Partial energy balance closure of eddy covariance evaporation measurements using concurrent lysimeter observations over grassland

Abstract. With respect to ongoing discussions about the causes of energy imbalance and approaches to force energy balance closure, a method has been proposed that allows partial latent heat flux closure (Widmoser and Wohlfahrt, 2018). In the present paper, this method is applied to four measurement stations over grassland under humid and semiarid climates, where lysimeter (LY) and eddy covariance (EC) measurements were taken simultaneously. The results differ significantly from the ones reported in the literature. We distinguish between the resulting EC values being weakly and strongly correlated to LY observations as well as systematic and random deviations between the LY and EC values. Overall, an excellent match could be achieved between the LY and EC measurements after applying evaporation-linked weights. But there remain large differences between the standard deviations of the LY and adjusted EC values. For further studies we recommend data collected at time intervals even below 0.5 h. No correlation could be found between evaporation weights and weather indices. Only for some datasets, a positive correlation between evaporation and the evaporation weight could be found. This effect appears pronounced for cases with high radiation and plant water stress. Without further knowledge of the causes of energy imbalance one might perform full closure using equally distributed weights. Full closure, however, is not dealt with in this paper.

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Partial energy balance closure of eddy covariance evaporation measurements using concurrent lysimeter observations over grassland

10.5194/hess-2020-299 ◽

2020 ◽

Author(s):

Peter Widmoser ◽

Dominik Michel

Keyword(s):

Energy Balance ◽

Eddy Covariance ◽

Strongly Correlated ◽

Energy Balance Closure ◽

High Radiation ◽

Time Intervals ◽

Plant Water Stress ◽

Energy Imbalance ◽

Partial Energy ◽

Semi Arid

Abstract. With respect to the ongoing discussion on the causes of the energy imbalance and approaches to force energy balance closure a method had been proposed which allows the partial latent heat flux closure (Widmoser and Wohlfahrt; 2018). In the present paper, this method is applied to four measurement stations over grassland under humid and semi-arid climate, where lysimeters (LY) and eddy covariance (EC) measurements were taken simultaneously. Results differ essentially from the ones quoted in literature. We distinguish between resulting EC-values weakly and strongly correlated to LY-observations as well as systematic and random deviations between LY- und EC-values. At the overall average, an excellent match could be achieved between LY and EC-measurements, which were partially closed with evaporation-linked weights. But there remain high differences between standard deviations of LY- and adjusted EC-values. For further studies we recommend data collected at time intervals even below half an hour. No correlation could be found between correction evaporation weights and weather indices. Only for some datasets a positive correlation between evaporation and the correcting evaporation weight could be found. This effect appears pronounced for cases with high radiation and plant water stress. Without further knowledge on the causes of energy imbalance one might perform full closure using equally distributed weights. Full closure, however, is not dealt with in this paper.

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Review of: Partial energy balance closure of eddy covariance evaporation measurements using concurrent lysimeter observations over grassland, by Peter Widmoser, Dominik Michel.

10.5194/hess-2020-299-rc2 ◽

2020 ◽

Author(s):

Anonymous

Keyword(s):

Energy Balance ◽

Eddy Covariance ◽

Energy Balance Closure ◽

Partial Energy

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Energy balance measurements over a banana orchard in the Semiarid region in the Northeast of Brazil

Pesquisa Agropecuária Brasileira ◽

10.1590/s0100-204x2009001100001 ◽

2009 ◽

Vol 44 (11) ◽

pp. 1365-1373 ◽

Cited By ~ 2

Author(s):

Carlos Antonio Costa dos Santos ◽

Bernardo Barbosa da Silva ◽

Tantravahi Venkata Ramana Rao ◽

Christopher Michael Usher Neale

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Eddy Covariance ◽

Heat Fluxes ◽

Irrigation District ◽

Semiarid Region ◽

Energy Balance Closure ◽

Wet Season ◽

Growing Seasons ◽

Eddy Covariance System

The objective of this work was to evaluate the reliability of eddy covariance measurements, analyzing the energy balance components, evapotranspiration and energy balance closure in dry and wet growing seasons, in a banana orchard. The experiment was carried out at a farm located within the irrigation district of Quixeré, in the Lower Jaguaribe basin, in Ceará state, Brazil. An eddy covariance system was used to measure the turbulent flux. An automatic weather station was installed in a grass field to obtain the reference evapotranspiration (ET0) from the combined FAO-Penman-Monteith method. Wind speed and vapor pressure deficit are the most important variables on the evaporative process in both growing seasons. In the dry season, the heat fluxes have a similar order of magnitude, and during the wet season the latent heat flux is the largest. The eddy covariance system had acceptable reliability in measuring heat flux, with actual evapotranspiration results comparing well with those obtained by using the water balance method. The energy balance closure had good results for the study area, with mean values of 0.93 and 0.86 for the dry and wet growing seasons respectively.

