2022 Volume 131 Issue 4 Pages 393-405
Few studies have revealed the statistical tendencies of occurrences for cloud, fog, heavy rain or snowfall that characterizes mountain weather variabilities in Japan. Characteristics of seasonal and diurnal variations in fog and mist discriminated by visibility, precipitation types and precipitation intensity were clarified using data from November 2010 to October 2020 observed by Vaisala present weather sensor in the Sugadaira highland (1,320 m), Nagano Prefecture in Japan. Mist appeared more frequently than fog, and both increased in frequency at night. Fog prevailed in spring and autumn, while mist prevailed in the summer. In contrast, mist at the Nagano Local Meteorological Office (418 m) occurred frequently in the cold season and in the early morning. The frequency of snow and sleet decreased in the daytime. Sleet was infrequent but prevailed in December and March with the passing of south-coast cyclones and twin cyclones. The occurrence of freezing precipitation was very rare, but some intensive periods were found. Strong rain rates dominated from July to September, especially in the evening, and moderate and weak rain rates dominated in June or October when the Baiu front or typhoon prevails. There was no clear difference in seasonal/diurnal change depending on the snowfall intensity. The frequency for strong-intensity snowfall increased in cases of passing south-coast or twin cyclones. Instead of previous low-frequently visible observation, the characteristics derived by high-temporal long-term data could be utilized as validation data for satellite observation or numerical experiments.
