High‐quality eddy‐covariance CO2 budgets under cold climate conditions. Issue 8 (19th August 2017)

• Record Type: Journal Article
• Authors: Kittler, Fanny; Eugster, Werner; Foken, Thomas; Heimann, Martin; Kolle, Olaf; Göckede, Mathias
• Is Part Of: Journal of geophysical research. Volume 122:Issue 8(2017)
• Page Start: 2064
• Page End: 2084
• Publication Date: 2017-08-19
• Subjects: Arctic -- eddy covariance -- open path -- closed path -- sonic anemometer -- heating; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2017JG003830
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: 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 CO2 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 CO2 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 CO2 flux measurements between open‐ and closed‐path gas analyzers, we found systematically higher CO2 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. Key Points: Self‐heating of the open‐path gas analyzer can lead to systematic offsets in CO2 flux budgets, causing an annual bias of about 100 gC m −2 Sonic anemometer heating directly affected temperature measurements but not the turbulent wind field Both instrument heating effects have to be considered to compute unbiased CO2 budgets in cold ecosystems