Advective effects on short term and long term Net Ecosystem Exchange

1. Advective effects on short term and long term Net Ecosystem Exchange C. Feigenwinter1, C. Bernhofer2, R. Vogt1 , T. Grünwald2, U. Eichelmann2, H. Prasse2, U. Postel2 1 University of Basel, Institute of meteorology, climatology and remote sensing 2 TU-Dresden, Institute of hydrology and meteorology

2. Overview Advective effects on short term and long term Net Ecosystem Exchange C. Feigenwinter1, C. Bernhofer2, R. Vogt1 , T. Grünwald2, U. Eichelmann2, H. Prasse2, U. Postel2 1 University of Basel, Institute of meteorology, climatology and remote sensing 2 TU-Dresden, Institute of hydrology and meteorology • Site overview • Results and conclusions MORE I • Experimental setup MORE II (More measurements in the ORE mountains) • Short theory and methodology • Results MORE II • effects of advective fluxes on NEE • Conclusions and outlook

3. Site overview Elevation Landuse Inclination Exposition Overview anchor station Tharandter Wald 50°58‘ N, 13°34‘ E 375 m a.s.l. Annual mean temp. 7.7° Annual mean precip. 819 mm

4. MORE I Results from MORE I (2001, DOY 263-283) (Feigenwinter et al., 2004, Boundary-Layer Meteorol., in press) -----EC + storage change  + advection terms difference: 0.18 g C m-2 d-1 (10 %)

5. MORE I Conclusions from MORE I • Methododical problems and deficits for evaluation of the advection terms (i.e. vertical profiles of wind velocity, CO2 concentrations and horizontal concentration gradients are strongly dependent on the experimental design) • Short duration of the MORE I experiment does not allow conclusions that are generally valid. Results have to be confirmed and/or adjusted by long term measurements. • Results published in: • Feigenwinter, C., Bernhofer, C. and Vogt, R. (2004): The influence of advection on the short term CO2 budget in and above a forest canopy, Boundary-Layer Meteorology, in press. • MORE II Long term study (growing season) Experimental setup essentially improved Optimised coordination between measurements (gradients, wind profile, sampling rates) Adaptation of the permanent measurements according to the task

6. Experimental setup: Situation Experimental setup situation MORE I : Sep/Oct 2001 height (trees)26 m (P2, P3) MORE II: Mai/Oct 2003 height (towers) 30 m (P1, P2, P3)

7. Experimental setup MORE II Experimental setup: Instrumentation

8. Experimental setup: Tower P1

9. Experimental setup: Tower P2

10. Experimental setup: Tower P3

11. Theory and methodology Experimental evaluation of CO2 exchange in a forest ecosystem I source/sink of c II storage change III turbulent flux(EUROFLUX, Aubinet et al., 2000; FLUXNET, Agr. For. Met. Vol. 113, 2002) IV vertical advection(Lee, 1998; Baldocchi, 2000) V horizontal advection(Aubinet et al., 2003, Staebler and Fitz-jarrald, 2004; Feigenwinter et al., 2004)

12. Theory and methodology Estimation of the mean vertical wind component: sinusoidal fit over a sufficiently long period(Lee, 1998; Baldocchi et al., 2000; Paw U et al. (2000))or „planar fit“(Wilczak et al., 2001) Theory und methodology non turbulent advection terms vertical advection

13. Theory and methodology Theory und methodology non turbulent advection terms vertical advection ● tower P1 (30 m) ● tower P2 (30 m) ● tower P3 (30 m) ● main tower (anchor station) Estimation of the mean CO2 concentration in the volume below the reference level: and log-square fit of the concentration profiles

14. Theory and methodology Theory und methodology non turbulent advection terms horizontal advection __ sonics__cup anemometer ___ measured gradient

15. Results MORE II positive during nighttime with large scatterzero during daytime Results non turbulent advection terms vertical advection

16. Results MORE II Theory und methodology non turbulent advection terms horizontal advection • Flow conditions during MORE II (DOY 155-285) • mainly from SW – W – NW • - no distinct drainage flow at night

17. Results MORE II Theory und methodology non turbulent advection terms horizontal advection • Distribution of horizontal concentration gradients during MORE II (DOY 155-285) • large in the lower trunk space at night • - main direction NE – E - SE

18. Results MORE II Theory und methodology non turbulent advection terms horizontal advection • Horizontal advection MORE II (DOY 155-285) • large in the lower trunk space at night, large scatter • positive (source term)! • - zero during daytime Fluxes for a layer thickness of 1 m at the resp. height  0.5 m  2.0 m  8.0 m  20.0 m  30.0 m

19. Results MORE II Theory und methodology non turbulent advection terms horizontal advection • Horizontal advection MORE II (DOY 155-285) • large in the lower trunk space at night • positive (source term)! • - small during daytime

20. Conclusions and outlook Conclusions and outlook • Vertical and horizontal advection are in the same order of magnitude as the turbulent EC-flux of CO2 • The large scatter of the mean advection terms is the result of a large day to day variability • Including the advection terms into the NEE equation significantly increases the nightly CO2 source and thus reduces the Carbon sink of the forest • There are still many methododical problems and only a few studies for comparison. The presented results may therefore only be characterisic for the specific site