1. Characteristics of horizontal and vertical fluxes of CO 2 during the ADVEX Experiment at the Wetzstein site, in Thuringia, Germany Marcelo Zeri 1, Corinna Rebmann 1, W. Kutsch 1, C. Feigenwinter 2, ADVEX teams (1) Max Planck Institute for Biogeochemistry; (2) University of Basel, Institute of Meteorology, Climatology and Remote Sensing, Basel, Switzerland

2. Overview Introduction Site characteristics Advection versus micrometeorology Indirect measures of advection periods Conclusions

3. The Advection Experiment Performed in three European sites (Renon, Italy; Wetzstein, Germany; Norunda, Sweden) Measurements performed with multiple towers Horizontal and vertical advection of CO2 calculated to a volume First results summarized in Feigenwinter et al. (Agr. For. Met, accepted)

4. The Wetzstein site

5. Spruce ecosystem Located at 785 m a.s.l. Average temperature of ~ 6 C; annual precipitation of 990 mm Unexplained high nighttime fluxes of CO 2 One of the sites of the CarboEurope-IP Advection Experiment

6. Advection versus micrometeorology Inspection of the time series of horizontal and vertical advection (HA and VA) Relation with variables as wind speed and direction, stratification, and CO 2 -flux Three patterns identified:  No advection  Both terms important (|HA|>|VA|)  HA only

7. First case, May 2006 Advective fluxes provided by Christian Feigenwinter

8. Second case, May-June, 2006 Advective fluxes provided by Christian Feigenwinter

9. Identifying periods with advection

12. Conclusions The evolution of the advection terms exemplify the non- stationary nature of these terms. Site specific characteristics of the topography, and local synoptic conditions may influence their evolution in time. As the advection terms are intermittent, an average for a continuous period may not represent its real day-to-day contribution. Periods with horizontal advection can be identified by, for example, the maximum in the vertical profile of wind speed below the canopy or by the positive correlation w’u’ at the trunk space. Periods characterized by advection should be removed from the determination of annual sums of CO2-flux, as commonly done with nights with low friction velocity.

13. Acknowledgements The authors gratefully acknowledge the collection of data by the field crew from the Max Planck Institute for Biogeochemistry and from the ADVEX Experiment in 2006. Reference Feigenwinter, C. et al., The ADVEX advection field campaigns: Comparison of mean horizontal and vertical non turbulent advective fluxes at three CarboEurope forest sites. Agricultural and Forest Meteorology, (accepted).