On the Closure of the Surface Energy Balance in Highly Complex Terrain

1. On the Closure of the Surface Energy Balance in Highly Complex Terrain Mathias W. Rotach, Pierluigi Calanca, Andreas Weigel, Marco Andretta Swiss Federal Institute of TechnologyInstitute for Atmospheric and Climate Science

2. Layout • Surface energy balance • Data: MAP -Riviera project • Energy balance for a layer • Implications for modeling

3. MAP-Riviera Valley Floor Slope site Average 15 fair-weather days

4. Surface Energy balance NR-G=Ho+LvEo Ho LvEo NR G

5. Surface Energy balance NR-G=Ho+LvEo • horizontally homogeneous surfaces --> constant turbulent fluxes --> no advection-->closure! [even @ z≠0...]

6. Surface Energy balance NR-G=Ho+LvEo • horizontally homogeneous surfaces --> constant turbulent fluxes --> no advection-->closure! [even @ z≠0...]--> non-closure: measurement error turbulence time scales

7. Surface Energy balance NR-G=Ho+LvEo • horizontally homogeneous surfaces --> constant turbulent fluxes --> no advection-->closure! [even @ z≠0...]--> non-closure: measurement error turbulence time scalescomplex terrain...

8. MAP Riviera project Biasca Riviera Bellinzona Lago Maggiore

9. MAP Riviera project

10. MAP Riviera Project

11. MAP-Riviera: Bosco di Sotto turbulence @ 4 / 16 / 28 m Full radiation comp, precip, profiles,sfc. hydrology Local slope app. 0.5° Local surface: corn, grass

12. Near-Surface Energy Balance H(zr) LvE(zr) NR zr Ho LvEo G

13. Near-Surface Energy Balance NR-G=Storage+horiz.Adv +vert.Adv Hr LvEr NR z=zr Ho LvEo G

14. Corrections • Sensible Heat flux:--> frequency response (Moore 1986) • --> humidity cross-correlation (Schotanus et al. 1983) • Latent heat flux: --> frequency response (Moore 1986) --> Oxygen (Dijk et al. 2003) • --> WPL-correction (Webb et al. 1980)

15. Horizontal Advection Comprovasco Riviera Magadino

16. Vertical Advection zr Mean vertical wind: from planar fit

17. Results...

18. Energy balance terms NR New sum H+LE+G LE H G Average 7 clear sky days

19. Contributing terms Sum new terms Vertical advection Sum corrections Storage soil Storage air / horiz. advection Average 7 clear sky days

20. Vertical advection Proprtional Difference in Q, q....

21. Vertical advection Proprtional mean vertical wind

22. Energy balance terms NR New sum H+LE+G LE H G Average 7 clear sky days

23. Conclusions • Sfc. energy balance in really complex terrain: good to detect processes • Corrections to turbulent fluxes important • Soil storage term important • Vertical advection!--> largest--> most uncertain!

24. Outlook • If indeed vertical advection is substantial....--> too large a fraction of NR --> H, LE--> cold / dry bias

25. RAMS simulations - August 25 1999 12.08 UTC 9.15 UTC observations model De Wekker et al. 2003

26. Salt Lake Valley - VTMX Different models: RAMSMM5ETA IOP‘s 6,7,10 Zhong and Fast 2002

27. Outlook • If indeed vertical advection is substantial....--> too large a fraction of NR --> H, LE--> cold / dry bias • How to parameterize in numerical models?

28. Comparisons of observed and simulated sensible heat fluxes

29. Hydrological modeling – valley floor ET und LE [mm/h] ET und LE [W/m2] Soil moisture (.5m) Precipitation [mm/h] Sept 1 1999 Sept 21 1999

30. Hydrological modeling – valley floor Observation(Bowen Ratio) Model (Penman- Monteith) ET und LE [W/m2] Eddy Correlation time

31. Closed energy balance • Bowen ratio method: --> if and

32. Planar fit Plot w as a function of (u,v)....

33. Planar fit on a slope

34. Planar fit vs. Double rotation Common plane vs. local planes (<u‘w‘>PFC -<u‘w‘>DR)/<u‘w‘>DR (<u‘w‘>PFC -<u‘w‘>PF)/<u‘w‘>PFC Andretta et al. (2002)

35. Energy Balance closure Data from a ‚flux site‘ in Manaus, Brazil Finnigan et al. 2003