Formation condition of snow cover in Japan using AMeDAS data

Although a large number of studies have been made on the discrimination of rain and snow, it is not clear when the ground is covered by the snow. The purpose here is to investigate how a snow formation condition (in particular air temperature and relative humidity) changes by an area.

AMeDAS (Automated Meteorological Data Acquisition System ) data by the Japan Meteorological Agency were used. Elements of analysis were air temperature, relative humidity, snow depth, snowfall amount, and precipitation amount. Period of analysis was from December to March.

It was confirmed that the weather condition (air temperature and relative humidity when the ground begins to be covered with snow) varies according to an area. It was frequent mainly on the Sea of Japan side that the relative humidity lowered when the snow cover in the high air temperature was observed. In contrast, the Pacific side showed the snow cover at the comparative low air temperature without the snow cover being confirmed at the high air temperature. This area difference is likely to be the difference in snowfall pattern such as winter monsoon and extratropical cyclone. Next, it was confirmed that the air temperature when the ground begins to be covered with snow decreases with an increase in altitude. This is related to smaller snowfall particles with an increase in altitude. From this point we might go on to an even more detailed examination of the ground temperature when the ground begins to be covered with snow, because the formation of snow cover is also affected by a state of the ground.