The observational studies of the micro-climate in Ube-Ono tea garden, Yamaguchi, the warm part of Japan, were carried out throughout more than a year. The topographical feature of the experiment site is a conical hill with the elevation of the top 110m, the relative elevation 40m, the area 27ha, the inclination of the slopes 2-9 degrees, and the horizontal distance between the top and the lower part of the hillside 420m in the east. The relationships between the distribution of minimum air temperatures on the slopes and the height above sea level were analyzed for the year of 1980. Remarkable developments of inversion layer were found on the slopes.
Results are summarized as follows:
(1) The temperature difference of minimum air temperature between the top and the lower part of the hillside was the maximum value of 12°C and the average value of 4°C.
(2) Air temperature at the lower part fell below -10°C in winter, in spite of being considered as the warm region of Japan. In April and May, the minimum temperature fell below the freezing point and it was frosted over tea plants. But no frost was recorded on the slopes from the middle to the top in and after April.
(3) The distribution of minimum air temperatures on the slopes became a positive linear function of the height, that is, the inversion relationships were found in almost cases. On the other hand, temperature lapse was rarely found there in the reading system of the lowest value throughout the duration of 7-10 days.
(4) The value of the temperature gradient along the slopes changed with season and weather conditions from the largest value of 3.1°C·10m^-1 in late spring to the lowest value of -0.5°C·10m^-1 in summer. These seasonal changes of temperature gradient were caused by the change in the amount of effective radiation, and influenced secondly by the wind velocity.
(5) With a view to predicting the grade of temperature gradient along the slopes practically, it is suggested to use the relationship that the positive temperature gradient, or the grade of inversion becomes large as decreasing of relative humidity of the preceding day, under conditions of almost same air temperatures.
(6) Some injured tea plants in the lower parts and the bottom of the east slope were supposed to be caused by the cold air layer developed in winter.