This paper just published in the AMS Journal of Atmospheric and Oceanic Technology has some broad ramifications for the claim (Steig et al, covered here) that Antarctica is warming. 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. The authors find that the summer Sun heats the shield for the electronic thermometers causing the warm bias that appears during the summer, which can be exacerbated by low wind conditions.
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
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