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

Abstract

The sensitivity of climate simulations to diurnal variation in the 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 absolutely 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 that the net radiation and turbulent heat fluxes have phases identical to that of the soil surface temperature, we evaluate potential contributions of the wave phase difference to the surface energy balance closure. Results show that the sum of sensible heat flux and latent heat flux is always less than the available surface energy (i.e., the difference between net radiation and soil surface heat flux) even if all energy components are accurately measured, their footprints are strictly matched, and all corrections related to measurement environments and techniques are made. The energy balance closure ratio is extremely sensitive to the ratio of soil surface heat flux amplitude (A4) to net radiation flux amplitude (A1), and a high value of A4/A1 causes a significant failure in surface energy balance closure. An experimental case study confirms the theoretical analysis.