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PP UTCS Final Status Report

PP UTCS Final Status Report. Dmitrii Mironov German Weather Service, Offenbach am Main, Germany dmitrii.mironov@dwd.de. 13 September 2012. Overview of project results Co-operation with external partners Summary and immediate plans (finalizing the project) A look into the future. Outline.

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PP UTCS Final Status Report

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  1. PP UTCSFinal Status Report Dmitrii Mironov German Weather Service, Offenbach am Main, Germany dmitrii.mironov@dwd.de 13 September 2012

  2. Overview of project results Co-operation with external partners Summary and immediate plans (finalizing the project) A look into the future Outline

  3. Task 2.1: Component testing of COSMO turbulence scheme, revision of surface-layer formulations, COSMO-SC (Matthias Raschendorfer) Results • COSMO-SC version tailored for COSMO-4.24 is developed and is ready for component testing • The new COSMO-SC version includes (i) several bug fixes, (ii) extensions to allow forcing with measured surface fluxes, (iii) extensions to allow forcing the soil moisture calculation with measured evaporation, and (iv) implicit vertical diffusion • Some component tests are performed with COSMO-SC to facilitate the current model development

  4. Task 2.1 (cont’d) Work in progress • A revised formulation of the transfer resistance in the surface-to-atmosphere transfer scheme is developed (not yet implemented) • The code structure is modified to ease the implementation of new formulations • An alternative profile function for stable stratification is implemented in the current test version as an option See the COSMO web site for further details Future plans (new PT, deliverables, deadlines, etc.), c/o Matthias Raschendorfer

  5. Task 2.2: Development and testing of non-local turbulence length scale formulation (Veniamin Perov, Mikhail Chumakov) Results • A non-local parameterization of the turbulence length scale with due regard for the effect on phase changes on the scale of turbulence is developed (cf. Bougeault and Lacarrere 1989) • The new parameterization is included into the module TURBDIFF of COSMO • Numerical experiments show a satisfactory performance of the new length-scale formulation; overall, turbulence and buoyancy fluxes are more intense with (“moist”) mixing length • Numerical experiments are performed with 3D COSMO model for summer days, results are compared with the reference version of COSMO and with the radiosonde and profiler data • Use of non-local turbulence lengths scale formulation improves COSMO performance, e.g. with respect to near-surface temperature and humidity

  6. Task 2.2: Results Vertical profiles of potential temperature computed with the current (blue) and new (red) formulations for the turbulence length scale. Observational data are shown with the black curve.

  7. Task 2.3: Development of a unified turbulence scheme for COSMO, COSMO-SC, and ICON(Matthias Raschendorfer) Results, work in progress Numerous modifications are made to the current COSMO-model turbulence scheme (all modifications are in the private test version c/o MR, some modifications are already a part of the official COSMO code): • bug fixes, stronger modularization and adaptation for use within both COSMO and ICON; • modified positive-definite solution of the TKE equation and the equations for stability functions (a SUBROUTIEN called by ‘turbdiff’ and ‘turbtran’), relaxed restrictions required to guarantee realizability; • updated moist physics (a SUBROUTINE called by ‘turbdiff’, ‘turbtran’, and near surface diagnostics), optional extension to allow for mixed water-ice phase; • new generalized scheme for semi-implicit vertical diffusion (called for each diffused variable, incl. TKE and passive tracers, without code replication), options for explicit treatment of tendencies, gradient corrections, and lower boundary condition.

  8. Task 2.3 (cont’d) Results, work in progress • Explicit non-gradient flux corrections are introduced (e.g. SGS condensation correction and the circulation term are now expressed as a gradient correction within the new vertical diffusion scheme) • Optional stability correction of turbulent master length scale is implemented (already in official code) • A concept of scale separation is developed, three optional scale-separation terms related to SSO wakes, convective plumes, and horizontal shear eddies are introduced into the prognostic TKE equation (already in official code, SSO term is operational at DWD) • Analytical work is performed on a scale-dependent mass-flux convection scheme interacting with the turbulence scheme

  9. including horizontal shear – and SSO-production reference pot. temperature [K] including horizontal shear –, SSO- and convective production DWD Matthias Raschendorfer COSMO Lugano 2012

  10. Task 3: Evaluation of Relative-Humidity and Statistical Cloud Schemes against Observational Data (Euripides Avgoustoglou) Results • Performance of relative-humidity (RH) and statistical cloud schemes (incl. version with water-ice mixed phase) is assessed using satellite and in-situ observations (taken over the Greece-centered domain) • Minimum T2m is better predicted by the statistical scheme, and vice versa for maximum T2m • Statistical scheme leads to stronger underestimation of low cloud cover than RH scheme • Medium clouds are somewhat better predicted by statistical scheme • As the Task 3 results suggest, statistical scheme cannot replace the default RH scheme (in radiation calculations)

