Air temperature measurements using autonomous self-recording dataloggers in mountainous and snow covered areas

摘要

High mountain areas are poorly represented by official weather observatories. It implies that new instruments must be evaluated over snow-covered and strongly insolated environments (i.e. mid-latitude mountain areas). We analyzed uncertainty sources over snow covered areas including: 1) temperature logger accuracy and bias of two widely used temperature sensors (Tinytag and iButton); 2) radiation shield performance under various radiation, snow, and wind conditions; 3) appropriate measurement height over snow covered ground; and 4) differences in air temperature measured among nearby devices over a horizontal band.The major results showed the following. 1) Tinytag performance device (mean absolute error: MAE approximate to 0.1-0.2 degrees C in relation to the reference thermistor) was superior to the iButton (MAE approximate to 0.7 degrees C), which was subject to operating errors. 2) Multi-plate radiation shield showed the best performance under all conditions ( 90% samples has bias between +/- 0.5 degrees C). The tube shield required wind ( 2.5 m s(-1)) for adequate performance, while the funnel shield required limited radiation ( 400 W m(-2)). Snow cover causes certain overheating. 3) Air temperatures were found to stabilize at 75-100 cm above the snow surface. Air temperature profile was more constant at night, showing a considerable cooling on near surface at midday. 4) Horizontal air temperature differences were larger at midday (0.5 degrees C). These findings indicate that to minimize errors air temperature measurements over snow surfaces should be carried out using multi-plate radiation shields with high-end thermistors such as Tinytags, and be made at a minimum height above the snow covered ground.