[Relationship of pollen counts of Japanese cedar to weather factors in Isehara City, Kanagawa].

We investigated the relationship of pollen counts of Japanese cedar to 9 different weather factors including means of the highest, and lowest temperatures, variation in temperatures mean of the lowest humidity on a day, daily mean, maximum wind velocity and daily wind direction in 1991, 1992, 1993 and 1995 in Isehara City, Kanagawa Prefecture. The results were as follows: 1. In each year, the highest temperature and the mean humidity were statistically related to the maximum pollen counts of Japanese cedar in the air. 2. Mean pollen counts per day on the days that the wind from the southwest were much higher than on the days with wind from the south. 3. These wind directions coincided with the dense plantation areas of Japanese cedar trees around Isehara City. We concluded that in terms of accurate daily forecasting of pollen counts in the air in a certain area or city, it should be taken into consideration that the highest temperature, and mean humidity together with the wind direction from the area of dense population of Japanese cedar trees surrounding the area are closely related to the increased pollen count per day.