Combining surface renewal analysis and similarity theory:: A new approach for estimating sensible heat flux -: art. no. W05201

Castellvi et al. [2002] proposed a new approach for estimating sensible heat flux that combined surface renewal analysis and similarity theory. The approach used a calibration parameter ( here referred as beta) which was introduced by scaling the mean local gradient of air temperature with the ramp amplitude of air temperature over the mean volume of air parcel renewed per unit ground area, traditionally denoted as (alphaz), with z as the measurement height. Parameter b is explained and determined for half-hourly samples. It is shown that (kbeta) similar to 0.1 is appropriate under unstable conditions over a variety of canopies, with k as the von Karman constant. This value is rather robust with regard to height and when measuring in both the roughness and inertial sublayers. This understanding of parameter beta allowed a better understanding of parameter alpha and permitted the derivation of a modified approach for estimating sensible heat flux. In practice, it was possible to consider the new approach exempt from calibration. It was attractive for field applications and showed excellent performance under both stable and unstable conditions. A test was carried out for canopies where fetch requirements and full surface cover were not adequate. It was also shown that the flux variance method required calibration and did not perform as well as the proposed approach under such field conditions.