Stability dependence of the relaxed eddy accumulation coefficient for various scalar quantities

Abstract

[1] The coefficient b of the relaxed eddy accumulation (REA) technique was investigated by simulation studies using extensive high-resolution eddy correlation data sets of three different scalar quantities: the air temperature and the concentrations of CO 2 and H 2 O. Measurements were performed in June -July 1995 over a senescent cereal field in the Rhineland-Palatinate region of southwestern Germany. The wide range of stability conditions during the experiment made it possible to describe the coefficient b as a function of the dimensionless stability parameter z/L within the framework of the Monin-Obukhov similarity theory. In good agreement with previous publications, a constant value of about 0.56 was obtained for unstable and near-neutral conditions if no dead band applied. For stable conditions, however, a significant increase with stability was observed which could be well described by a logarithmic functional relationship between b and z/L. By additional dead-band simulation studies the relationship was extended to variable dead-band widths. The observed dependency on z/L is interpreted in relation to the bivariate joint frequency distribution of the vertical wind speed and the scalar quantity.

Measurements of hydrocarbon emissions from a boreal fen using the REA technique

“…This increases the concentration difference between the two reservoirs thus decreasing the precision requirement for the chemical analysis. The dynamic deadband also forces the parameter β to become practically constant (β=0.41) and independent of turbulence intensity or atmospheric stability (Christensen et al, 2000;Ammann and Meixner, 2002;Grönholm et al, 2006 1 ). Variations in the value of the parameter β cause large uncertainty to a single measurement point.…”

A disjunct eddy accumulation system for the measurement of BVOC fluxes: instrument characterizations and field deployment

“…The use and impact of this dead-band threshold in REA measurements have been well documented (e.g., Oncley et al, 1993;Bowling et al, 1999;Ammann and Meixner, 2002;Ren et al, 2011), but the application has not been applied to the few DEA measurements so far reported (Rinne et al, 2000(Rinne et al, , 2002Turnipseed et al, 2009). Since our sampler therefore differs from the methodologies described to date, we must then assess the impact on the calculated fluxes.…”

“…In REA instruments, this is compensated for by adjusting a dimensionless, empirical coefficient β used to calculate REA flux. Usually, this is achieved by conditionally sampling at 10 Hz wind/temperature data to derive the β coefficient with the same threshold used as when sampling/accumulating at valve speeds < 10 Hz (e.g., Bowling et al, 1999;Ammann and Meixner, 2002). In true DEA sampling, no such empirical correction coefficients are used in the calculation of DEA flux, but, by using a dead-band approach for data all recorded using our sampler, a smaller factor is needed.…”

A whole-air relaxed eddy accumulation measurement system for sampling vertical vapour exchange of elemental mercury

“…In that case, if w 5 0 À w 0 BwBw 5 0 þ w, neither valve was activated. Accounts providing information about the effect and benefits of using a deadband in REA can be found elsewhere (Ammann and Meixner, 2002;Gro¨nholm et al, 2008). The relaxation coefficient b w 0 s for a deadband application is in relation to that of a zero-deadband (b 0 s ) according to Businger and Oncley (1990) that at the moment is not activated for sampling.…”