  11. Task 3: Results (cont’d) Minimum T2m 28 April 2011.

  12. Task 3: Results (cont’d) Low cloud cover computed by the COSMO model with statistical (yellow) and RH (magenta) cloud schemes vs. satellite data (blue)

  13. Task 3: Results (cont’d) Medium cloud cover computed by the COSMO model with statistical (yellow) and RH (magenta) cloud schemes vs. satellite data (blue)

  14. Task 1: Development, Testing and Implementation into COSMO of the TKE-Scalar Variance Mixing Scheme (Ekaterina Machulskaya and Dmitrii Mironov) TKE-Scalar Variance (TKESV) scheme for COSMO is developed • Apart from the TKE equation, the new scheme carries prognostic equations for variances of the liquid water potential temperature variance and the total water specific humidity variance and θl-qtcovariance • Prognostic variance equations include turbulent diffusion terms (divergence of triple correlations) • Reynolds stress and scalar fluxes are determined through algebraic diagnostic expressions (incl. turbulence anisotropy) • Scalar-flux formulations include non-gradient terms • Turbulence length (time) scale depends on static stability

  15. Task 1: 1D Results • TKESV scheme is favourably tested through single-column numerical experiments (outperforms one-equation TKE scheme) • Dry PBL: enhanced mixing, up-gradient heat transfer • Cloudy PBLs (shallow cumuli, stratocumuli): better prediction of scalar variances and TKE, slight improvements with respect to the vertical buoyancy flux and the mean temperature and humidity

  16. Potential temperature minus its minimum value within the PBL. Black dotted curve shows LES data (Mironov et al. 2000), red – TKE scheme, blue – TKESV scheme. Mean Temperature in Convective PBL TKE and TKESV Schemes vs. LES Data Task 1: 1D Results (cont’d) Enhanced mixing, counter-gradient heat transfer

  17. Task 1: 1D Results (cont’d) TKE (left panel) and <’2> (right panel) made dimensionless with w*2 and *2, respectively Black dotted curves show LES data, red – TKE scheme, blue – TKESV scheme.

  18. Task 1: 1D Results (cont’d) Potential temperature variance (two left panels) and total water variance (two right panels) for BOMEX (shallow cumulus test case). Red – TKE scheme, blue – TKESV scheme. Black solid curves in the middle figures show LES data.

  19. Task 1: 3D Results • TKESV scheme is implemented into COSMO • The scheme is tested through a series of parallel experiments, results look promising • Verification against observations indicate improvements as to e.g. fractional cloud cover and 2m temperature and humidity

  20. TKESV vs. ROU COSMO-DE, July-November 2011 (EXP, ROU) August September Oct-Nov July 2m temperature bias 2m dew point bias

  21. TKESV vs. ROU 2m temperature RMSE 2m dew point RMSE July 2011 August 2011 July 2011 August 2011 Low clouds, July 2011

  22. TKESV + reduced Kmin vs. ROU COSMO-DE, 1 July – 30 September 2011 (EXP, ROU) 2m dew point 2m temperature Low clouds

  23. TKESV + reduced Kmin + new aerosols vs. Kmin + NA COSMO-DE, 1 June – 31 July 2012 (TKESV) 2m temperature Low clouds

  24. Task 1: Remaining Problems Overestimation of fractional cloud cover in cumulus-topped PBL • This error is attributed primarily to the shortcomings of quasi-Gaussian statistical cloud scheme which is unable to describe cumulus regime. A somewhat more sophisticated cloud scheme that accounts of non-Gaussian effects is required (see below). Skewness-dependent “diffusion + advection” parameterizations of the third-order moments in the scalar-variance equations • The skewness-dependent parameterizations are developed, tested through single-column experiments, and are available as an option within the TKESV scheme. These parameterizations reduce numerical stability of the entire scheme (smaller time step is required) and are not recommended for immediate implementation into COSMO (cf. three-moment SGS cloud scheme).

