2002 Volume 54 Issue 4 Pages 220-235
The purpose of this research study is to clarify the frequency of occurrence and spatial distribution of temperatures (a) below 0°C (<-0.1°C), (b) between 0°C and 3°C (0°C>and<2.9°C), and (c) over 3°C (>3.0°C) in the Hokkaido and Tohoku districts of northeastern Japan. During the winter, the Tohoku district has an isothermal line of 0°C. Hence, the author clarifies where the border between freezing and melting occurs within this district. At the same time, it is difficult to judge whether the precipitation between 0°C and 3°C is snowfall or rainfall.
AMeDAS (Automated Meteorological Data Acquisition Systems) were used to acquire the data. These automated observatories are installed at 330 points in the Hokkaido and Tohoku districts.
The period analyzed was 22 winters between 1979 and 2000. A winter season is defined as between December 1 of the previous year and March 31. During these four months, hourly observations were completed culminating in 2, 904 observations at each point. During leap years, there were 2, 928 observations. A frequency of 100% is defined as 2, 904 hours. The results are as follows.
(1) In the average year, the frequency of temperatures below 0°C was more than 70% in Hokkaido and 10 to 50% in the Tohoku district.
(2) The frequency of temperatures between 0°C and 3°C, varies from 0-9% in Hokkaido to 30-49% in the southwestern part of Tohoku in the average year. No stations recorded more than 50%.
(3) In the areas where temperatures occurred between 0°C and 3°C, some year-to-year changes were observed. During the 80's and 90's, 30 to 40% of this area shifted about 340km northward. However, there was no change in the location of the below 0°C temperatures.
(4) After calculating the frequency of temperatures over 3°C, each station was classified according to these 3 temperature ranges using a tri-linear diagram. This resulted in 10 weather-pattern regions for this area. In the Tohoku district, the spatial distribution is more complex than in Hokkaido.
