Why the Thickness of the Dry Surface Layer in Sand Dune Fields Exhibits a Diurnal Variation?

Abstract

A dry surface layer usually forms in a sand dune field and it has an effect on the micro-climate. The thickness of the layer exhibits a diurnal variation with a maximum in the late afternoon and a minimum in the early morning. The thickness is a measure of the degree of dryness in the upper layers in sand dune fields; thus, the diurnal variation in the thickness suggests that there are large diurnal as well as irregular variations in the moisture conditions of the upper layers. The reason for the diurnal variation is that the rate of evaporation from the ground changes during the course of the day, while the upward water flux in the moist underlayer remains nearly constant throughout the day.