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Surface energy balance closure by the eddy-covariance method above three boreal forest stands and implications for the measurement of the CO2 flux

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2006.08.007 ◽

2006 ◽

Vol 140 (1-4) ◽

pp. 322-337 ◽

Cited By ~ 161

Author(s):

A.G. Barr ◽

K. Morgenstern ◽

T.A. Black ◽

J.H. McCaughey ◽

Z. Nesic

Keyword(s):

Energy Balance ◽

Surface Energy ◽

Boreal Forest ◽

Eddy Covariance ◽

Surface Energy Balance ◽

Co2 Flux ◽

Energy Balance Closure ◽

Forest Stands ◽

Eddy Covariance Method

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On the way to realistic large eddy simulations – A comparison of virtual measurements with CHEESEHEAD19 field measurements

10.5194/egusphere-egu21-2132 ◽

2021 ◽

Author(s):

Luise Wanner ◽

Sreenath Paleri ◽

Johannes Speidel ◽

Ankur Desai ◽

Matthias Sühring ◽

...

Keyword(s):

Energy Balance ◽

Eddy Covariance ◽

Field Measurements ◽

Transport Processes ◽

Large Eddy Simulations ◽

Surface Model ◽

Closure Problem ◽

Energy Balance Closure ◽

Large Eddy ◽

Eddy Covariance Measurements

<p>Large-eddy simulations are useful tools to study transport processes by mesoscale structures in the atmospheric boundary layer, since in contrast to single-tower eddy covariance measurements, they provide not only temporally but also spatially highly resolved information. Therefore, they are well suited to study the energy balance closure problem, for which the mesoscale transport of latent and sensible heat, triggered by heterogeneous ecosystems, is suspected to be a major cause. However, this requires simulations that are as realistic as possible and thus allow a comparison of real measurements in the field and virtual measurements in the simulation.<br>During the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD) experiment in the summer of 2019, a heterogeneous 10x10 square km domain was intensively sampled across scales. This data offers a unique possibility to set up large-eddy simulations with realistic surface heterogeneity. We use PALM to simulate two days and an area of 40 by 40 square kilometers incorporating the CHEESEHEAD site. The large scale atmospheric forcings to inform the boundary conditions are determined from the NCEP HRRR product. As the lower boundary condition, we use a soil and land-surface model coupled with a plant-canopy model, which we adapt to the CHEESEHEAD area based on ground-based and airborne measurements of plant physiological data.<br>In this study, we investigate how well the simulations match with real measurements by comparing simulated profiles and virtual tower measurements with field measurements from radiosonde ascents, lidar measurements of three-dimensional wind and water vapor, eddy-covariance measurements from the 400 meter tower in the center of the study domain, as well as from typical eddy-covariance stations distributed through the study area. This way, we investigate how realistic the simulations actually are and to what extent the knowledge gained from them concerning the energy balance closure problem can be transferred to field measurements.</p>

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Some aspects of the energy balance closure problem

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-4395-2006 ◽

2006 ◽

Vol 6 (12) ◽

pp. 4395-4402 ◽

Cited By ~ 197

Author(s):

T. Foken ◽

F. Wimmer ◽

M. Mauder ◽

C. Thomas ◽

C. Liebethal

Keyword(s):

Surface Layer ◽

Energy Balance ◽

Eddy Covariance ◽

Low Frequency ◽

Turbulent Fluxes ◽

Closure Problem ◽

Energy Balance Closure ◽

Considerable Influence ◽

Turbulence Spectrum ◽

Eddy Covariance Method

Abstract. After briefly discussing several reasons for the energy balance closure problem in the surface layer, the paper focuses on the influence of the low frequency part of the turbulence spectrum on the residual. Changes in the turbulent fluxes in this part of the turbulence spectrum were found to have a significant influence on the changes of the residual. Using the ogive method, it was found that the eddy-covariance method underestimates turbulent fluxes in the case of ogives converging for measuring times longer than the typical averaging interval of 30 min. Additionally, the eddy-covariance method underestimates turbulent fluxes for maximal ogive functions within the averaging interval, both mainly due to advection and non-steady state conditions. This has a considerable influence on the use of the eddy-covariance method.

