A comparison of bowen ratio and eddy correlation sensible and latent heat flux measurements above deciduous forest

Barr, Alan G.; King, Kenneth; Gillespie, T. J.; Hartog, G. Den; Neumann, H. H.

doi:10.1007/bf00709218

Cited by 99 publications

(66 citation statements)

References 27 publications

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“…There are numerous studies reporting a lack of energy closure (e.g. Aubinet et al 2000;Barr et al 1994Barr et al , 2006Bernhofer 1992;Bernhofer and Vogt 1999;Blanford et al 1991;Blanken et al 1998;Finch and Harding 1998;Jarvis et al 1997;Kabat et al 1997;Laubach 1996;Malhi et al 2002;Oncley et al 2007;Twine et al 2000;Wilson et al 2002;Wilson and Baldocchi 2000). Wilson et al (2002) found an imbalance in the order of 20% for a number of FLUXNET sites.…”

Section: Introductionmentioning

confidence: 99%

Available energy and energy balance closure at four coniferous forest sites across Europe

Moderow

Aubinet

Feigenwinter

et al. 2009

Theor Appl Climatol

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The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J H , latent heat J E , heat storage of biomass J veg and heat storage due to photosynthesis J C were of minor importance during day but of some importance during night, where J veg turned out to be the most important one. Comparisons of calculated storage terms (J E , J H ) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m −2 (10-11 W m −2 for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m −2 (approximately 6 W m −2 for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone.

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Section: Introductionmentioning

confidence: 99%

Available energy and energy balance closure at four coniferous forest sites across Europe

Moderow

Aubinet

Feigenwinter

et al. 2009

Theor Appl Climatol

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“…10), T a the difference in air temperature between two heights (K) and e a the difference in actual vapour pressure between the two heights (kPa). However, when gradients are very small, the adiabatic lapse rate cannot be neglected (Barr et al, 1994). Therefore the potential temperature should be used instead:…”

Section: Theorymentioning

confidence: 99%

Technical note: Using distributed temperature sensing for Bowen ratio evaporation measurements

Schilperoort

Coenders-Gerrits

Luxemburg

et al. 2018

Hydrol. Earth Syst. Sci.

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Abstract. Rapid improvements in the precision and spatial resolution of distributed temperature sensing (DTS) technology now allow its use in hydrological and atmospheric sciences. Introduced by Euser et al. (2014) is the use of DTS for measuring the Bowen ratio (BR-DTS), to estimate the sensible and latent heat flux. The Bowen ratio is derived from DTS-measured vertical profiles of the air temperature and wet-bulb temperature. However, in previous research the measured temperatures were not validated, and the cables were not shielded from solar radiation. Additionally, the BR-DTS method has not been tested above a forest before, where temperature gradients are small and energy storage in the air column becomes important.In this paper the accuracy of the wet-bulb and air temperature measurements of the DTS are verified, and the resulting Bowen ratio and heat fluxes are compared to eddy covariance data. The performance of BR-DTS was tested on a 46 m high tower in a mixed forest in the centre of the Netherlands in August 2016. The average tree height is 26 to 30 m, and the temperatures are measured below, in, and above the canopy. Using the vertical temperature profiles the storage of latent and sensible heat in the air column was calculated.We found a significant effect of solar radiation on the temperature measurements, leading to a deviation of up to 3 K. By installing screens, the error caused by sunlight is reduced to under 1 K. Wind speed seems to have a minimal effect on the measured wet-bulb temperature, both below and above the canopy. After a simple quality control, the Bowen ratio measured by DTS correlates well with eddy covariance (EC) estimates (r 2 = 0.59). The average energy balance closure between BR-DTS and EC is good, with a mean underestimation of 3.4 W m −2 by the BR-DTS method. However, during daytime the BR-DTS method overestimates the available energy, and during night-time the BR-DTS method estimates the available energy to be more negative. This difference could be related to the biomass heat storage, which is neglected in this study.The BR-DTS method overestimates the latent heat flux on average by 18.7 W m −2 , with RMSE = 90 W m −2 . The sensible heat flux is underestimated on average by 10.6 W m −2 , with RMSE = 76 W m −2 . Estimates of the BR-DTS can be improved once the uncertainties in the energy balance are reduced. However, applying, for example, Monin-Obukhov similarity theory could provide independent estimates for the sensible heat flux. This would make the determination of the highly uncertain and difficult to determine net available energy redundant.

