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Methodological approach to parameter perturbations in GEM-LAM simulations. Leo Separovic, Ramon de Elia and Rene Laprise. MOTIVATION. Sub-grid parameterization schemes describe: - PowerPoint PPT Presentation
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Methodological approach to parameter perturbations
in GEM-LAM simulations
Leo Separovic, Ramon de Elia and Rene Laprise
MOTIVATION• Sub-grid parameterization schemes describe:
- well-known processes that can be exactly represented (e.g. radiation transfer) but need to be approximated so that they do not take excessive computational time;
- less-well understood processes (e.g. turbulent energy transfer) that are situation dependent; parameters in such parameterizations rely on mixture of theoretical understanding and empirical fitting;
• Parameters’ values are uncertain due to measurement errors and problems with their “representativity”; hence the tuning cannot completely eliminate the model error.
• We develop methodological approach to quantify the parametric uncertainty in RCM seasonal simulations. To this end we study the response of GEM-LAM seasonal climate to multiple perturbations of parameters. The perturbations’ size are within a range of uncertainty specified by the experts that participated in the model tuning. GEM-LAM (0.5deg, ERA40) is ran over 1 year and the response is studied for each of the 4 seasons.
• For each combination of parameters a small ensemble with perturbed initial conditions is run in order to estimate the statistical significance of the response.
- the following slide shows the changes in 2m temperature (signal) induced by two singleton perturbations of the threshold vertical velocity in Kain-Fritch convection;
- the second slide shows the rejection level of the 0 th hypothesis that the difference is only due to sensitivity to initial conditions.
2m-Temperature (signal)
DJF MAM
JJA SON
DJF MAM
JJA SON
KFCTRIG=0.020 (-) KFCTRIG=0.048 (+)
K
KFCTRIG(ref)=0.034
2m TEMP: rejection level
DJF MAM
JJA SON90.0
95.0
97.5
99.0
99.5
99.9
99.9
99.5
99.0
97.5
95.0
90.0
DJF MAM
JJA SON
KFCTRIG=0.020 (-) KFCTRIG=0.048 (+)
%
KFCTRIG(ref)=0.034