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SMC-meeting, Bologna, 05/06. Feb. 2014

Proposed changes for COSMO 5.1 from WG2 Remove ‘hacks’ in the tracer module Adaptation of the RK dynamical core for stochastic physics ‘Targeted diffusion’ to avoid cold pools in narrow valleys Reformulated divergence damping coeff . in new fast waves solver.

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SMC-meeting, Bologna, 05/06. Feb. 2014

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  1. Proposedchangesfor COSMO 5.1 from WG2 • Remove ‘hacks’ in the tracer module • Adaptation of the RK dynamical core for stochastic physics • ‘Targeted diffusion’ to avoid cold pools in narrow valleys • Reformulateddivergencedampingcoeff. in new fast wavessolver SMC-meeting, Bologna, 05/06. Feb. 2014 with verification extensions for SMC-teleconf., 16. April 2014 Michael Baldauf (FE13) M. Baldauf (DWD)

  2. Remove ‘hacks’ in the tracer module A. Roches, O. Fuhrer (MeteoCH) When implementing the new Tracer Module (Roches, Fuhrer (2013) COSMO Tech. Rep.) several decisions had to be made concerning specialized treatment of tracer species. In the first implementation of the Tracer Module, those had been treated with the Metadata functionality of the Tracer Module. However the question arises, if some (or the most) of these special treatments are still necessary. In particular, the following special treatments (‘hacks’) should be removed( from Roches, Fuhrer (2013) COSMO Tech. Rep.): M. Baldauf (DWD)

  3. Remove ‘hacks’ in the tracer module • Fixes concerning the Leapfrog dynamical core: • CLP_10E-12: clip qi to zero, if qi < 10-12 • Fixes concerning the Runge-Kutta dynamical core: • ADD_CLP_ADV: add clipping for sedimenting moisture species (qr, qs, qg) at the end of the advection routine. • BD_0GRAD_FORCED: for the species qi, qr, qs, qg either boundary values are read from a file or the boundary condition (BC) grad=0 is used. In the original code version one of these is done in any case despite the fact, that one can prescribe also other boundary conditions. • DAMP_FORCED: For precipitating species, Rayleigh damping is done in any case, even when a grad=0 BC is prescribed. M. Baldauf (DWD)

  4. Remove ‘hacks’ in the tracer module It is quite difficult to decide, if these measurements are still necessary (they have often been implemented during the development phase and sometimes accidentally remained in the code, even when they are not longer necessary). This is in particular the case if the original developer of the code is not longer available. Therefore often the only one needs real case test runs to decide, if anything strange happens or if the forecast quality suffers. Those extensive tests have been performed by MeteoCH  report by A. Roches and O. Fuhrer. Considering the above mentioned measurements together with these test results, it is recommended to follow their suggestions and to simplify the code by removing these ‘hacks’. documentation: is available (Roches, Fuhrer (2013) COSMO Tech. Rep., Roches, Fuhrer, verification report from 25. Nov. 2013)  recommendation for COSMO 5.1 M. Baldauf (DWD)

  5. Adaptation of the RK dynamical core for stochastic physics L. Torrisi (CNMCA), M. Baldauf (DWD) Goal: separate physical and dynamical tendencies First step: shift call of Coriolis force Has no influence to stability, only small changes in results  recommended for COSMO 5.1 M. Baldauf (DWD)

  6. ‘Targeted diffusion’ to avoid cold pools in narrow valleys M. Baldauf, DWD … occured in a few COSMO-DE-runs around 06 Dec. 2013 in a narrow Alpine valley and even led to a model crash in two 2 EPS-members (parallel routine). Similar ‚cold pools‘ have been reported by MeteoCH. Orography M. Baldauf (DWD)

  7. ‘Targeted diffusion’ to avoid cold pools in narrow valleys Problem: unrealistic strong cooling in an Alpine valley M. Baldauf (DWD)

  8. ‘Targeted diffusion’ to avoid cold pools in narrow valleys Problem: unrealistic strong cooling in an Alpine valley M. Baldauf (DWD)

  9. ‘Targeted diffusion’ to avoid cold pools in narrow valleys Main contributor to the cooling is the horizontal advection: 5th order advection intensifies the ‚ramp‘ x M. Baldauf (DWD)

  10. ‘Targeted diffusion’ to avoid cold pools in narrow valleys Linear advection equation (1-dim.) discretized: Spatial discretisations of the advection operator (order 1 ... 6) (u>0 assumed) upwind 1st order iadv_order=1 centered diff. 2nd order iadv_order=2 iadv_order=3 iadv_order=4 iadv_order=5 ! iadv_order=6 Hundsdorfer et al. (1995) JCP Wicker, Skamarock (2002) MWR M. Baldauf (DWD)

