Soil texture Coarse (sandy) soils conduct more heat, but have less heat capacity Fine-grained (clay) soils “hold onto” water

Heat Flow through Soil Vertical heat flux in soil or rock is down-gradient “diffusion” Formulate change in storage as a flux divergence: Combining heat flux with change in storage

Diurnal Variations of Soil Temperature Huge range near surface 25 K diurnal cycle at 0.5 cm Max T around 2 PM Damped and delayed with depth Only 6 K diurnal range at 10 cm’ Max T about 6 PM Negligible diurnal cycle at 50 cm Similar phenomena on seasonal time scales

Soil Temperature Variations Assume periodic forcing of period p (e.g., diurnal or seasonal cycles, ice ages, whatever). Response of T(z) is also periodic, but damped and delayed with depth relative to surface forcing “Penetration depth” (e-folding) of temperature oscillations forced by surface periodicity depends on period of forcing and physical properties of material p= 1 day D ~ 10 cm p= 1 yr D ~ 1.5 m p= 10,000 yr D ~ 150 m