Eddy-Covariance Measurements

Mauder, Matthias; Foken, Thomas; Aubinet, Marc; Ibrom, Andreas

doi:10.1007/978-3-030-52171-4_55

Cited by 37 publications

(29 citation statements)

References 162 publications

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“…The tower and canopy specifications as well as the flux processing options are listed in Table S2. The flux data processing options included measurement value filtering and de‐spiking (Mauder & Foken, 2004), the planar‐fit wind coordinate rotation method of Wilczak et al (2001), low‐pass filter spectral correction (Massman, 2001), sonic temperature correction for humidity effects (van Dijk et al, 2004), air density fluctuations (WPL method of Webb et al, 1980), lag water vapour versus wind corrections (Foken et al, 2012; Horst & Lenschow, 2009), and additional quality control checks (Foken et al, 2004). The friction velocity ( u *) was also filtered to ensure only the measurements with sufficient turbulence were included in analysis.…”

Section: Methodsmentioning

confidence: 99%

Unravelling groundwater contributions to evapotranspiration and constraining water fluxes in a high‐elevation catchment

Ryken

Gochis

Maxwell

2022

Hydrological Processes

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Despite the importance of headwater catchments for the water supply of the western United States, these regions are often poorly understood, particularly with respect to quantitative understanding of evapotranspiration (ET) fluxes. Heterogeneity of land cover, physiography, and atmospheric patterns in these high‐elevation regions lead to difficulty in developing spatially‐distributed characterization of ET. As the largest terrestrial water flux behind precipitation, ET represents a significant fraction of the water budget for any watershed. Likewise, groundwater is the largest available freshwater store and has been shown to play a large role in the water balance, even in headwater systems. Using an eddy covariance tower in the East River Catchment, a Colorado River headwaters basin, we estimated water and energy fluxes in high‐elevation, complex systems to better constrain ET estimates and calculate overall water and energy budgets, including losses from groundwater. We used the eddy covariance method to estimate ET from years 2017 through 2019 at a saturated, riparian end‐member site. Owing to complexities in near surface atmospheric structure such as stable boundary layers over snowpack and shallow terrain driven flow from surrounding landscape features, energy flux and ET estimates were limited to the warm season when energy closure residuals from the eddy‐covariance system were reliably less than 30%, a threshold commonly used in eddy covariance energy flux estimation. The resulting ET estimations are useful for constraining water budget estimates at this energy‐limited site, which uses groundwater for up to 84% of ET in the summer months. We also compared East River ET magnitudes and seasonality to two other flux towers (Niwot Ridge, CO and Valles Caldera, NM), located in the Rocky Mountains. These data are useful for constraining ET estimates in similar end‐member locations across the East River Catchment. Our results show that groundwater‐fed ET is a significant component of the water balance and groundwater may supply riparian ET even during low‐snow years.

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Section: Methodsmentioning

confidence: 99%

Unravelling groundwater contributions to evapotranspiration and constraining water fluxes in a high‐elevation catchment

Ryken

Gochis

Maxwell

2022

Hydrological Processes

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“…In doing so, we applied time-lag compensation, linear detrending, double rotation approach (Baldocchi et al, 1988;Wilczak et al, 2001), density fluctuation compensation (Webb et al, 1980), spike removal (Papale et al, 2006), and other statistical tests (Vickers & Mahrt, 1997). Poor-quality data were flagged (Mauder & Foken, 2011) and removed. Data from the raft and shore stations were aggregated into one dataset by favouring data with the best quality criteria (Mauder et al, 2013).…”

