抄録
It is important to distinguish between solid and liquid in total precipitation events. In this study, wet-bulb temperature was used to estimate the percentage proportion of solid precipitation events. The wet-bulb temperature and the corresponding precipitation events were derived from meteorological data collected over the 10 years at 35 meteorological stations. Wet-bulb temperature was calculated from air temperature and vapor pressure data measured every three hours and the corresponding precipitation type was noted. Average threshold temperature below which more than 50% of total events are solid precipitation is 1.0ﾟC by the wet-bulb temperature, whereas it is 2.0ﾟC by air temperature. The range of the transition temperature thus defined is 0.6ﾟC to 1.5ﾟC by wet-bulb temperature. On the other hand, it is 1.0ﾟC to 2.9ﾟC by air temperature. In other words, transition of precipitation form takes place in a narrow temperature range when the wet-bulb is used. This is important because it makes it easier for us to use an average value to estimate precipitation forms for all the locations. The number of errors in which solid precipitation events were identified as rain or vice versa was reduced by half when wet-bulb temperature was used. It is therefore concluded that wet-bulb temperature is a more useful index than air temperature to estimate winter precipitation forms in Japan.
