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. Process-level evaluation.
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Process-level evaluation at selected grid-points:
Constraining a system of interacting parameterizations through multiple parameter evaluation at Cabauw
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.
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
* 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)
The motivation: problems with a new BL scheme in IFS
Too little cloud cover at noon
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?
Obs vs Model scatterplots of monthly means
RACMO SCM: Control (red) and new (blue) scheme
RACMO 3D in forecast mode (grey)
Expanding to multiple independently-measured parameters that reflect the impact mechanism as illustrated before
Reproduction of observed pattern in variation of monthly-mean
Following degrading correlations in coupled BL – soil system
Cabauw cloud-scenes on 8 days with biggest model difference
Make a list of shallow cu days
positive surface buoyancy flux
LCL below BL top
Total cloud cover < 50%
Evaluation against LES
One month of DALES (June 2008)
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
Monthly-mean bias for June 2008
Multi-year bias for 2007-2010
Green: including SGS overlap for cumuliform clouds (Neggers et al, JGR, 2011)
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