Assessing decoupling of above and below canopy air masses at a Norway spruce stand in mountainous terrain

0511530 - ÚVGZ 2020 AT eng A - Abstrakt
Jocher, Georg - Fischer, Milan - Pavelka, Marian - Šigut, Ladislav - Sedlák, Pavel
Assessing decoupling of above and below canopy air masses at a Norway spruce stand in mountainous terrain.
Geophysical Research Abstracts. Vol. 21. European geoscience union, 2019.
[EGU General Assembly Conference 2019. 07.04.2019-12.04.2019, Vídeň]
Institucionální podpora: RVO:86652079
Klíčová slova: advection * eddy covariance * evergreen needleleaf forest * flux filtering * net ecosystem co2 exchange
Obor OECD: Forestry

Above canopy eddy covariance (EC) derived forest carbon fluxes might be biased due to decoupling and insufficient mixing between above and below canopy air masses and consequently missing soil respiration components in the above canopy derived data. The most common way to address insufficient mixing across the canopy is to filter the above canopy derived fluxes at a certain u*-threshold. However, at some sites like e.g. at the current study site Bílý Kríž (49°300N, 18°320E; 800–900 m a.s.l.) located in the Moravian-Silesian Beskydy Mountains, the Czech Republic, it is not possible to identify a u*-threshold due to the complexity of the surrounding terrain. The Bílý Kríž experimental forest is a ~ 40 years old Norway spruce (Picea abies /L./, Karst) monoculture with a leaf area index of ~ 9 m2 m-2 in 2016. Recently, a below-canopy EC system was installed at the study site to support the interpretation of the above canopy derived EC data. Amongst others, such a below-canopy system provides readings of the standard deviation of vertical wind (σw). The correlation of σw between above and below canopy EC measurements remarkably differs for the cases of decoupling and the cases of full coupling between below and above canopy air masses. With this study we aim to assess decoupling with a set of two-level filtering approaches based on 1 year (August 2017 – July 2018) of vertical wind measurements above and below the canopy: i) σw (described above), ii) telegraphic approximation (w) which identifies periods where the vertical wind above and below the canopy is directed in the same direction and considers these periods as coupled, iii) cross correlation maximum (w) which is used as measure for maximum of below-above canopy coupling. Finally, recommendations shall be derived how to treat carbon exchange EC data at forested sites in complex terrain in the most proper way to minimize potential biasing effects by decoupling on the above canopy derived carbon fluxes.
Trvalý link: http://hdl.handle.net/11104/0301774