  25. We Should Acknowledge Witold Interewicz For his on the COSMO-model cumulus convection (e.g. attempts to slow down deep convection) Balázs Szintai For his work on component testing of the COSMO-model turbulence scheme (e.g. improved parameterization of the TKE vertical transport)

  26. Co-operation with External Partners DWD – NCAR (USA) Co-operation • “Mixing in stably-stratified boundary layers over heterogeneous surfaces: large-eddy simulation, second-moment budget analysis, and parameterization”, Peter Sullivan (NCAR) “Extramurale Forschung” (EMF) Program of DWD and German Universities • “Development and testing of a scale independent convection parameterisation for ICON”, Richard Keane, George Craig and Christian Keil (University of Munich) • “High-resolution large-eddy simulation of atmospheric boundary-layer turbulence – contribution to the improvement of turbulence parameterisations through systematic study of higher-order statistical moments and their budgets”, Rieke Heinze and Siegfried Raasch (University of Hannover)

  27. LES-Based Study of SBL over Heterogeneous Surfaces (Mironov & Sullivan): Motivation Mixing is typically underestimated Models tend to quench turbulence in strongly stable stratification Ad hoc tuning devices like “minimum diffusion coefficients” do not help much (they are often detrimental for the NWP/climate model performance) Models of stably stratified PBL, incl. surface layer, do not account for many important features (e.g. gravity waves, meanders of cold air, radiation flux divergence, and horizontal heterogeneity of the underlying surface)

  28. Enhanced Mixing in Horizontally-Heterogeneous SBL: An Explanation (Mironov and Sullivan 2010) increased <’2> near the surface  reduced magnitude of downward heat flux  less work against the gravity  increased TKE  stronger mixing Increased Decreased in magnitude Increased

  29. How to Account for Surface Heterogeneity? Blue – homogeneous SBL, red – heterogeneous SBL. • Enhanced mixing is due to increased temperature variance close to the surface (see Mironov and Sullivan 2010, for details) • For want of a more elegant theory, use tile approach where the number of tiles should not be large (otherwise computationally expensive) but account for tiles with a maximum difference in terms of thermal inertia • SGS water is crucial

  30. TKESV Scheme and Tiled Surface Scheme • Tile approach where different tiles have different surface temperature (the mosaic scheme coded by Felix Ament was used as starting point) • Surface fluxes are computed as weighted means of fluxes over individual tiles • Transport (prognostic) equations for TKE and for the scalar variances including third-order transport of scalar variance • <’2>, <w’’2>, <q’2> and <w’q’2> determined with tiled scheme (non-zero at the surface!) are used as lower boundary conditions for scalar variances • (i) Off-line single-column tests • (ii) COSMO test runs using tiled surface scheme with due regard for SGS water

  31. TKESV + Tiled Surface Scheme: Off-line Test Blue – homogeneous SBL, red – heterogeneous SBL.

  32. COSMO Test Runs • COSMO-EU, the lake parameterisation scheme FLake is used to model inland water bodies • External-parameter fields of lake fraction and lake depth are generated using the updated lake-depth data set (Kourzeneva 2010) and the software package by Hermann Asensio • For grid boxes with 0.05<FR_LAKE<0.5 (SGS water), the surface fluxes are computed as weighted mean over two tiles, water and land • All SGS inland water bodies are 10 m deep (external-parameter software should be modified to use the actual depth where available)

  33. COSMO Test Runs: Results The lake-fraction external-parameter field based on the lake-depth data from Kourzeneva (2010) and GlobCover physiographic data. The horizontal size of the COSMO-model grid is ca. 7 km.

  34. COSMO Test Runs: Results (cont’d) Difference in surface temperature between experiment with tile approach (mean over two tiles) and control experiment (no tiles) night, 30.04.2011 00 UTC Warming due to SGS lakes day, 30.04.2011 12 UTC Cooling due to SGS lakes

  35. COSMO Test Runs: Results (cont’d) Control run (no tiles) Experiment (two tiles) T2m warm bias is reduced

  36. Development and testing of a scale independent convection parameterisation for ICON (EMF) Motivation • Improve representation of convection in NWP models (diurnal cycle, meso-scale organisation, momentum transport) • Account for a highly variable (stochastic) convective activity within grid cells Results • The Plant and Craig (2008) stochastic convection scheme is implemented into ICOSN and COSMO, the scheme is adapted to become “GCM-independent” • Test simulations with ICON and COSMO are performed Outlook • Improve the scheme computational efficiency (vectorization, etc.), work is underway • Perform further comprehensive tests

  37. Precipitation Variability Probability distribution of precipitation intensity (between 10S and 10N) for six different ICON runs.

  38. Example rainfall snapshots for three different convection schemes in COSMO The rainfall variability is closer to that of reality with the Plant-Craig scheme, as compared to two different conventional schemes.