  11. ‘Targeted diffusion’ to avoid cold pools in narrow valleys • Possiblesolutions (1): • upwind 3rd order: thisdoes not deepenthe ‚rampstructure‘ in T;indeeditreducesthecoldpoolrelatively fast,isusedoperationally in COSMO-EU,diadvantage: reducedaccuracy in a convection-permittingsetupispossiblydetrimental (?) • dynamicalbottompressureboundarycondition(A. Gassmann, 2004)ldyn_bbc=.TRUE. (works in both fast wavessolvers)disadvantage: does not matchwiththe Mahrer-Discretisation (introd. planned),mechanismis not clear; does not preventevery ‚coldpool‘ • advectionlimitation (G. Zängl) disadvantage: does not preventfromevery ‚coldpool‘, not efficientenoughin thecurrent form M. Baldauf (DWD)

  12. ‘Targeted diffusion’ to avoid cold pools in narrow valleys Possible solutions (2): • ‚targeted diffusion‘ (analogous to G. Zängl in ICON)criteria: diffusion in a (near bottom) grid point, if T‘ < <T‘environment> – 10Kis applied only in these grid points;reduces a cold pool very quickly and is not active later oncomputation time consumption ~ 0.05% this is a relatively harmless action; recommendation for COSMO 5.1 documentation: a short section will be included in the COSMO Sci. Doc. Part I M. Baldauf (DWD)

  13. ‘Targeted diffusion’ to avoid cold pools in narrow valleys Randbehandlung von p'/ (bzw. von p'/z) am Unterrand: 1.) einseitige finite Differenz (G. Zängl): p'/ = 0p'(ke) + 1p'(ke-1) + 2p'(ke-2) 2.) ‚dynamische untere Druckrandbedingung‘ (A. Gassmann, 2004, COSMO-Newsl.) Aus und folgt eine Bedingung für p'/ .

  14. Reformulated divergence damping coeff. in new fast waves solver M. Baldauf, DWD Problem: model crash in a 7 km setup in the area ‚Oman‘, nearby Iranian mountains (‚Mekran‘) Solution: corrected version of the slope dependent reduction of the divergence damping coefficient (Baldauf, 2013) in a staggered grid. the divergence damping coefficient is critical for model stability  Extensive testing in two longer running experiments at DWD: COSMO-DE: running for 2 months COSMO-EU: running for 1 ½ months without problems. Only small changes in the results documentation: not necessary, current Tech. Report No. 21 is sufficient  recommendation for COSMO 5.1 M. Baldauf (DWD)

  15. Reformulated divergence damping coeff. in new fast waves solver Divergence damping coefficient in COSMO-DE along the Alps (current version) 23 km ~ 10 km ~ 4 km ~ 2 km 0 km M. Baldauf (DWD)

  16. Reformulated divergence damping coeff. in new fast waves solver Divergence damping coefficient in COSMO-DE along the Alps (new version) 23 km ~ 10 km ~ 4 km ~ 2 km 0 km M. Baldauf (DWD)

  17. Example for the influence of ‚targeted diffusion‘ and ‚reform. div. damping coeff‘ 06. Dec. 2013, 21 h forecast, T2m M. Baldauf (DWD)

  18. Example for the influence of ‚targeted diffusion‘ and ‚reform. div. damping coeff‘ 06. Dec. 2013, 21 h forecast, v10m M. Baldauf (DWD)

  19. NUMEX-runs for a longer period COSMO-EU (7 km): Exp. 9537 Simulation period: ‚15.10.-15.12.2013‘ Verification results for period ‚01-30 Nov. 2013‘ M. Baldauf (DWD)

  20. upper air verification (U. Pflüger)

  21. upper air verification (U. Pflüger)

  22. SYNOP-Verif. (U. Damrath) Routine Exp.

  23. SYNOP-Verif. (U. Damrath) Routine Exp.

  24. SYNOP-Verif. (U. Damrath) Routine Exp.

  25. SYNOP-Verif. (U. Damrath) Routine Exp.

  26. SYNOP-Verif. (U. Damrath) Routine Exp.

  27. SYNOP-Verif. (U. Damrath) Routine Exp.

  28. COSMO-DE, Exp. 9536 simulation period: ‚15.10.-31.12.2013‘

  29. upper air verification ‚Nov. 2013‘ (U. Pflüger)

  30. upper air verification ‚Nov 2013‘ (U. Pflüger)

  31. upper air verification ‚Dec. 2013‘ (U. Pflüger)

  32. upper air verification ‚Dec. 2013‘ (U. Pflüger)

  33. Summary • Threeproposedactions • targeteddiffusion on T‘:thissolvescoldpools in steepmountainousregionsnegligibleincrease in computational time • bug-fixedslope-dependentdivergencedampingsolvesstabilityproblems in stronglyirregularterrainwithsteepslopes.nochange in time consumption • smallchange in calling order of Coriolis terms • All actionsdoes not significantlychangetheverificationscores. • Probablythey will comeintothenextversion COSMO 5.0.2

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