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Methodological approach to parameter perturbations in GEM-LAM simulations

Methodological approach to parameter perturbations in GEM-LAM simulations. Leo Separovic, Ramon de Elia and Rene Laprise. MOTIVATION. Sub-grid parameterization schemes describe:

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Methodological approach to parameter perturbations in GEM-LAM simulations

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  1. Methodological approach to parameter perturbations in GEM-LAM simulations Leo Separovic, Ramon de Elia and Rene Laprise

  2. 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 0th hypothesis that the difference is only due to sensitivity to initial conditions.

  3. 2m-Temperature (signal) KFCTRIG(ref)=0.034 KFCTRIG=0.020 (-) KFCTRIG=0.048 (+) DJF MAM MAM DJF K JJA SON JJA SON

  4. 2m TEMP: rejection level 99.9 99.5 99.0 97.5 95.0 90.0 90.0 95.0 97.5 99.0 99.5 99.9 KFCTRIG(ref)=0.034 KFCTRIG=0.020 (-) KFCTRIG=0.048 (+) % DJF MAM MAM DJF JJA SON JJA SON

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