Consequences of Incomplete Surface Energy Balance Closure for CO_2 Fluxes from Open-Path CO_2/H_2O Infrared Gas Analysers

Abstract

We present an approach for assessing the impact of systematic biases in measured energy fluxes on CO_2 flux estimates obtained from open-path eddy-covariance systems. In our analysis, we present equations to analyse the propagation of errors through the Webb, Pearman, and Leuning (WPL) algorithm [Quart. J. Roy. Meteorol. Soc. 106, 85–100, 1980] that is widely used to account for density fluctuations on CO_2 flux measurements. Our results suggest that incomplete energy balance closure does not necessarily lead to an underestimation of CO_2 fluxes despite the existence of surface energy imbalance; either an overestimation or underestimation of CO_2 fluxes is possible depending on local atmospheric conditions and measurement errors in the sensible heat, latent heat, and CO_2 fluxes. We use open-path eddy-covariance fluxes measured over a black spruce forest in interior Alaska to explore several energy imbalance scenarios and their consequences for CO_2 fluxes.

Additional details