海洋性冷気流の農業地帯への影響

(2) 冷害時 (1980年) における勇払・石狩平野の気象の特徴

抄録

The relationships between wind directions and meteorological conditions in Yufutsu and Ishikari plains were reported in the previous paper. Among the four years (1978-1981) that have been analyzed in the former study, the rice yields on Hokkaido were good in 1978 and 1979, but poor in 1980 and 1981. Especially in 1980, it was poor crop caused by the cool summer wind blown from Okhotsk High, and the crop situation index was 81.
The meteorological conditions in 1980 for Yufutsu and Ishikari plains were compared with those in 1978, 1979 and 1981 in this study. The methods of analysis are the same as those in the previous paper; the wind types were defined by wind directions and were classified three airflow patterns using AMeDAS data from May to August.
The monthly frequency of Pacific Ocean airflow for each year and the comparison of main wind types in Pacific Ocean airflow during August were shown in Figs. 1 and 2, and also, the monthly mean temperature and mean time of sunshine for an hour were shown in Table 1.
The following results were summarized;
1) The total occurrence of Pacific Ocean airflow (SSS*) in 1980 was the maximum but the difference among four years was not so large.
2) The occurrence of Pacific Ocean airflow during August of 1980 is less than those of 1979 and 1981, nevertheless the summer damage in 1980 was caused by low temperature of August.
3) The SSSN wind type in Pacific Ocean airflow has the highest frequency in August of 1980, on the other hand, the SSSS wind type is the fewest.
4) The monthly mean temperature and mean time of sunshine for an hour in August of 1980, while Pacific Ocean airflow flew through Yufutsu and Ishikari plains, were the lowest among four years, but in the other months of 1980 they were not.
Items 1) and 2) are different from the results reported for Tohoku Area that the year of cool summer damage has many frequencies of North-East wind, and also different from the present analysis for Tohoku Area shown in Table 2. The reason is that there are many frequency of Pacific Ocean airflow in Yufutsu and Ishikari plains every year because of topographical features, so that the frequency do not increase specially in cool summer year. It is recognized that few sunshine hour by low temperature causes a frequent occurrence of SSSN wind type instead of SSSS wind type.