Intercomparison Experiment for Anemometers in Snowfall Season in Hokuriku Region, Japan

In wet snowfall region such as Hokuriku region in Japan, we sometimes faced the missing data for wind speed and direction measurement due to snow accretion and freezing on the anemometers. We have carried out the inter-comparison experiment for the anemometers, the propeller vane anemometer without heater and the sonic anemometers with heater in snowfall season in Hokiruku region Japan. The purpose of this study is to clarify the tolerance for snow accretion and measurement feature of anemometer under snowfall condition based on this experiment. We conducted the experiment from 12 December 2014 to 15 January 2015 at the experimental field (37.42 N, 138.88E, altitude 97m) in Snow and Ice Research Center, National Institute for Earth Science and Disaster Prevention in Nagaoka City, Japan. We deployed the sonic anemometer (model SA-10, Sonic), all-in-one sonic anemometer (model WS-600-UMB, Lufft) and propeller vane anemometer (model 05103, Young). We have put the instruments at the same height (3.5m) to eliminate the effect of height difference of each instrument. Also, we have set the instruments perpendicular to the prevailing wind to avoid the mutual interference of instruments. In addition, we put the monitoring camera for the eyesight check of snow accretion on the instruments. During the extreme snowfall from 12 to 15 December 2014, the snow depth increased by 113cm (from 10cm to 123cm). The air temperature varied from -2.3 deg. C to +1.6 deg. C while the wind speed observed by sonic anemometer varied 0.16 m/s to 3.2 m/s. The all-in-one sonic anemometer showed 0 m/s from 5:00 14 December to 15 December while the propeller vane anemometer showed 0 m/s from 1:30 to 9:20 on 13 December and from 17:00 13 December to 6:40 15 December. When the propeller vane anemometer and all-in-one sonic anemometer showed 0 m/s, the wind speed by the sonic anemometer varied from 0.5 m/s to 1.0 m/s. It is likely that the propeller vane anemometer and all-in-one sonic anemometer stopped operation due to the snow accretion and frozen ice, which was confirmed by the monitoring camera. The propeller vane anemometer doesn't have the heater. Although the all-in-one sonic anemometer has the heater, it was not sufficient under such severe snowfall condition. When the propeller vane anemometer and all-in-one sonic anemometer stopped their operation, the snow depth increased rapidly and the air temperature dropped below 0 deg. C. After the several hours from the air temperature increased above 0 deg. C, the propeller vane anemometer restarted its operation. The all-in-one sonic anemometer operated longer than the propeller vane anemometer during snow accumulation as it has the heater to prevent the snow accretion. However, the timing for restarting operation after snow melting delayed compared to the propeller vane anemometer. As the measurement path of sonic of the all-in-one sonic anemometer was located under the dome of the precipitation radar, hanged capping ice on this dome prevented the wind from reaching the measurement path of the sonic. Then, the restart of measurement was slower than the other instruments. In this study, we clarified the effect of the power and location of the heater of the anemometer on the missing data by the snow accretion and freezing on the anemometer. We found that the enough capacity and the appropriate location of the heater on the anemometer could prevent the missing data by the snow accretion and freezing on the anemometer. However, we need more experiment in the different climate and snow condition (e.g. Hokkaido, colder and light snow) to consider the effect of the heater for the anemometer.