Estimating sensible heat flux over bare soils using surface renewal and similarity theories for unstable cases

Abstract A model to estimate the sensible heat flux half-hourly (H) for bare soils was derived based on surface renewal (SR) and similarity (MOST) theories, involving the land surface temperature (LST) and low-frequency measurements (wind speed and the air temperature in half an hour), HSR-LST. The dataset included semi-arid and arid climates, where the optimal surface roughness length for momentum (zom), determined from the actual friction velocity (u*) and the measurement height, ranged between 0.68 and 6.1 mm. Fixing the parameter kB-1 (=ln⁡(zom/zoh ) , where z0h is the roughness length for heat) to 2 (traditional value under neutral conditions), a non-dimensional relationship for the SR parameters was proposed. The sensible heat flux estimates were evaluated using the root mean square difference (RMSD) over the mean actual sensible heat flux (HEC), (E =RMSD/(HEC) 100%) considering (as a rule of thumb) excellent, good and moderate for E values up to 25%, 30% and 35%, respectively. For different measurement heights (ranging from 0.5 m up to 20 m), HSR-LST was in excellent, good, and moderate agreement in 6, 3 and 13 cases, respectively. Three cases had E value ranging between 37% and 39%. The sensible heat flux estimates using MOST required calibration of zom and kB-1. It is concluded that HSR-LST method is more direct requiring the wind speed, the air temperature and the land surface temperature as input.