Eddy covariance

LewickiJ.L., HilleyG.E., et al. Eddy covariance observations of surface leakage during shallow subsurface C02 releases. 2009 Journal of Geophysics Reservoir 114. 

One of the most accurate methods for determining gas exchange in this region of the boundary layer is called the eddy covariance or eddy correlation method. To apply the method, scientists measure the individual upward and downward components of the turbulent exchange and calculate a net difference (48,49). Stated mathematically, the relationship becomes ... 

Fast Response CO Sensor. The sensor requirements for eddy covariance measurements are extreme. To be used within a few meters of a plant canopy, the sensor must have a frequency response in excess of 20 Hz. Additionally, because the large mean density of CO2 in the atmosphere (about 560 mg m-3) and the deviations around the mean associated with turbulent transfer are small (>10 mg m-3), the sensor must have a signal to noise ratio in excess of 3500 1. The sensor must maintain these specifications for long durations, while mounted on a tower above the canopy, where it is exposed to constant changes in temperature, solar irradiation, and background gas concentrations. The instrument must unobtrusively sense the natural turbulant fluctuations of the atmosphere. To effectively accomplish this it must be small and streamlined. 

Pattey, E., Strachan, I.B., Desjardins, R.L., and Massheder, J. 2002. Measuring nighttime COz flux over terrestrial ecosystems using eddy covariance and nocturnal boundary layer methods. Agric. Forest Meteorol. 113 145-158. 

Miranda, A. C., H. S. Miranda, J. Lloyd, J. Grace, R. J. Francey, J. A. McIntyre, P. Riggan, R. Lockwood, and J. Brass. 1996b. Fluxes of carbon, water and energy over Brazilian cerrado An analysis of eddy covariation and stable isotope. Plant Cell and Environment. 

Lowlands. Sites in areas of discontinuous permafrost as well as other areas susceptible to permafrost melting should be part of the network. Static chamber flux measurements are legendary as labor-intensive, and they should be replaced where possible with automated chambers and supplemented with continuous eddy flux measurements (Hargreaves et al., 2001). Development of a held-portable, rapid-response CH4 sensor suitable for continuous eddy covariance measurements should be a high priority. 

Hargreaves K. J., Fowler D., Pircairn C. E. R., and Aurela M. (2001) Annual methane emission from Einnish mires estimated from eddy covariance campaign measurements. Theor. Appl. Climatol. 70, 203-213. 

Buzorius G., RannikU., Makela J. M., Vesala T., and Kuhnala M. (1998) Vertical aerosol particle fluxes measured by eddy covariance technique using condensational particle counter. J. Aerosol Sci. 29, 157-171. 

As discussed below, knowledge of NEE and S Cnee are prerequisites for the partitioning of NEE into its photosynthetic and respiratory components. Preliminary results of using this approach gave close agreement with surface-based, eddy covariance and isotopic measurements. 

The dynamics of canopy-scale net fluxes of water and CO2 exchanged between vegetation and the atmosphere are routinely measured today with micrometeorological methods (e.g., with eddy covariance www.daac.ornl.gov/FLUXNET/ fluxnet.html). Combining these methods with isotopic measurements allows to partition a net flux into its gross flux components. The approach here is similar to that used on the global scale to... 

Miranda A. C., Miranda H. S., Lloyd J., Grace J., Francey R. J., McIntyre J. A., Meir P., Riggan P., Lockwood R., and Brass J. (1997) Fluxes of carbon, water, and energy over Brazilian Cerrado an analysis using eddy covariance and stable isotopes. Plant Cell Environ. 20(3), 315-328. 

Jacobs C., Kjeld J. F., Nightingale P., Upstill-Goddard R., Larsen S., and Cost W. (2002) Possible errors inC02air-sea transfer velocity from deliberate tracer releases and eddy covariance measurements due to near-surface concentration gradients. J. Geophys. Res. 107 article no. 3128. 

Figure 34 Steady-state SOM mean residence times derived from eddy covariance data plotted against MAT. Bold solid curve is Lloyd and Taylor fit bold dashed curve is the 2io best fit and light dashed curve represents a linear regression wit, the common log of turnover time (source Sanderman et aL, 2003).

Janssens I. A., Kowalski A. S., and Ceulemans R. (2001) Forest floor CO2 fluxes estimated by eddy covariance and chamber-based model. Agri. Forest Meteorol. 106(1), 61—69. 