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“…He concluded that unrealistically large and positive horizontal gradients in temperature and humidity would be needed for advective flux divergences in order to explain the EBC problem at half-hourly timescale. Other potential reasons for the imbalance discussed in the literature relate to the possible loss of low-and/or high-frequency components (Wolf et al, 2007;Sakai et al, 2001;Barr et al, 1994). A small fraction of the energy balance gap may also be explained by energy storage in the canopy and photosynthetic energy flux.…”

Section: K Imukova Et Al: Energy Balance Closure On a Winter Wheat mentioning

confidence: 99%

“…Oppositely, the LE flux post-closure method assigns the lacking energy fully to LE (Falge et al, 2005). The BR post-closure method assumes that the energy residual has the same Bowen ratio (Bo = H / LE) as the measured turbulent fluxes (Twine et al, 2000;Barr et al, 1994). In this case, the adjusted LE flux (LE * , Wm −2 ) is computed as follows:…”

Section: K Imukova Et Al: Energy Balance Closure On a Winter Wheat mentioning

confidence: 99%

Energy balance closure on a winter wheat stand: comparing the eddy covariance technique with the soil water balance method

et al. 2016

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Abstract. The energy balance of eddy covariance (EC) flux data is typically not closed. The nature of the gap is usually not known, which hampers using EC data to parameterize and test models. In the present study we crosschecked the evapotranspiration data obtained with the EC method (ET EC ) against ET rates measured with the soil water balance method (ET WB ) at winter wheat stands in southwest Germany. During the growing seasons 2012 and 2013, we continuously measured, in a half-hourly resolution, latent heat (LE) and sensible (H ) heat fluxes using the EC technique. Measured fluxes were adjusted with either the Bowen-ratio (BR), H or LE post-closure method. ET WB was estimated based on rainfall, seepage and soil water storage measurements. The soil water storage term was determined at sixteen locations within the footprint of an EC station, by measuring the soil water content down to a soil depth of 1.5 m. In the second year, the volumetric soil water content was additionally continuously measured in 15 min resolution in 10 cm intervals down to 90 cm depth with sixteen capacitance soil moisture sensors. During the 2012 growing season, the H post-closed LE flux data (ET EC = 3.4 ± 0.6 mm day −1 ) corresponded closest with the result of the WB method (3.3 ± 0.3 mm day −1 ). ET EC adjusted by the BR (4.1 ± 0.6 mm day −1 ) or LE (4.9 ± 0.9 mm day −1 ) post-closure method were higher than the ET WB by 24 and 48 %, respectively. In 2013, ET WB was in best agreement with ET EC adjusted with the H postclosure method during the periods with low amount of rain and seepage. During these periods the BR and LE postclosure methods overestimated ET by about 46 and 70 %, respectively. During a period with high and frequent rainfalls, ET WB was in-between ET EC adjusted by H and BR post-closure methods. We conclude that, at most observation periods on our site, LE is not a major component of the energy balance gap. Our results indicate that the energy balance gap is made up by other energy fluxes and unconsidered or biased energy storage terms.

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A comparison of bowen ratio and eddy correlation sensible and latent heat flux measurements above deciduous forest

Cited by 99 publications

References 27 publications

Available energy and energy balance closure at four coniferous forest sites across Europe

Available energy and energy balance closure at four coniferous forest sites across Europe

Technical note: Using distributed temperature sensing for Bowen ratio evaporation measurements

Energy balance closure on a winter wheat stand: comparing the eddy covariance technique with the soil water balance method

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