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Implementation of the TKE-Scalar Variance Scheme into the COSMO Model

Implementation of the TKE-Scalar Variance Scheme into the COSMO Model. Ekaterina Machulskaya and Dmitrii Mironov German Weather Service, Offenbach am Main, Germany (ekaterina.machulskaya@dwd.de, dmitrii.mironov@dwd.de). 5 September 2011.

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Implementation of the TKE-Scalar Variance Scheme into the COSMO Model

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  1. Implementation of the TKE-Scalar Variance Scheme into the COSMO Model Ekaterina Machulskayaand Dmitrii Mironov German Weather Service, Offenbach am Main, Germany (ekaterina.machulskaya@dwd.de, dmitrii.mironov@dwd.de) 5 September 2011

  2. Formulation of the TKE-Scalar Variance scheme (recall) The new scheme within a full-fledged COSMO model: implementation, parallel experiment, problems TKE-Scalar Variance scheme and surface heterogeneity: implementation of tile approach and sensitivity experiments Conclusions Outlook Outline

  3. TKE-Scalar Variance Closure Model Transport (prognostic) equations for <ui’2> (kinetic energy of SGS motions) and for <’2> (potential energy of SGS motions) including third-order transport The scalar-variance equation Algebraic (diagnostic) formulations for scalar fluxes, for the Reynolds-stress components, and for turbulence length scale No way to get counter-gradient scalar fluxes in convective flows unless third-order scalar-variance transport is included

  4. TKE-Scalar Variance scheme within the 3d COSMO model TKE-scalar variance scheme is implemented into three-dimensional COSMO model (V4_18) New global 3d-fields: tt_var(ie,je,ke), qt_var(ie,je,ke), qq_var(ie,je,ke) Parallel experiments are being performed (started at 01.07.2011) • Exp 8318 – COSMO-EU (7 km mesh size) • Exp 8351 (assimilation cycle) + Exp 8361 (main runs) – • COSMO-DE (2.8 km mesh size)

  5. TKE-Scalar Variance scheme within COSMO (cont’d) TKE difference (Exp8351 – Routine) at the height 300 m 05.07.2011 10.07.2011

  6. TKE-Scalar Variance scheme within COSMO (cont’d) Temperature gradient difference (Exp8351 – Routine) near the surface 05.07.2011 10.07.2011

  7. TKE-Scalar Variance Scheme and Surface Heterogeneity Blue – homogeneous SBL, red – heterogeneous SBL. LES of stable boundary layer over heterogeneous and homogeneous surfaces by D. Mironov and P. Sullivan (NCAR) Numerous studies show that in convective boundary layer surface heterogeneity also induces large changes in the mixing regime

  8. Enhanced Mixing in Horizontally-Heterogeneous SBL An Explanation increased <’2> near the surface  reduced magnitude of downward heat flux  less work against the gravity  increased TKE  stronger mixing Decreased (in magnitude) Increased Increased downward upward

  9. Coupling of the TKE-Scalar Variance Scheme with the Tiled Surface Scheme Increased <’2> at the surface might be accounted for in: • Use tile approach where different tiles within an atmospheric model grid box have different surface temperature • Surface fluxes are computed as weighted means of fluxes over individual tiles • <w’’2>(Neumann condition) or<’2>(Dirichlet condition) are non-zero at the surface • Transport (prognostic) equation for the temperature variance including third-order transport to carry temperature variance from the surface upward

  10. Coupling of the TKE-Scalar Variance Scheme with the Tiled Surface Scheme s1 Tile 1 s x Tile 2 s2 Surface temperature variations modulate local static stability and hence the surface heat flux z z s2 s1 a a  net gain/loss of <’2> due to non-zero third-order transport term!

  11. Tiled Surface Scheme within the 3d COSMO model • Mosaic approach implemented by Felix Ament into the COSMO version 4.7 →either mosaic or tile approach in the version 4.16, with a user-specified number of tiles or sub-grid mosaic pixels • Number of tiles should not be large (computational efficiency!) • Surface types with the largest difference of thermal inertia should be chosen: lake/land • Grid-scale lakes (lake fraction > 0.5) • are already treated within the COSMO • with FLake model; • there are, however, numerous • subgrid-scale water bodies • (lake fraction < 0.5) • which are ignored: lake fraction

