scholarly journals Supplementary material to "Source Partitioning of H<sub>2</sub>O and CO<sub>2</sub> Fluxes Based on High Frequency Eddy Covariance Data: a Comparison between Study Sites"

2018 ◽  
Author(s):  
Anne Klosterhalfen ◽  
Alexander Graf ◽  
Nicolas Brüggemann ◽  
Clemens Drüe ◽  
Odilia Esser ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
Supplementary Material ◽  
Study Sites ◽  
Source Partitioning

scholarly journals Source partitioning of H<sub>2</sub>O and CO<sub>2</sub> fluxes based on high-frequency eddy covariance data: a comparison between study sites

2019 ◽  
Vol 16 (6) ◽  
pp. 1111-1132 ◽  
Author(s):  
Anne Klosterhalfen ◽  
Alexander Graf ◽  
Nicolas Brüggemann ◽  
Clemens Drüe ◽  
Odilia Esser ◽  
...  
Keyword(s):  
Soil Respiration ◽  
Eddy Covariance ◽  
High Frequency ◽  
Canopy Height ◽  
Canopy Density ◽  
Partitioning Methods ◽  
Site Characteristics ◽  
Measurement Height ◽  
Study Sites ◽  
Source Partitioning

Abstract. For an assessment of the roles of soil and vegetation in the climate system, a further understanding of the flux components of H2O and CO2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands, and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H2O and CO2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modifications of both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulence characteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height). We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO2 fluxes was less robust than for H2O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration–evaporation events, performed satisfactorily, but did not result in significant advantages compared to the original method versions developed by Thomas et al. (2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated negatively with the ratio between measurement height and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristics that increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08.

scholarly journals Source Partitioning of H<sub>2</sub>O and CO<sub>2</sub> Fluxes Based on High Frequency Eddy Covariance Data: a Comparison between Study Sites

2018 ◽  
Author(s):  
Anne Klosterhalfen ◽  
Alexander Graf ◽  
Nicolas Brüggemann ◽  
Clemens Drüe ◽  
Odilia Esser ◽  
...  
Keyword(s):  
Soil Respiration ◽  
Eddy Covariance ◽  
High Frequency ◽  
Canopy Height ◽  
Canopy Density ◽  
Partitioning Methods ◽  
Site Characteristics ◽  
Measurement Height ◽  
Study Sites ◽  
Source Partitioning

Abstract. For an assessment of the role of soil and vegetation in the climate system, a further understanding of the flux components of H2O and CO2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied the source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high frequency eddy covariance measurements of twelve study sites including various ecosystems (croplands, grasslands, and forests) in a number of countries. Both partitioning methods are based on higher-order statistics of the H2O and CO2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08 including slight modifications of both approaches. Further, we analyzed the interrelations between turbulence characteristics, site characteristics (such as plant cover type, canopy height, canopy density and measurement height), and performance of the partitioning methods. We could identify characteristics of a data set as prerequisite for a sufficient performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO2 fluxes was more irregular than of H2O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at leaf-level, which is needed as an input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature and WUE could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration/evaporation events, performed satisfactorily, but did not result in significant advantages compared to the other method versions (developed by Thomas et al., 2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated negatively with the ratio between measurement and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. It was found, that all site characteristics which increase dissimilarities between scalars enhance partitioning performance for SK10 and TH08.

Supplementary material to "Potential evaporation at eddy-covariance sites across the globe"

2018 ◽  
Author(s):  
Wouter H. Maes ◽  
Pierre Gentine ◽  
Niko E. C. Verhoest ◽  
Diego G. Miralles
Keyword(s):  
Eddy Covariance ◽  
Potential Evaporation ◽  
Supplementary Material

scholarly journals Superior Oblique Myokymia Presumed Due to Large Posterior Fossa Arteriovenous Malformation

