On the use of the post-closure methods uncertainty band to evaluate the performance of land surface models against eddy covariance flux data

Abstract

Abstract. The energy balance of eddy covariance (EC) flux data is normally not closed. Therefore, at least if used for modelling, EC flux data are usually post-closed, i.e. the measured turbulent fluxes are adjusted so as to close the energy balance. At the current state of knowledge, however, it is not clear how to partition the missing energy in the right way. Eddy flux data therefore contain some uncertainty due to the unknown nature of the energy balance gap, which should be considered in model evaluation and the interpretation of simulation results. We propose to construct the post-closure methods uncertainty band (PUB), which essentially designates the differences between non-adjusted flux data and flux data adjusted with the three post-closure methods (Bowen ratio, latent heat flux (LE) and sensible heat flux (H ) method). To demonstrate this approach, simulations with the NOAH-MP land surface model were evaluated based on EC measurements conducted at a winter wheat stand in southwest Germany in 2011, and the performance of the Jarvis and Ball-Berry stomatal resistance scheme was compared. The width of the PUB of the LE was up to 110 W m −2 (21 % of net radiation). Our study shows that it is crucial to account for the uncertainty in EC flux data originating from lacking energy balance closure. Working with only a single post-closing method might result in severe misinterpretations in model-data comparisons.

Evaluation of energy balance closure adjustment methods by independent evapotranspiration estimates from lysimeters and hydrological simulations

“…To address the energy balance closure problem, several adjustment methods have been proposed in the literature (e.g., Foken et al, ; Ingwersen, Imukova, Högy, & Streck, ; Twine et al, ). The most prominent theory says that the underestimation in the energy balance derived with the EC approach originates from large‐scale transport not being captured and allocates the entire residual to the turbulent fluxes.…”

“…To address the energy balance closure problem, several adjustment methods have been proposed in the literature (e.g., Foken et al, 2011;Ingwersen, Imukova, Högy, & Streck, 2015;Twine et al, 2000).…”

High-resolution land surface fluxes from satellite and reanalysis data (HOLAPS v1.0): evaluation and uncertainty assessment

“…The energy imbalance for eddy-covariance measurements can be as high as 20 to 30 % on average (e.g., Wilson et al, 2002). The reason for this energy balance closure problem is still not fully understood and subject of ongoing research (e.g., Ingwersen et al, 2015). Several approaches have been developed to empirically correct for the energy closure (Foken et al, 2011;Twine et al, 2000;Wilson et al, 2002;Ingwersen et al, 2015).…”

“…The reason for this energy balance closure problem is still not fully understood and subject of ongoing research (e.g., Ingwersen et al, 2015). Several approaches have been developed to empirically correct for the energy closure (Foken et al, 2011;Twine et al, 2000;Wilson et al, 2002;Ingwersen et al, 2015). A simple energy balance correction (Bowen ratio method) is applied in this study following the approach as described in Twine et al (2000).…”

Eddy covariance based surface‐atmosphere exchange and crop coefficient determination in a mountainous peatland

“…Different methods have been proposed to solve this issue (e.g. Ingwersen, Imukova, Högy, & Streck, ); however, we decided to correct Q E by partitioning the energy balance residual (Δ Q ) according to the Bowen ratio β (Twine et al, ; Equation ) in order to adjust ET a . Using this closure procedure, we assume the scalar similarity of gas and heat exchange not only for small scale but also for large‐scale eddies (Foken, ; Mauder et al, ).…”