Studies of the dry surface layer in a sand dune field. (2). Effects of soil temperature gradients on the water content profiles in the dry surface layer.

Abstract

The behavior of soil water in a dry surface layer of sand developing under temperature gradients was discussed and a model for the layer under nonisothermal steady conditions was formulated by extending our isothermal steady model (Kobayashi et al., 1986). To bear out the nonisothermal steady model, the effects of temperature gradient on the water content profiles in the layer were examined by comparing the difference in shape between the profiles obtained using our isothermal and nonisothermal models with the observed one; the calculated difference in shape was found to be in qualitative agreement with the observed one.A significant reason why the dry surface layer can be distinguished definitely from the moist underlayer during the developing process is the presence of a steep temperature gradient in the surface layer. With an increase in the gradient of temperature across the dry surface layer the gradient of water content in the lower part of the layer becomes steeper, that is, the moisture contrast between the dry surface layer and the moist underlayer becomes greater.