古記録を用いた京都の冬季気温の推定 Quantitative Estimates of Past Winter TemperaturesUsing Historic Documents and Diaries
Meteorological observations have been made since 1881 by a weather station in Kyoto, Japan. Therefore, some approach must be considered to know about tempe ratures before 1881. This paper gives quantitative estimates of the monthly mean of the lowest daily temperature in winter in Kyoto.<BR>A long record of dates Lake Suwa, in central Japan, 36°N138°E, 250km from Kyoto, was frozen has been found in the Suwa Shrine Documents by S. Fujiwara and collected by H. Arakawa.<BR>A long record of dates of snowfalls was extracted by the author from many old diaries kept in Kyoto.<BR>The dates Lake Suwa froze and the first and the last dates of snowfalls in Kyoto bet ween 1881 and 1953 are correlated with the monthly mean of the lowest daily temperature in winter observed in Kyoto. The correlations obtained are applied to estimate winter temperatures in Kyoto before 1881.<BR>As a result, two series of winter temperatures are obtained: one deduced from the freezing dates and the other from the dates of snowfalls. The former covers 430 years (1450-1880) and the latter 880 years (1001-1880).<BR>The two series give almost identical winter temperatures considering the error involved in the correlation used and the volume of available snowfalling data.<BR>The sequence of the 50-year means of temperature obtained from the dates the lake was frozen shows that the mean lowest daily winter (December-March) temperature has been rising incrementally from-0.7°C in 1551 to-0.2°C in 1880.<BR>The sequence of the 100-year means of temperature obtained from the dates of snowfalls shows that the mean of the lowest daily winter (December-March) temperature from the year 1101 to 1200 was higher by 0.8°C than one from the year 1001 to 1880.