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Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwestern Germany

Biogeosciences ◽

10.5194/bg-16-521-2019 ◽

2019 ◽

Vol 16 (2) ◽

pp. 521-540 ◽

Cited By ~ 4

Author(s):

Ravshan Eshonkulov ◽

Arne Poyda ◽

Joachim Ingwersen ◽

Hans-Dieter Wizemann ◽

Tobias K. D. Weber ◽

...

Keyword(s):

Energy Balance ◽

Eddy Covariance ◽

Wind Direction ◽

Climate Models ◽

Global Climate Models ◽

Energy Balance Closure ◽

Prevailing Wind ◽

Atmospheric Conditions ◽

Prevailing Wind Direction ◽

Wide Range

Abstract. The energy balance of eddy-covariance (EC) measurements is typically not closed, resulting in one of the main challenges in evaluating and interpreting EC flux data. Energy balance closure (EBC) is crucial for validating and improving regional and global climate models. To investigate the nature of the gap in EBC for agroecosystems, we analyzed EC measurements from two climatically contrasting regions (Kraichgau – KR – and Swabian Jura – SJ) in southwestern Germany. Data were taken at six fully equipped EC sites from 2010 to 2017. The gap in EBC was quantified by ordinary linear regression, relating the energy balance ratio (EBR), calculated as the quotient of turbulent fluxes and available energy, to the residual energy term. In order to examine potential reasons for differences in EBC, we compared the EBC under varying environmental conditions and investigated a wide range of possible controls. Overall, the variation in EBC was found to be higher during winter than summer. Moreover, we determined that the site had a statistically significant effect on EBC but no significant effect on either crop or region (KR vs SJ). The time-variable footprints of all EC stations were estimated based on data measured in 2015, complimented by micro-topographic analyses along the prevailing wind direction. The smallest mean annual energy balance gap was 17 % in KR and 13 % in SJ. Highest EBRs were mostly found for winds from the prevailing wind direction. The spread of EBRs distinctly narrowed under unstable atmospheric conditions, strong buoyancy, and high friction velocities. Smaller footprint areas led to better EBC due to increasing homogeneity. Flow distortions caused by the back head of the anemometer negatively affected EBC during corresponding wind conditions.

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Evaluation of Evapotranspiration from Eddy Covariance Using Large Weighing Lysimeters

Agronomy ◽

10.3390/agronomy9020099 ◽

2019 ◽

Vol 9 (2) ◽

pp. 99 ◽

Cited By ~ 8

Author(s):

Jerry Moorhead ◽

Gary Marek ◽

Prasanna Gowda ◽

Xiaomao Lin ◽

Paul Colaizzi ◽

...

Keyword(s):

Energy Balance ◽

Eddy Covariance ◽

Water Use ◽

Growing Season ◽

Irrigation Scheduling ◽

Error Rates ◽

Energy Balance Closure ◽

Crop Water ◽

Crop Water Use ◽

Hourly Data

Evapotranspiration (ET) is an important component in the water budget and used extensively in water resources management such as water planning and irrigation scheduling. In semi-arid regions, irrigation is used to supplement limited and erratic growing season rainfall to meet crop water demand. Although lysimetery is considered the most accurate method for crop water use measurements, high-precision weighing lysimeters are expensive to build and operate. Alternatively, other measurement systems such as eddy covariance (EC) are being used to estimate crop water use. However, due to numerous explicit and implicit assumptions in the EC method, an energy balance closure problem is widely acknowledged. In this study, three EC systems were installed in a field containing a large weighing lysimeter at heights of 2.5, 4.5, and 8.5 m. Sensible heat flux (H) and ET from each EC system were evaluated against the lysimeter. Energy balance closure ranged from 64% to 67% for the three sensor heights. Results showed that all three EC systems underestimated H and consequently overestimated ET; however, the underestimation of H was greater in magnitude than the overestimation of ET. Analysis showed accuracy of ET was greater than energy balance closure with error rates of 20%–30% for half-hourly values. Further analysis of error rates throughout the growing season showed that energy balance closure and ET accuracy were greatest early in the season and larger error was found after plants reached their maximum height. Therefore, large errors associated with increased biomass may indicate unaccounted-for energy stored in the plant canopy as one source of error. Summing the half-hourly data to a daily time-step drastically reduced error in ET to 10%–15%, indicating that EC has potential for use in agricultural water management.

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