HR: 09:00h
AN: B21D-05    [Abstracts]
TI: A New Methodology For Estimating CO2 Advective Fluxes In Complex Terrain
AU: Montagnani, L
EM: leonar@inwind.it
AF: Autonomous Province of Bolzano, APB, Forest Service, via Brennero, 6, Bolzano, 39100, Italy
AU: Montagnani, L
EM: leonar@inwind.it
AF: Autonomous Province of Bolzano, APB, Agency for Environment, via Amba-Alagi, 5, Bolzano, 39100, Italy
AU: * Manca, G
EM: giovanni.manca@jrc.it
AF: Institute for Environment and Sustainability - Climate Change Unit, Joint Research Centre, European Commission, via Enrico Fermi, 1, Ispra, 21020, Italy
AU: Canepa, E
EM: elisa.canepa@fisica.unige.it
AF: CNR-INFM-CNISM - Department of Physics - University of Genova, Via Dodecaneso, 33, Genova, 16146, Italy
AU: Georgieva, E
EM: georgieva@fisica.unige.it
AF: Institute of Geophysics, Bulgarian Academy of Sciences, Acad G.Bonchev str. bl. 3, Sofia, 1113, Bulgaria
AU: Kerschbaumer, G
EM: Guenther.Kerschbaumer@provinz.bz.it
AF: Autonomous Province of Bolzano, APB, Agency for Environment, via Amba-Alagi, 5, Bolzano, 39100, Italy
AU: Minerbi, S
EM: stefano.minerbi@provinz.bz.it
AF: Autonomous Province of Bolzano, APB, Forest Service, via Brennero, 6, Bolzano, 39100, Italy
AU: Seufert, G
EM: guenther.seufert@jrc.it
AF: Institute for Environment and Sustainability - Climate Change Unit, Joint Research Centre, European Commission, via Enrico Fermi, 1, Ispra, 21020, Italy
AB: A key problem in using the eddy correlation (EC) technique for estimating the carbon dioxide Net Ecosystem Exchange (NEE) of terrestrial ecosystems is the potential bias caused by advective fluxes of CO2. Advective fluxes are often not considered since they are difficult to identify and to quantify, especially in complex mountainous terrain with highly variable wind patterns and drainage flows. We propose a methodology to estimate these fluxes based on a full 3-Dimensional (3D) approach applied to the topographically complex alpine forest site of Renon (1736 m a.s.l.). This is an aerodynamic method based on the computation of advective fluxes across the aerial faces of a control volume including the plant ecosystem. Data used for the computation of CO2 advective fluxes were collected during an extensive field campaign performed in 2005 in the framework of CarboEurope-IP research project. Vertical profiles of wind, air temperature and CO2 concentration have been measured at five towers and a spatial interpolation was performed in order to get 3D fields of such variables. The frame of reference used was orthogonal and the vertical direction was parallel to the gravity. Each anemometer was aligned in this frame of reference and no rotations were applied to the wind velocity components. The analysis of the 3D fields of wind velocity, CO2 mixing ratio and air density highlighted the spatial heterogeneity of CO2 source/sink strength and the strong de-coupling between air flow below and above the canopy during stable nights. The total CO2 advection calculated using the proposed methodology exhibited prevailing positive values during the night-time period. Advective fluxes estimated during windy nights were of the same magnitude and sign of vertical turbulent flux measured above canopy by the EC technique. This observation suggests that the friction velocity correction routinely applied to night-time periods may not be efficient at the Renon site. During light windy nights high positive values of advective fluxes were observed, while EC fluxes were close to zero. Daytime advection showed prevailing negative values. The magnitude of daytime advection was lower than the magnitude of night-time advection, and they tend to partially cancel out each other because of the opposite signs. Ecosystem respiration estimated by a chamber-based method was in good agreement with night-time NEE corrected for storage and total advection. By taking into account day and night advection the carbon uptake at Renon was reduced more than 50%, and this corrected value was in good agreement with biometric estimation of Net Ecosystem Productivity (NEP).
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 4806 Carbon cycling (0428)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting