A New Post‐Hoc Method to Reduce the Energy Imbalance in Eddy Covariance Measurements. Zhang, W., Nelson, J. A., Miralles, D. G., Mauder, M., Migliavacca, M., Poyatos, R., Reichstein, M., & Jung, M. Geophysical Research Letters, 51(2):e2023GL107084, January, 2024.
A New Post‐Hoc Method to Reduce the Energy Imbalance in Eddy Covariance Measurements [link]Paper  doi  abstract   bibtex   
Abstract Latent and sensible heat flux observations are essential for understanding land–atmosphere interactions. Measurements from the eddy covariance technique are widely used but suffer from systematic energy imbalance problems, partly due to missing large eddies from sub‐mesoscale transport. Because available energy drives the development of large eddies, we propose an available energy based correction method for turbulent flux measurements. We apply our method to 172 flux tower sites and show that we can reduce the energy imbalance from −14.99 to −0.65 W m −2 on average, together with improved consistency between turbulent fluxes and available energy and associated increases in r 2 at individual sites and across networks. Our results suggest that our method is conceptually and empirically preferable over the method implemented in the ONEFlux processing. This can contribute to the efforts in understanding and addressing the energy imbalance issue, which is crucial for the evaluation and calibration of land surface models. , Plain Language Summary Eddy covariance measurements are key to understanding the exchange of energy and water between the Earth's surface and the atmosphere, which helps us validate Earth system models that predict how the land interacts with the atmosphere. However, these measurements often show an energy imbalance problem, meaning that the measured turbulent energy does not fully account for all the energy entering the system. For two decades, scientists have been using advanced simulations and multi‐tower measurements to find out why this happens, and have found that the movements of airflow in a horizontal direction play a large role. Taking this knowledge into account, we propose a simple, data‐driven method to make these measurements more accurate. This new approach reduces the error not just at one eddy covariance site, but at multiple sites around the globe, and it's also effective at reflecting the energy changes that occur with daily weather events like rain. , Key Points Observed systematic imbalance of energy flux (∼17%) across the network of eddy covariance sites A theoretically motivated correction method based on available energy variations is proposed The available energy correction method has conceptual and empirical advantages compared to the method implemented in the ONEFlux pipeline
@article{zhang_new_2024,
	title = {A {New} {Post}‐{Hoc} {Method} to {Reduce} the {Energy} {Imbalance} in {Eddy} {Covariance} {Measurements}},
	volume = {51},
	issn = {0094-8276, 1944-8007},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL107084},
	doi = {10.1029/2023GL107084},
	abstract = {Abstract
            
              Latent and sensible heat flux observations are essential for understanding land–atmosphere interactions. Measurements from the eddy covariance technique are widely used but suffer from systematic energy imbalance problems, partly due to missing large eddies from sub‐mesoscale transport. Because available energy drives the development of large eddies, we propose an available energy based correction method for turbulent flux measurements. We apply our method to 172 flux tower sites and show that we can reduce the energy imbalance from −14.99 to −0.65 W m
              −2
              on average, together with improved consistency between turbulent fluxes and available energy and associated increases in
              r
              
                2
              
              at individual sites and across networks. Our results suggest that our method is conceptually and empirically preferable over the method implemented in the ONEFlux processing. This can contribute to the efforts in understanding and addressing the energy imbalance issue, which is crucial for the evaluation and calibration of land surface models.
            
          , 
            Plain Language Summary
            Eddy covariance measurements are key to understanding the exchange of energy and water between the Earth's surface and the atmosphere, which helps us validate Earth system models that predict how the land interacts with the atmosphere. However, these measurements often show an energy imbalance problem, meaning that the measured turbulent energy does not fully account for all the energy entering the system. For two decades, scientists have been using advanced simulations and multi‐tower measurements to find out why this happens, and have found that the movements of airflow in a horizontal direction play a large role. Taking this knowledge into account, we propose a simple, data‐driven method to make these measurements more accurate. This new approach reduces the error not just at one eddy covariance site, but at multiple sites around the globe, and it's also effective at reflecting the energy changes that occur with daily weather events like rain.
          , 
            Key Points
            
              
                
                  Observed systematic imbalance of energy flux (∼17\%) across the network of eddy covariance sites
                
                
                  A theoretically motivated correction method based on available energy variations is proposed
                
                
                  The available energy correction method has conceptual and empirical advantages compared to the method implemented in the ONEFlux pipeline},
	language = {en},
	number = {2},
	urldate = {2024-11-26},
	journal = {Geophysical Research Letters},
	author = {Zhang, Weijie and Nelson, Jacob A. and Miralles, Diego G. and Mauder, Matthias and Migliavacca, Mirco and Poyatos, Rafael and Reichstein, Markus and Jung, Martin},
	month = jan,
	year = {2024},
	pages = {e2023GL107084},
}
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