Sanderman J., Amundson R., and Baldocchi D. D. (2003) Application of eddy covariance measurements to the temperature dependence of soil organic matter mean residence times. Global Biogeochem. Cycles, 17(2), 1061. 

Hammerle, A. Haslwanter, A., Schmitt, M., Bahn, M., Cernusca, A., Wohlfahrt, G. (2006) Eddy covariance measurements of carbon dioxide, latent and sensible energy fluxes above a meadow on a mountain slope, Boundary-Layer Meteorol. (Submitted)... 

Figure 8. PTR-MS can be used for eddy covariance measurements of VOC fluxes. A fast-response PTR-MS instrument, described in the text, was used to measure the concentration of methanol at a height of 450 cm above ground in a hay field following mowing the corresponding vertical wind speed at this height was also measured. Data redrawn from Ref. [45].

The accumulation of carbon in the organic layer after fire points at a basic problem of the simplified flux scheme of Schulze and Heimann (1998), namely, that intermediate pools exist at each level with different mean residence time, and depending on the level of spatial integration these pools may or may not average out. The problem is illustrated in Figure 7, where an inventory-process type approach (in contrast to eddy covariance flux measurements) was chosen to calculate the carbon sink capacity of European forest ecosystems. If NPP was plotted against C-mineralization, then NPP minus C-mineral-ization would represent NEP at the plot scale (Schulze et al.,... 

Flux-resolving, fluctuation-based methods In these methods the vertical turbulent eddy flux F is measured as pw c, where overbars and primes denote time means and fluctuations, respectively, and w is the vertical velocity component. They include eddy-covariance and eddy-accumulation methods for measuring fluxes from towers and aircraft. They are not normally regarded as atmospheric inverse methods, since that term usually refers to methods which relate a mean concentration field to a source density or surface flux distribution. 

Grace, J., Malhi, Y., Lloyd, J., McIntyre, L, Miranda, A. C., Meir, P, and Miranda, II. S. (1996). The it.se of eddy-covariance to infer the net carbon-dioxide uptake of Brazilian rain forest. Global Change Biol. 2, 209-218. 

Boreal zone forest stands are also part of a patchy landscape at least in terms of tree age, size, and density, which determine stand structure. More commonly, though, the stands of trees are interspersed with herbaceous and shrubby vegetation and wetlands. On average, P is found to be 0.5 mm day less than ( = 2.3 mm day ) for forests in summer. Rainfall interception has been included in this comparison because E comprised wet and dry canopy evaporation rates except for the Yakutsk study by Kelliher et al. (1997). The difference between rainfall and evaporation rates is up to 2 mm day for the two oldest studies. These studies also report by far the highest evaporation rates. These E measurements were made using the Bowen ratio technique, which is notoriously difficult to employ over forests because of the small gradients in temperature and humidity there. Except for Lalleur (1992), who also used this technique, the other measurements were made directly by eddy covariance. 

I Measured by the Eddy Covariance Technique above Each... 

Amiro, B. D., and Wuschke, E. E. (1987). Evapotran.spiration from a boreal forest drainage basin using an energy balance/eddy covariance tech-niciue. Bonnilory Layer Meteorol. 38, 125-139. 

In view of the difficulties in determining gas transfer coefficients accurately, direct methods for CO2 flux measurements aboard the ship are desirable. Sea-air CO2 flux was measured directly by means of the shipboard eddy-covariance method over the North Atlantic Ocean by Wanninkhof and McGillis in 1999. The net flux of CO2 across the sea surface was determined by a covariance analysis of the tri-axial motion of air with CO2 concentrations in the moving air measured in short time intervals ( ms) as a ship moved over the ocean. The results obtained over awind speed range of 2-13.5 m s are consistent with eqn [3] within about +20%. If the data obtainedin wind speeds up to 15 m s are taken into consideration, they indicate that the gas transfer piston velocity tends to increase as a cubeof wind speed. However, because of a large scatter ( + 35%) ofthe flux values at high wind speeds, further work is needed to confirm the cubic dependence. 

Li S, Kang S, Li F, Zhang L. Evapotranspiration and crop coefficient of spring maize with plastic mulch using eddy covariance in northwest China. Agric Water Manag 2008 95 (11) 1214-1222. 

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