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Comparison of horizontal and vertical advective CO2 fluxes at three forest sites

Author:
  • Christian Feigenwinter
  • Christian Bernhofer
  • Uwe Eichelmann
  • Bernard Heinesch
  • Martin Hertel
  • Dalibor Janous
  • Olaf Kolle
  • Fredrik Lagergren
  • Anders Lindroth
  • Stefano Minerbi
  • Uta Moderow
  • Meelis Mölder
  • Leonardo Montagnani
  • Ronald Queck
  • Corinna Rebmann
  • Patrik Vestin
  • Michel Yernaux
  • Marcelo Zeri
  • Waldemar Ziegler
  • Marc Aubinet
Publishing year: 2008
Language: English
Pages: 12-24
Publication/Series: Agricultural and Forest Meteorology
Volume: 148
Issue: 1
Document type: Journal article
Publisher: Elsevier

Abstract english

Extensive field measurements have been performed at three CarboEurope-Integrated Project forest sites with different topography (Renon/Ritten, Italian Alps, Italy; Wetzstein, Thuringia, Germany; Norunda, Uppland, Sweden) to evaluate the relevant terms of the carbon balance by measuring CO2 concentrations [CO2] and the wind field in a 3D multi-tower cube setup. The same experimental setup (geometry and instrumentation) and the same methodology were applied to all the three experiments. It is shown that all sites are affected by advection in different ways and strengths. Everywhere, vertical advection (F-VA) occurred only at night. During the day, F-VA disappeared because of turbulent mixing, leading to a uniform vertical profile of [CO2]. Mean F-VA was nearly zero at the hilly site (wetzstein) and at the flat site (Norunda). However, large, momentary positive or negative contributions occurred at the flat site, whereas vertical non-turbulent fluxes were generally very small at the hilly site. At the slope site (Renon), F-VA was always positive at night because of the permanently negative mean vertical wind component resulting from downslope winds. Horizontal advection also occurred mainly at night. It was positive at the slope site and negative at the flat site in the mean diurnal course. The size of the averaged non-turbulent advective fluxes was of the same order of magnitude as the turbulent flux measured by eddy-covariance technique, but the scatter was very high. This implies that it is not advisable to use directly measured quantities of the non-turbulent advective fluxes for the estimation of net ecosystem exchange (NEE) on e.g. an hourly basis. However, situations with and without advection were closely related to local or synoptic meteorological conditions. Thus, it is possible to separate advection affected NEE estimates from fluxes which are representative of the source term. However, the development of a robust correction scheme for advection requires a more detailed site-specific analysis of single events for the identification of the relevant processes. This paper presents mean characteristics of the advective CO2 fluxes in a first site-to-site comparison and evaluates the main problems for future research.

Keywords

  • Physical Geography
  • ADVEX
  • carbon balance
  • net ecosystem exchange
  • advection
  • forest ecosystems

Other

Published
  • ISSN: 1873-2240
E-mail: meelis [dot] molder [at] nateko [dot] lu [dot] se

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Department of Physical Geography and Ecosystem Science
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