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Charuchittipan, Doojdao ; Babel, Wolfgang ; Mauder, Matthias ; Leps, Jens-Peter ; Foken, Thomas:
Extension of the averaging time in eddy-covariance measurements and its effect on the energy balance closure.
In: Boundary-Layer Meteorology.
Bd. 152
(2014)
Heft 3
.
- S. 303-327.
ISSN 1573-1472
DOI: https://doi.org/10.1007/s10546-014-9922-6
Abstract
The modified ogive analysis and the block ensemble average were employed toinvestigate the impact of the averaging time extension on the energy balance closure oversix land-use types. The modified ogive analysis, which requires a steady-state condition, canextend the averaging time up to a few hours and suggests that an averaging time of 30 minis still overall sufficient for eddy-covariance measurements over low vegetation. The blockensemble average, which does not require a steady-state condition, can extend the averagingtime to several days.However, it can improve the energy balance closure for some sites duringspecific periods, when secondary circulations exist in the vicinity of the sensor. These nearsurfacesecondary circulations mainly transport sensible heat, and when near-ground warmair is transported upward, the sensible heat flux observed by the block ensemble averagewill increase at longer averaging times. These findings suggest an alternative energy balancecorrection for a ground-based eddy-covariance measurement, in which the attribution of theresidual depends on the ratio of sensible heat flux to the buoyancy flux. The fraction of the residual attributed to the sensible heat flux by this energy balance correction is larger than inthe energy balance correction that preserves the Bowen ratio.