  12. Tiled Surface Scheme within the 3d COSMO model: set up • Parallel experiment 8330 is set up • (COSMO-EU domain, V4_16, running since 01.04.11) • (The information about lake fraction is available within the COSMO model – • no additional software to generate external parameters is needed, • thanks to Uli Schaettler for this idea!) • For sub-grid lakes (lake fraction < 0.5) • lake depth is set to 10 m • on the zero time step, the cold start is performed: • lake surface temperature = MAX( land surface temperature, freezing point ) • lake bottom temperature = +4°C (temperature of maximal water density) • mixing depth = 8 m • ice depth = 0 m • shape factor C_T = 0.5 (default) with 2 tiles: lake/land

  13. Tiled Surface Scheme within the 3d COSMO model: results Difference in surface temperature between lake tile and land tile night, 30.04.2011 00 UTC day, 30.04.2011 12 UTC

  14. Tiled Surface Scheme within the 3d COSMO model: results Difference in surface temperature between experiment with tile approach (mean over two tiles) and control run (no tiles) night, 30.04.2011 00 UTC day, 30.04.2011 12 UTC

  15. The TKE-Scalar Variance scheme is implemented into the COSMO model. The new scheme is being tested through parallel experiments including the entire COSMO-model data assimilation cycle. The coupling between TKE-Scalar Variance scheme and Tiled Surface Scheme is proposed. Tiled Surface Scheme is implemented into the COSMO model and tested through parallel experiments including the entire COSMO-model data assimilation cycle in the configuration of two tiles lakes/land. Conclusions

  16. non-local formulation of turbulence length scale with due regard for phase changes (moist turbulence), based on the work of Veniamin Perov and Oleg Evteev (the work is performed within the framework of the UTSC project) non-Gaussian effects within the SGS statistical cloud scheme, based on the existing recipes (from the literature), results of testing of the COSMO-model SGS statistical cloud scheme by Euripides Avgoustoglou (within the framework of the UTSC project), and the LES-based study of Axel Seifert (the work is underway within the framework of Hans Ertel Centre for Weather Research) Full coupling of the scalar-variance equations to the tiled surface scheme (including modifications to the surface boundary conditions for the scalar variances) to account for the effect of surface heterogeneity on the structure and mixing properties of the PBL (mainly the stably stratified PBL), based on the existing formulations by Matthias Raschendorfer, LES findings by Sullivan and Mironov (2010) and further results expected from co-operative work with Dr. Peter Sullivan of NCAR, and the COSMO-model tiled surface scheme whose development is underway within COSMO community (Ekaterina Machulskaya, Jürgen Helmert, WG3b) Outlook

  17. Thank you for your attention! Acknowledgements: Vittorio Canuto, Peter Bechtold, Sergey Danilov, Evgeni Fedorovich, Jochen Förstner, Vladimir Gryanik, Thomas Hanisch, Donald Lenschow, Chin-Hoh Moeng, Ned Patton, Pier Siebesma, Peter Sulluvan, Jeffrey Weil, and Yun-Ichi Yano.

  18. Stuff Unused

  19. TKE-scalar variance scheme within a full-fledged COSMO model TKE-scalar variance scheme is implemented into full-fledged three-dimensional COSMO model (V4_18) Parallel experiments are performed (all started at 01.06.2011, except for 8318 with re-initialization which is started at 08.06.2011) • without re-initialization: Exp 8318 – COSMO-EU (crushed after 4 days) Exp 8317 – COSMO-DE, assimilation cycle (crushed after 26 days, passed through with the time step = 10s during 26.06, crushed after 29 days, time step doesn’t help, stop) Exp 8346 – COSMO-DE, main runs to 8317 (crushed after 15 days, passed through with the time step = 10s during 15.06, crushed after 21 days, passed through with the time step = 10s during 21.06, 27 days so far) • with re-initialization: • Exp 8318 – COSMO-EU (17 days so far) • Exp 8351 – COSMO-DE, assimilation cycle (crushed after 26 days, passed through with the time step = 10s during 26.06, one month finished) • Exp 8361 – COSMO-DE, main runs to 8351 (crushed after 26 days, passed through with the time step = 10s during 26.06, one month finished)

  20. Enhanced Mixing in Horizontally-Heterogeneous SBL An Explanation Decreased (in magnitude) Increased Increased increased <’2> near the surface  reduced magnitude of downward heat flux  less work against the gravity  increased TKE  stronger mixing downward upward

  21. Tiled Surface Scheme within COSMO: results

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