Section: Turbulent Heat Fluxesmentioning

confidence: 99%

Characteristic time scales of evaporation from a subarctic reservoir

Pierre

Nadeau

Thiboult

et al. 2023

Hydrological Processes

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Water bodies such as lakes and reservoirs affect the regional climate by acting as heat sinks and sources through the evaporation of substantial quantities of water over several months of the year. Unfortunately, energy exchange observations between deep reservoirs and the atmosphere remain rare in northeastern North America, which has one of the highest densities of water bodies in the world. This study characterizes the dynamics of turbulent heat fluxes by analysing in‐situ observations of a compact and dimictic reservoir (50.69° N, 63.24° W) located in a subarctic environment. The reservoir is characterized by a mean depth of 44 m and a surface area of 85 km2. Two eddy covariance (EC) systems, one on a raft and one onshore, were deployed from 27 June 2018 to 12 June 2022. The thermal regime of the reservoir was monitored using two vertical chains of thermistors. Results indicate a mean annual evaporation rate of 590 ± 66 mm, which is equivalent to ≈51% of the annual precipitation, with 84% of the evaporation occurring at a high rate from August to freeze‐up in late December through episodic pulses. It was difficult to close the energy balance because of the magnitude and the large time lag of the heat storage term. To circumvent this problem, we opted to perform calculations for a year that started from the first of March, as the heat storage in the water column was at its lowest at that point and could thus be ignored. From June to December, monthly Bowen ratios increased from near‐zero negative values to about 1.5. After September, due to smaller vapour pressure deficits, latent heat fluxes steadily decreased until the reservoir had a complete ice cover. Opposite diurnal cycles of sensible and latent heat fluxes were revealed during the open water period, with sensible heat fluxes peaking at night and latent heat fluxes peaking in the afternoon.

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“…Both micrometeorological methods (AGM and EC) share additional limitations to those mentioned above, such as the need for a homogeneous upwind fetch to avoid local advection errors. They also require steady-state conditions and well-developed turbulence, with no change in vertical flux with height (Loubet et al, 2013;Mauder et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Field comparison of two novel open-path instruments that measure dry deposition and emission of ammonia using flux-gradient and eddy covariance methods

et al. 2023

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Abstract. Dry deposition of ammonia (NH3) is the largest contributor to the nitrogen deposition from the atmosphere to soil and vegetation in the Netherlands, causing eutrophication and loss of biodiversity; however, data sets of NH3 fluxes are sparse and in general have monthly resolution at best. An important reason for this is that measurement of the NH3 flux under dry conditions is notoriously difficult. There is no technique that can be considered as the gold standard for these measurements, which complicates the testing of new techniques. Here, we present the results of an intercomparison of two novel measurement set-ups aimed at measuring dry deposition of NH3 at half hourly resolution. Over a 5-week period, we operated two novel optical open-path techniques side by side at the Ruisdael station in Cabauw, the Netherlands: the RIVM-miniDOAS 2.2D using the aerodynamic gradient technique, and the commercial Healthy Photon HT8700E using the eddy covariance technique. These instruments are widely different in their measurement principle and approach to derive deposition values from measured concentrations; however, both techniques showed very similar results (r=0.87) and small differences in cumulative fluxes (∼ 10 %) as long as the upwind terrain was homogeneous and free of nearby obstacles. The observed fluxes varied from ∼ −80 to ∼ +140 ng NH3 m−2 s−1. Both the absolute flux values and the temporal patterns were highly similar, which substantiates that both instruments were able to measure NH3 fluxes at high temporal resolution. However, for wind directions with obstacles nearby, the correlations between the two techniques were weaker. The uptime of the miniDOAS system reached 100 % once operational, but regular intercalibration of the system was applied in this campaign (35 % of the 7-week uptime). Conversely, the HT8700E did not measure during and shortly after rain, and the coating of its mirrors tended to degrade (21 % data loss during the 5-week uptime). In addition, the NH3 concentrations measured by the HT8700E proved sensitive to air temperature, causing substantial differences (range: −15 to +6 µg m−3) between the two systems. To conclude, the miniDOAS system appears ready for long-term hands-off monitoring. The current HT8700E system, on the other hand, had a limited stand-alone operational time under the prevailing weather conditions. However, under relatively dry and low-dust conditions, the system can provide sound results, opening good prospects for future versions, also for monitoring applications. The new high temporal resolution data from these instruments can facilitate the study of processes behind NH3 dry deposition, allowing an improved understanding of these processes and better parameterisation in chemical transport models.

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Eddy-Covariance Measurements

Cited by 37 publications

References 162 publications

Unravelling groundwater contributions to evapotranspiration and constraining water fluxes in a high‐elevation catchment

Unravelling groundwater contributions to evapotranspiration and constraining water fluxes in a high‐elevation catchment

Characteristic time scales of evaporation from a subarctic reservoir

Field comparison of two novel open-path instruments that measure dry deposition and emission of ammonia using flux-gradient and eddy covariance methods

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