Abstract
Precise estimation of surface-atmosphere exchange is a major challenge in micrometeorology. Previous literature presented the eddy covariance (EC) as the most reliable method for the measurements of such fluxes. Nevertheless, the EC technique is quite expensive and complex, hence other simpler methods are sought. One of these methods is Flux-Variance (FV). The FV method estimates sensible heat flux (H) using high frequency (~10Hz) air temperature measurements by a fine wire thermocouple. Additional measurements of net radiation (Rn) and soil heat flux (G) allow the derivation of latent heat flux (LE) as the residual of the energy balance equation. In this study, the Flux Variance method was investigated, and the results were compared against eddy covariance measurements. The specific goal of the present study was to assess the performance of the FV method for the estimation of surface fluxes along a variable fetch. Experiment was carried out in a tea garden; an EC system measured latent and sensible heat fluxes and five fine-wire thermocouples were installed towards the wind dominant direction at different distances (fetch) of TC1 = 170 m, TC2 = 165 m, TC3 = 160 m, TC4 = 155 m and TC5 = 150 m from the field edge. Footprint analysis was employed to examine the effect of temperature measurement position on the ratio between 90% footprint and measurement height. Results showed a good agreement between FV and EC measurements of sensible heat flux, with all regression coefficients (R2) larger than 0.6; the sensor at 170 m (TC1), nearest to the EC system, had highest R2 = 0.86 and lowest root mean square error (RMSE = 25 Wm−2). The estimation of LE at TC1 was also in best agreement with eddy covariance, with the highest R2 = 0.90. The FV similarity constant varied along the fetch within the range 2.2–2.4.
Highlights
Accurate estimation of surface-atmosphere exchanges of mass, energy, and momentum is a major challenge in micrometeorology
The flux variance (FV) estimations are based on the similarity constant (CT) that was adjusted to give the best agreement between HFV and
The effect of variable fetch on the performance of the FV method for the estimation of surface fluxes of H and latent heat flux (LE) in the open field was studied for the first time
Summary
Accurate estimation of surface-atmosphere exchanges of mass, energy, and momentum is a major challenge in micrometeorology. The estimation of ET has been a major research concern during the past few decades [1,2]. Atmosphere 2019, 10, 299 widely used for whole canopy latent (LE) and sensible heat flux (H) measurements [3,4,5]. The EC method is relatively expensive and complex, it is not available for day-to-day use by farmers, for irrigation management; it is mostly used as a research tool [6,7]. There is a need for developing a less complex and low-cost method. There are some well-established indirect ET estimation methods available, including surface renewal (SR) and flux variance (FV). The FV method, based on the principle of Monin Obukhov Similarity Theory (MOST), has been very popular and undergone a series of developments since its inception by Tillman in 1972 [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
