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Content: Motivation Observations Fetch Conditions Corrections Surface Energy Budget Advection

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

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Content: Motivation Observations Fetch Conditions Corrections Surface Energy Budget Advection

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  1. Regional scale flux observations at CabauwFred C. BosveldRoyal Netherlands Meteorological InstituteWith 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 EMS2011 September 12-16, Berlin 1

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

  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 EMS2011 September 12-16, Berlin 3

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

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

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

  7. Based on Kaimal (1972) surface layer spectra Extended by Schalkwijk et al (2010) 180 m 100 m 60 m 3 m 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 U = 5 m/s T=600 s EMS2011 September 12-16, Berlin 7

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

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

  10. Surface and 60 m sensible heat fluxes No constant flux layer Deriving fluxes from XLASat 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) CT2 from similarity functions with surface and local scaling, compared with CT2 derived directly from XLAS and from sonic at 60 m. EMS2011 September 12-16, Berlin 10

  11. Regional scale fluxes -> Advection (Diurnal variation) Sensible heat flux 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 EMS2011 September 12-16, Berlin 11

  12. 60-100m 100-180m CO2 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 EMS2011 September 12-16, Berlin 12

  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. EMS2011 September 12-16, Berlin 13

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