海洋性冷気流の農業地帯への影響

勇払・石狩平野の風向と気象の特徴

抄録

The Yufutsu and Ishikari plains which are main agricultural areas in Hokkaido extend from the Pacific Ocean coast to the Japan Sea coast (8km width, 39km length) at an altitude below 50 meters (named low plain land). Meteorological conditions of the low plain land are characterized by sea winds imported from both the Pacific Ocean and the Japan Sea.
The theme of this paper is to analyze the meteorological conditions as related to the wind directions in Yufutsu and Ishikari plains.
The hourly wind directions from May to August were defined as shown in Fig. 3 and were summed up as wind types for period 1978-1981 (Table 1). The wind types in Table 1 were classified three airflow patterns; Pacific Ocean airflow, Japan Sea airflow, and Land & Sea airflow; based on the wind directions of Tomakomai, Naganuma and Ishikari, and shown in Table 1. The typical pattern in this low plain land is Pacific Ocean airflow which occurs in approximately 50% of all data. The SSSS wind type of Pacific Ocean airflow is the most frequent (about 32%). The appearances of Japan Sea airflow and Land & Sea airflow are 10 and 20%, respectively.
The temperature distributions for the representative wind types of each airflow pattern are shown in Fig. 4. The different characters of temperature distribution in the low plain land appear for each wind type. The SSSS, SSNS and SNNS wind types have a strong temperature gradient near the coasts. On the other hand, the NNNN has an almost homogeneous temperature distribution.
The hours of daylight and wind speed for each airflow pattern are shown in Table 2 and Table 3, and the meteorological conditions are summarized in Table 4. High wind speed, large temperature differences between the Pacific Ocean coast (Tomakomai) and the Japan Sea coast (Ishikari), and few hours of daylight characterize the SSSS wind type. The highest wind speed and many hours of daylight indicate in the NNNN wind type, and large temperature differences between the coastal areas and the middle of the low plain land accompanied by many hours of daylight characterize the SSNS and SNNS wind types. However, the climate in the low plain land becomes similar to the meteorological conditions of Pacific Ocean airflow because this pattern occurs the most frequently.
In Pacific Ocean airflow the advection fog flows from the Pacific Ocean to Tomakomai as shown in Table 5, indicating that it affects hours of daylight in the low plain land (Table 6).