1. EMS2011 September 12-16, Berlin 1 Regional scale flux observations at Cabauw Fred C. Bosveld Royal Netherlands Meteorological Institute With contributions of Miranda Braam, Kasper Gerritsen, Claudia Brauwer (Wageningen University) and Jerome Schalkwijk (Delft University) Content: Motivation Observations Fetch Conditions Corrections Surface Energy Budget Advection Conclusions

2. EMS2011 September 12-16, Berlin 2 http://www.cesar-observatory.nl http://www.cesar-database.nl Consortium van 8 instituten:

3. EMS2011 September 12-16, Berlin 3 Regional scale fluxes -> Motivation Surface fluxes at the scale of atmospheric model gridcel Surface fluxes at the scale of satellite pixel Surface Energy budget closure studies Evaluation of advection in models Cabauw serves as reference case since it is relatively homogeneous and very flat

4. EMS2011 September 12-16, Berlin 4 180 m 100 m 60 m 3 m Flux levels Extra LArge Scintillometer (XLAS) over a 10 km path at 60 m height Regional scale fluxes -> Observation Gill R3 sonic anemo/thermometer Licor 7500 H2O/CO2 sensor Cabauw 213 m meteorologival tower T,q, CO2 fluxes and concentrations Water budget of the polder

5. EMS2011 September 12-16, Berlin 5 Regional scale fluxes -> Fetch conditions 100m 60m 3m 180m Water Budget XLAS 10 km Tower 2 km

6. EMS2011 September 12-16, Berlin 6 - Mast interference N Sonic ESonic B Regional scale fluxes -> Corrections

7. EMS2011 September 12-16, Berlin 7 Regional scale fluxes -> Corrections - Standard corrections for eddy correlation technique Density, Flow distortion, sensor seperation -High accuracy needed Calibration issues - Low frequency flux contribution Extention of surface layer relations 180 m 100 m 60 m 3 m U = 5 m/s T=600 s Based on Kaimal (1972) surface layer spectra Extended by Schalkwijk et al (2010)

8. EMS2011 September 12-16, Berlin 8 Regional scale fluxes -> Surface fluxes Surface flux Local flux Storage flux Advective flux

9. EMS2011 September 12-16, Berlin 9 Regional scale fluxes -> Surface energy budget Mean diurnal variation of 8 comparable days Surface total heat flux (THF=H+LE) estimated from different heights. Available Energy (Qav=Qnet-G) Imbalance is independent of height of flux observation.

10. EMS2011 September 12-16, Berlin 10 Deriving fluxes from XLAS at 60 m height and 10 km path No constant flux layer in the morning ? Does CT2 at 60 m scales with: Surface sensible heat flux (s) Local sensible heat flux at 60 m (l) Braam et al. (subm. BLM) Surface and 60 m sensible heat fluxes No constant flux layer C T 2 from similarity functions with surface and local scaling, compared with C T 2 derived directly from XLAS and from sonic at 60 m.

11. EMS2011 September 12-16, Berlin 11 Regional scale fluxes -> Advection (Diurnal variation) April-June 2008 Difference in surface flux between 60 – 100 m and 100 – 180 m Some indication of higher local latent heat flux. CO2 Latent heat flux Sensible heat flux

12. EMS2011 September 12-16, Berlin 12 Regional scale fluxes -> Advection (Wind direction) Difference in surface flux between 60 – 100 m and 100 – 180 m April-June 2008 daytime 30 min values and wind direction class mean values Some signature visible Sensible heat flux Latent heat flux CO2 60-100m100-180m

13. EMS2011 September 12-16, Berlin 13 Conclusions The Cabauw 213 m meteorological tower gives a unique opportunity to perform tower based regional scale flux observations. The site is flat and rather homogeneous. Special care for low frequency flux loss correction Surface energy imbalance independent of measuring height Scaling of scintillometer at 60 m (outside constant flux layer) investigated Slightly significant signals in advection found both in time of day and in wind direction.