Random and systematic CO2 flux sampling errors for tower measurements over forests in the convective boundary layer

The perturbation timescale-dependences of the CO2 flux and the random flux sampling error are evaluated from eddy-covariance tower observations in the mid-day convective boundary layer over mid-latitude conifer forests. The perturbation timescale is the timescale used in the standard Reynolds decomposition to define mean and perturbations quantities. The random error due to inadequate sampling of the turbulence is estimated using two different approaches (traditional and daily-differencing). A fixed record length of 3.6 h (dyadic timescale) is used for all results, where the record length is the timescale over which the products of perturbations are averaged (flux averaging timescale). Long multiple-hour records are required to evaluate the sampling errors.