2020 ◽  
Vol 47 (6) ◽  
pp. 824-825
Author(s):  
Laura Donaldson ◽  
Brian van Adel ◽  
Amadeo R. Rodriguez
Keyword(s):  
High Frequency ◽  
Previous History ◽  
Ocular Motility ◽  
Slit Lamp ◽  
Primary Position ◽  
The Past ◽  
History Of ◽  
Supplementary Material ◽  
The Brain ◽  
Superior Oblique

A 26-year-old female presented with a complaint of intermittent oscillopsia and binocular vertical diplopia for the past 5 years. Over the past several months, she had noticed intermittent pulsatile tinnitus. She was otherwise healthy with no previous history of trauma and had no other visual or neurologic complaints. In Neuro-ophthalmology clinic, she was found to have 20/15 vision in both eyes with full ocular motility. There was a small exophoria in primary position and small esophoria in downgaze. Her slit lamp and fundus examinations were normal. During the assessment, the left eye was noted to undergo high-frequency, small amplitude incyclotorsional oscillations for a few seconds at a time (Video 1 in the supplementary material), which she was able to provoke by looking down. The diagnosis of superior oblique myokymia was made, and an MRI/MRA of the brain was requested.

scholarly journals Operative Use of Eddy Covariance Measurements: Are High Frequency Data Indispensable?

2013 ◽  
Vol 19 ◽  
pp. 293-302 ◽  
Author(s):  
D. Masseroni ◽  
C. Corbari ◽  
A. Ceppi ◽  
C. Gandolfi ◽  
M. Mancini
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
High Frequency Data ◽  
Frequency Data ◽  
Eddy Covariance Measurements

scholarly journals Measurements and quality control of ammonia eddy covariance fluxes: a new strategy for high-frequency attenuation correction

2019 ◽  
Vol 12 (11) ◽  
pp. 6059-6078 ◽  
Author(s):  
Alexander Moravek ◽  
Saumya Singh ◽  
Elizabeth Pattey ◽  
Luc Pelletier ◽  
Jennifer G. Murphy
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Attenuation Correction ◽  
High Frequency ◽  
Direct Method ◽  
Time Response ◽  
Trace Gas ◽  
Horizontal Wind ◽  
Nh3 Adsorption ◽  
Flux Loss

Abstract. Measurements of the surface–atmosphere exchange of ammonia (NH3) are necessary to study the emission and deposition processes of NH3 from managed and natural ecosystems. The eddy covariance technique, which is the most direct method for trace gas exchange measurements at the ecosystem level, requires trace gas detection at a fast sample frequency and high precision. In the past, the major limitation for measuring NH3 eddy covariance fluxes has been the slow time response of NH3 measurements due to NH3 adsorption on instrument surfaces. While high-frequency attenuation correction methods are used, large uncertainties in these corrections still exist, which are mainly due to the lack of understanding of the processes that govern the time response. We measured NH3 fluxes over a corn crop field using a quantum cascade laser spectrometer (QCL) that enables measurements of NH3 at a 10 Hz measurement frequency. The 5-month measurement period covered a large range of environmental conditions that included both periods of NH3 emission and deposition and allowed us to investigate the time response controlling parameters under field conditions. Without high-frequency loss correction, the median daytime NH3 flux was 8.59 ng m−2 s−1 during emission and −19.87 ng m−2 s−1 during deposition periods, with a median daytime random flux error of 1.61 ng m−2 s−1. The overall median flux detection limit was 2.15 ng m−2 s−1, leading to only 11.6 % of valid flux data below the detection limit. From the flux attenuation analysis, we determined a median flux loss of 17 % using the ogive method. No correlations of the flux loss with environmental or analyser parameters (such as humidity or inlet ageing) were found, which was attributed to the uncertainties in the ogive method. Therefore, we propose a new method that simulates the flux loss by using the analyser time response that is determined frequently over the course of the measurement campaign. A correction that uses as a function of the horizontal wind speed and the time response is formulated which accounts for surface ageing and contamination over the course of the experiment. Using this method, the median flux loss was calculated to be 46 %, which was substantially higher than with the ogive method.

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