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High‐quality eddy‐covariance CO 2 budgets under cold climate conditions
Author(s) -
Kittler Fanny,
Eugster Werner,
Foken Thomas,
Heimann Martin,
Kolle Olaf,
Göckede Mathias
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2017jg003830
Subject(s) - eddy covariance , gas analyzer , anemometer , environmental science , sensible heat , atmospheric sciences , heat flux , flux (metallurgy) , spectrum analyzer , meteorology , turbulence , mechanics , chemistry , physics , heat transfer , ecosystem , optics , ecology , organic chemistry , environmental chemistry , biology
This study aimed at quantifying potential negative effects of instrument heating to improve eddy‐covariance flux data quality in cold environments. Our overarching objective was to minimize heating‐related bias in annual CO 2 budgets from an Arctic permafrost system. We used continuous eddy‐covariance measurements covering three full years within an Arctic permafrost ecosystem with parallel sonic anemometers operation with activated heating and without heating as well as parallel operation of open‐ and closed‐path gas analyzers, the latter serving as a reference. Our results demonstrate that the sonic anemometer heating has a direct effect on temperature measurements while the turbulent wind field is not affected. As a consequence, fluxes of sensible heat are increased by an average 5 W m −2 with activated heating, while no direct effect on other scalar fluxes was observed. However, the biased measurements in sensible heat fluxes can have an indirect effect on the CO 2 fluxes in case they are used as input for a density‐flux WPL correction of an open‐path gas analyzer. Evaluating the self‐heating effect of the open‐path gas analyzer by comparing CO 2 flux measurements between open‐ and closed‐path gas analyzers, we found systematically higher CO 2 uptake recorded with the open‐path sensor, leading to a cumulative annual offset of 96 gC m −2 , which was not only the result of the cold winter season but also due to substantial self‐heating effects during summer. With an inclined sensor mounting, only a fraction of the self‐heating correction for vertically mounted instruments is required.