temperature measurement. My students are often surprised at the difficulty involved in getting temperature measured accurately even to something as coarse as plus or minus 0.5C. Even an ice/water bath may have a larger uncertainty.
The difficulties come from three sources: 1) manufacturing and calibration of instruments and the inevitable drift, 2) the vagaries of trying to adequately control three independent modes of heat transfer, and 3) proof that the measurement is representative of the domain claimed.
Of the five dimensions of measurement, temperature is the most challenging.
[Fixed, and insults snipped. ~dbs, mod.]
It must be warming look at all that ice…. (sarc)
Actually, this might not be limited to Antarctica and it might explain something really odd I have noticed in the NCDC “Climate at a glance” graphs.
If you graph temperatures since 1998 to 2011, you will notice a rather significant drop in temperatures. The thing is, NONE of that drop is recorded in summer temperatures. Temperatures in summer in CONUS since 1998 are flat, no trend. On the other hand, winter temperatures show a rather eye-popping drop of -3.27 degrees/decade and the trend has been fairly steady with winter temps the last two years well below the 1901-2000 2oth century average. Spring and fall temperatures show less of a downtrend.
I had been wondering for some time why all seasons would show a down trend except for Summer. Spring (-0.31F/decade) and Fall (-0.53F/decade) are pretty close in their trends.
If the design of these temperature sensors results in radiative heating of the sensor, that would explain why there is such a drastic departure between summer and winter temperature trends over that 13 year period.
REF: http://www.ncdc.noaa.gov/oa/climate/research/cag3/na.html
First Year To Display: 1998
Last Year To Display: 2011
Winter/Spring/Summer/Fall temperatures.
“As I’ve always said, if you don’t fully understand the micro-site conditions in which the measurements are made, and the instrumentation limitations, you can’t be certain of the data it produces.”
One is only as good as the tools they have to attempt measuring reality. I simply wish that the majority of climate scientists would realize that ‘the map is not the territory.’
What perecntage of the AWS sites in the Antarctic use these types of shields
and where are they located?
Does that map show all the AWS sites regardless of what type of shield they use or do all AWS use it, so we can infer that all the sites on the map are affected?
Just trying to get my head round the scale of the problem
“up to 10°C” – compared to what? Presumably true air temperature. If the old thermometers had a similar bias, then this wouldn’t contribute to a false warming, just that the temperature records are poor and too warm from sunny periods.
What’s the defect? I’d guess that either the low sun angle is getting light and heat into the thermometer area, or that sunlight reflecting off the white surface is getting lots of light past the shield.
I knew Antarctica was cooling
but found it difficult to find any relaible
non-biased weather stations.
It’s funny that what the IPCC/Hockey Team would consider ‘science’ seems to involve sidestepping what in other fields would be considered basic engineering and quality assurance.
If you have a sensor on an aircraft that produces inaccurate measurements in extreme conditions and you have a system that relies on that data, people die and careers are broken.
If you have a weather sensor that produces inaccurate measurements in extreme conditions and climate models rely on that data, you get piles of grant funding to prove mankind is screwing up the planet.
When all the “errors” are in the same direction, they are not errors.
@Ric – the long days may also just saturate the screening ability of the shield, or heat everything around it enough to radiate heat into the thermometer.
Of course, a good comparison is the south polar satellite record, at http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc. It shows cooling since December, 1978 of 0.06 degree-C per decade.
It would be interesting to compare summer-only temperatures with one of these newfangled units and a conventional Stevenson screen located nearby.
Or maybe compromise and place one of these newer sensors inside a Stevenson screen and see if it makes a difference?
crosspatch – I would say Urban Heat Island affect, my best guess anyway
Know matter how smart the people making the claims you always need to take into account the fact they could be dead wrong becasue they made a simply mistake in their data collection method. .