Eddy Covariance
Also known as: Eddy covariance, EC flux, Eddy correlation, Direct flux measurement
The eddy covariance method is a direct, micrometeorological technique that measures turbulent fluxes of momentum, heat, water vapor, and CO2 by computing the covariance between high-frequency fluctuations of wind velocity and scalar properties (temperature, humidity, concentration). It is the gold standard for measuring ecosystem-atmosphere exchanges and validating model parameterizations.
Key highlights
- Direct measurement without empirical transfer coefficients; based on fundamental conservation of mass and energy
- High temporal resolution resolves diurnal cycles and storm-scale variations in fluxes
- Simultaneous measurement of multiple scalar fluxes enables closure studies and process understanding
- Well-suited for heterogeneous surfaces and complex terrain where bulk methods fail
Intuition
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How it works
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When to use it
Use eddy covariance for direct measurement of ecosystem-atmosphere fluxes (net ecosystem production, evapotranspiration, momentum), for validation of land-surface models and parameterizations, for process studies of turbulence and transport, and for long-term monitoring in long-term ecological research sites.
Strengths & limitations
- Direct measurement without empirical transfer coefficients; based on fundamental conservation of mass and energy
- High temporal resolution resolves diurnal cycles and storm-scale variations in fluxes
- Simultaneous measurement of multiple scalar fluxes enables closure studies and process understanding
- Well-suited for heterogeneous surfaces and complex terrain where bulk methods fail
- High capital and maintenance costs; requires trained technicians for deployment and data quality control
- Sensors can drift or fail; calibration and validation are ongoing requirements
- Energy balance typically closes only to 70–80%; missing processes (storage, horizontal advection, mesoscale circulation) account for the gap
- Representative of a small footprint area (typically 10–100 m); extrapolation to larger scales requires caution
Common pitfalls
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Applications
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Frequently asked
Why do eddy covariance measurements not close the energy balance?
The gap (typically 10–30% of net radiation) is attributed to horizontal advection, mesoscale circulation, storage of heat and moisture in canopy/soil, and systematic instrument errors. Multiple studies suggest the gap reflects real physics not captured in local vertical measurements.
What is the WPL correction and why is it important?
The WPL (Webb-Pearman-Leuning) correction accounts for density fluctuations induced by heat and water vapor fluctuations affecting the measured vertical wind. This correction can exceed 10% of measured sensible and latent heat fluxes and must be applied consistently.
How do I choose the averaging period?
Standard practice is 30 minutes to 1 hour, which balances stationarity assumptions with ensemble averaging of turbulent eddies. Shorter periods (10–15 min) may be better in very weak-wind conditions; longer periods risk violating stationarity during transitions.
What is the footprint and how far downwind does eddy covariance measure?
The footprint—the upwind area contributing to measured fluxes—depends on stability, wind speed, and measurement height. Typical footprints extend 10–100 m upwind; under unstable conditions with strong vertical mixing, the footprint is larger.
Sources
- 1.Baldocchi, D. (2003). Assessing the eddy covariance technique for evaluating carbon dioxide fluxes of ecosystems: past, present and future. Global Change Biology, 9(4), 479-492.
- 2.Foken, T. (2006). The energy balance closure problem: An overview. Ecological Applications, 18(6), 1351-1367.
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Cite this page
ScholarGate. (2026, June 3). Eddy Covariance. ScholarGate. https://scholargate.app/meteorology/eddy-covariance