On the Temperature Well Water

Abstract

Over the past twenty and more years, the temperature of well water has been continuously observed in a well at the Mito Meteorological Station which is 10.50 m deep and has a diameter of 0.98m. These observed data are studied and the following results are obtained.
(1) The annual variation of temperature of well water is nearly parallel to that of the air temperature and presents a single maximum in August, a single minimum in February, au l its amplitude is 0.44°C, which does not come to 4% of the amplitude of air temperature.
(2) A secular variation is noticed for the temperature of well water. The difference between the temperature of well water and the soil temperature at the same depth correlates considerably with the Wolf's relative sun-spot number.
(3) Sudden changes of temperature of well water are chiefly due to rainfalls. When the diurnal precipitation exceeds 50mm, the effect of rainfall appears suddenly after a rainy day and approaches its maximum two or three days later, and its mean value becomes 0.5_??_0.7°C. Thus, the effect of rainfall acts upon the temperature of well water so as to make it low in winter and high in summer.
(1) and (2) are explained by the effect of air column with which the well is filled, and the (3) is determined by the difference between the temperature of raindrops and the temperature of well water and by the circumstances of permeation of raindrops into the soil.