Influence of wave phase difference between surface soil heat flux and soil surface temperature on land surface energy balance closure

Abstract. The sensitivity of climate simulations to the diurnal variation in surface energy budget encourages enhanced inspection into the energy balance closure failure encountered in micrometeorological experiments. The diurnal wave phases of soil surface heat flux and temperature are theoretically characterized and compared for both moist soil and absolute dry soil surfaces, indicating that the diurnal wave phase difference between soil surface heat flux and temperature ranges from 0 to π/4 for natural soils. Assuming net radiation and turbulent heat fluxes have identical phase with soil surface temperature, we evaluate potential contributions of the wave phase difference on the surface energy balance closure. Results show that the sum of sensible heat flux (H) and latent heat flux (LE) is always less than surface available energy (Rn-G₀) even if all energy components are accurately measured, their footprints are strictly matched, and all corrections are made. The energy balance closure ratio (ε) is extremely sensitive to the ratio of soil surface heat flux amplitude (A₄) to net radiation flux amplitude (A₁), and large value of A₄/A₁ causes a significant failure in surface energy balance closure. An experimental case study confirms the theoretical analysis.