EUCLIPSE Toulouse meeting April 2012

1. EUCLIPSE Toulouse meeting April 2012 Process-level evaluation at selected grid-points: Constraining a system of interacting parameterizations through multiple parameter evaluation at Cabauw Roel Neggers

2. Process-level evaluation We have built good experience at (idealized) single-case level (e.g. GCSS), and can demonstrate successes in model improvement. However, possible shortcomings: * Cases might not represent actual climate; parameterizations might get tuned to rare situations * Cases might not represent those situations that are most troublesome in GCMs; * The use of relevant observational data has been somewhat limited. These arguments motivate a move towards more comprehensive, statistically significant approach in model evaluation, in combination with a more efficient use of observational datasets.

3. The “testbed” idea Neggers et al, BAMS, in press, 2012 1) SCM and GCM evaluation for long periods of time at permanent meteorological sites (e.g. ARM, CloudNet) Emphasis: fast physics (boundary-layer, soil) 2) Use a multiple-parameter approach in the evaluation (“CloudNet+”) Constrain the system of interacting parameterizations at multiple points with key measurements Goals: * Try and identify compensating errors in interaction between low clouds & radiative transfer (e.g. too bright – too few) * Trace their impact through the coupled BL – soil system (heat & moisture budgets)

4. Short example The motivation: problems with a new BL scheme in IFS Too little cloud cover at noon

5. Associated 2m T warm bias over land

6. Hypothesis SW 1. less PBL clouds 4. low level warming 2. larger SW down 3. larger H Can long-term SCM evaluation at Cabauw provide some insight?

7. Long-term SCM evaluation at Cabauw (2007-2010) Obs vs Model scatterplots of monthly means RACMO SCM: Control (red) and new (blue) scheme RACMO 3D in forecast mode (grey)

8. 8-point check Expanding to multiple independently-measured parameters that reflect the impact mechanism as illustrated before

9. Model performance – Taylor diagram Reproduction of observed pattern in variation of monthly-mean

10. Correlation between model differences

11. Tracing impacts Following degrading correlations in coupled BL – soil system

12. Zooming in

13. Identifying regimes Cabauw cloud-scenes on 8 days with biggest model difference

14. Conditional sampling Make a list of shallow cu days Criterion: positive surface buoyancy flux LCL below BL top Total cloud cover < 50%

15. control new Evaluation against LES zbase One month of DALES (June 2008) cfmax New set of 4 parameters reflecting cloud vertical structure in the boundary-layer LES (x) vs SCM (y), daily values Evaluated for the time-range 10-14 UTC to capture diurnal variation zcf max overlap ratio

16. Bar-chart Monthly-mean bias for June 2008

17. Impact of including a new cloud overlap function Multi-year bias for 2007-2010 Green: including SGS overlap for cumuliform clouds (Neggers et al, JGR, 2011)

18. Conclusions Multiple parameter evaluation was performed against multi-year Cabauw data RACMO physics was subjected to a 12-point check reflecting the cloud structure, radiative budget and heat budget of coupled boundary-layer soil system This revealed the existence of a compensating error between the representation of cloud vertical structure and cloud overlap in the cumuliform boundary layer