  39. High-Resolution Large-Eddy Simulation of Atmospheric Boundary-Layer Turbulence (EMF) Motivation • In spite of numerous LES of PBL turbulence, no comprehensive analysis of the second-moment budgets for cloudy boundary layers • Budgets are required to (i) estimate relative importance of the various terms, (ii) test and further develop turbulence parameterizations, (iii) determine disposable parameters Results • Budgets in clear and cloudy boundary layers are analysed on the basis of very high resolution LES • Pressure-scrambling terms in the Reynolds-stress and scalar flux equations are analysed (not possible with observational data!) Outlook • Use LES-based results to develop mixing schemes for NWP (and climate) models • Estimate disposable parameters of mixing schemes

  40. BOMEX (shallow cumulus case): TKE and its budget

  41. BOMEX: Total Water Variance and Its Budget

  42. BOMEX: Temperature Flux and Its Budget !!!

  43. Heinze, R., D. Mironov, and S. Raasch, 2012: Budgets of scalar fluxes for cloudy boundary layers. Proc. 20th Amer. Meteorol. Soc. Symp. on Boundary Layers and Turbulence, Boston, MA, USA, paper 11.4, 9 pp. BOMEX and DYCOMS-II (stratocumulus case): pressure-scrambling • Analysis of the pressure-scrambling components is not possible on the basis of observational data • Detailed knowledge of pressure terms is necessary to estimate disposable constants of the second-order schemes and to reduced the number of constants to be tuned Rieke Heinze received the 1st prize (“Outstanding Student Presentation Award”) for her presentation at the 20th AMS Boundary Layers and Turbulence Symposium, Boston, MA, USA, 9-13 July 2012.

  44. The project ends in September 2012. During the coming months (09-12.2012): inclusion of modifications associated with the TKESV scheme into the official COSMO code. N.B. As the current version of TKESV is not coded as a separate module, new features are implemented into the COSMO TKE scheme. Since massive modifications to the current TKE scheme are prepared by Matthias Raschendorfer and should soon be included into the official COSMO code, modifications associated with the TKESV scheme will be implemented into the COSMO version following the version with Matthias’ changes. The implementation process will be controlled by the COSMO source code administrator. Documentation of the TKESV scheme is in preparation. Summary and Immediate Plans

  45. Development of a three-moment (mean, variance, and skewness) statistical SGS cloud scheme that accounts for non-Gaussian effects. Co-operation with Axel Seifert and Ann Kristin Naumann, Hans Ertel Centre on Cloud and Convection (HErZ), Hamburg. Work is well underway. A Look into the Future

  46. Further development and comprehensive testing of transport equations for the skewness of scalar quantities, coupling the skewness equations with the three-moment statistical cloud scheme. Much work is already done. Closure assumptions for the scalar skewness equations are formulated and tested within the framework of PP UTCS. Furthermore, skewness-dependent “diffusion+advection” parameterizations of the third-order moments in the scalar-variance equations are developed and tested through single-column experiments (optional within the TKESV scheme). These are, however, not recommended for the immediate implementation into COSMO due to numerical stability problems. However, the scalar skewness equations decoupled from the third-order transport of scalars but coupled to the statistical SGS cloud scheme is a viable option. A Look into the Future (cont’d)

  47. Improved coupling of the scalar-variance equations to the tiled surface scheme to better account for the effect of surface heterogeneity on the PBL structure and mixing (Mironov and Sullivan 2010), use of PBL scalar variances in stochastic parameterizations. Co-operation with Peter Sullivan, NCAR. Effort will go into the analysis of various flow regimes over heterogeneous surfaces (e.g. temperature-heterogeneous flat surface versus temperature-homogeneous surface with orographic features), and into the formulation of the surface boundary conditions for the scalar variances with due regard for the surface heterogeneity. A Look into the Future (cont’d) Results from future efforts will be reported to COSMO through the WG3a.

  48. Thank you for your kind attention! Acknowledgements: Peter Bechtold, Vittorio Canuto, George Craig, Ulrich Damrath, Sergey Danilov, Evgeni Fedorovich, Jochen Förstner, Jean-Francois Geleyn, Federico Grazzini, Vladimir Gryanik, Thomas Hanisch, Rieke Heinze, Richard Keane, Donald Lenschow, Chin-Hoh Moeng, Ned Patton, Robert Plant, Siegfried Raasch, Bodo Ritter, Harald Ruppert, Ulrich Schättler, Axel Seifert, Pier Siebesma, Alan Shapiro, Peter Sullivan, Jeffrey Weil, Jun-Ichi Yano

  49. …

  50. Some Lessons Learnt • Considering high complexity of the problem, a remote mode operation is often inefficient (e.g. the project leader cannot keep an eye on the details of the implementation of all tasks) • “Priority Project/Task” is not necessarily the best way to organise work, particularly work of innovative character

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