Fig. 1. (a) Ratio of the amplitude of soil heat flux at the reference depth (A_r) to the amplitude of the soil heat flux at the surface (A₀) as a function of reference depth for three values of thermal diffusivity (); (b) difference between the time of maximum heat flux at the reference depth (t_r) and time of maximum heat flux at the soil surface (t₀) as a function of reference depth.