乾砂層内の温度日変化の新しい表現法

Abstract

On summer clear days, a dry surface layer with a depth of several centimeters is usually formed at sandy field. It is known that this dry surface layer has strong effects on microclimate near the surface, raising the surface temperature. This layer is called the “Kanshaso (dry sand layer)” in Japanese. Although the water content in this dry layer is extremely small, the water content below this dry layer is considerably larger than that in the above layer and approximately vertically uniform. There is, therefore, a sharp change in the water content between the top dry layer and the bottom moist layer. The contrast of soil moisture between the two layer affects necessarily the vertical conduction of heat in the sandy layer.In this report, a one dimensional equation for heat conduction was solved to obtain a new expression for the diurnal temperature change in the dry surface layer, by taking account of the diurnal change in the thermal diffusivity κ.The results obtained can be summarized as follows:1) The diurnal change in the temperature θ of the dry surface layer can be well approximated byθ=θ0+R1sin(ωt-γsinωt+e1)Where θ0 is the daily mean, R1 and e1 denote the amplitude and the phase lag of diurnal temperature wave, respectively, ω=2π/T is the time angle, and γ is a positive constant.2) The second item -γ sinωt in the sine function on the right hand side of the above equation shows the effect of the diurnal change in thermal diffusivity on the temperature wave in the dry surface layer.3) The newly obtained expression for the diurnal temperature change in the dry surface layer can be used to evaluate the thermal characteristics of surface dry layers.