UTCS PP Status Report Dmitrii Mironov German Weather Service, Offenbach am Main, Germany COSMO General Meeting, Krakow, Poland September 2008

Outline UTCS PP: overview of results, plan for the next COSMO year (Dmitrii Mironov, 15 min) Component testing of the COSMO model turbulent diffusion scheme (Balazs Szintai, 15 min) Development of the two-equation second-order turbulence-convection model (Ekaterina Machulskaya and Dmitrii Mironov, 15 min)

Task 1a: Ekaterina Machulskaya and Dmitrii Mironov Goals Development and testing of a two-equation model of a temperature- stratified PBL Comparison of two-equations (TKE+TPE) and one-equation (TKE only) models Key issues Parameterisation of the pressure terms in the Reynolds-stress and the scalar-flux equations Parameterisation of the third-order turbulent transport in the equations for the kinetic and potential energies of fluctuating motions Realisability, stable performance of the two-equation model Expected outcome Counter gradient heat flux in the mid-PBL Improved representation of entrainment at the PBL top

Mean Temperature in Shear-Free Convective PBL One-Equation and Two-Equation Models Red – one-equation model, green – two-equation model, blue – one-equation model with the Blackadar (1962) formulation for the turbulence length scale. Black curve shows the initial temperature profile. Potential temperature minus its minimum value within the PBL. Black dashed curve shows LES data (Mironov et al. 2000), red – one-equation model, green – two-equation model, blue – one-equation model with the Blackadar (1962) formulation for the turbulence length scale.

Task 1b: Balazs Szintai Goals Comprehensive component testing against LES and observational data of the current COSMO-model one-equation turbulence scheme Key issues Stable performance of the scheme Entrainment at the boundary layer top Expected outcome Improved understanding of the current COSMO-model turbulence scheme Recommendations towards the scheme improvement

Component Testing  Results Turbulent transport of TKE is too weak Negative buoyancy flux at PBL top is practically missing Horizontal velocity variances are poorly described at the PBL top and near the surface Shear-free convective PBL (LES of Mironov et al. 2000) COSMO LES

Task 3a: Euripides Avgoustoglou Goals Testing the existing sub-grid scale statistical cloud scheme to assess whether that scheme could be used by both the turbulence scheme and the radiation scheme of the COSMO model Key issues Consistency with the microphysics scheme (in particular, when the cloud ice is present) Removing ad hoc ”stopgap” formulations from the COSMO-model code Tuning as needed to harmonise the sub-grid scale cloudiness and the radiation calculations Expected outcome A more consistent treatment of the sub-grid scale cloudiness within the COSMO model (eventually, an improved prediction of partial cloud cover and of the surface heat budget)

Total Cloud Cover 12+18hs [GME Analysis 01Jan05 12UTC] gridsubgridsubgrid0 subgridCHsubgridCH1subgridE- 7 subgridR2subgridR4subgridR6 © METEOSAT MSG/IR_10.8um/ :00 UTC % MSG/IR_08.7um/ :00 UTC © METEOSAT

Task 3a: Results In case the COSMO-model SGS statistical clouds scheme is used in both the turbulence scheme and the radiation scheme of the COSMO model, the (diagnosed) cloud cover is compares favourably with satellite data (at least in the simulations performed) The statistical SGS cloud scheme shows quite some potential … although further testing, and most likely tuning, is needed (see presentations of Euripides Avgoustoglou and Matthias Raschendorfer)

Task 4: Witold Interewicz Goals Testing modifications in the COSMO-model deep convection scheme (Tiedtke 1989) Modifications Convective trigger function is modified to account for the bulk properties of the sub-cloud layer Formulations of turbulent entrainment and detrainment rates are extended to account for the updraught-environment buoyancy difference Expected outcome Better coupling of cumulus convection scheme with the other COSMO-model schemes Deep convection schemes is optimised (slowed down, in particular, to perform reasonably as the resolution is refined)

Task 4: Results A modified convective trigger function and extended formulations of turbulent entrainment and detrainment rates that account for the updraught-environment buoyancy difference are implemented into the COSMO-model code Preliminary tests are performed; r esults indicate that an extended E/D formulation suppresses convection somewhat too strong – parameter tuning is needed The work is delayed, it will be completed by the end of 2008

Task 4 (cont’d): Dmitrii Mironov and Axel Seifert Goals Testing modifications in the COSMO-model deep convection scheme (Tiedtke 1989) Modifications the relative humidity threshold for the evaporation of convective precipitation in the sub-cloud layer is set to 80% (95% in the current operational formulation) cloud water-cloud ice mixed phase in convective clouds is allowed over a certain temperature range (current formulation: convective-cloud condensate is either water or ice, depending upon the air temperature being higher or lower than the water freezing point) detrained convective-cloud condensate is saved as tendencies of the cloud water and of the cloud ice, these tendencies are then passed to the COSMO-model physics and dynamics schemes for further processing (current formulation: instantaneous evaporation of detrained convective-cloud condensate) Expected outcome Improved prediction of heavy precipitation Better coupling of cumulus convection scheme with the other COSMO-model schemes The above modifications are now operational at DWD (see the presentation of A. Seifert and D. Mironov at WG3 session)

Problems Apart from a number of scientific problems which are inherent in any innovative effort.... Task 2b Detailed investigation of the cloud-radiation interactions, turning of the radiation scheme as needed (NN) Task 3 Comparison of the cloud condensate predicted by the sub-grid scale cloud schemes (statistical and relative-humidity) and by the grid-scale saturation adjustment procedure (Liliana Velea) No resources have been available to perform these tasks. The tasks have been suspended.

Plan for the Next COSMO Year Task (i). Dmitrii Mironov and Ekaterina Machulskaya Consolidation of a two-equation closure model, including transport equations for the turbulence kinetic energy (TKE) and for the potential temperature variance, of a temperature-stratified planetary boundary layer (PBL) [based on the results obtained in the framework of the UTCS project by September 2008] Development, coding and testing against large-eddy simulation (LES) and observational data of a second-order closure model of a moist PBL, including transport equations for the TKE and for the scalar variances (ice-liquid water potential temperature, total water specific humidity) and a sub-grid scale (SGS) statistical cloud scheme for non-precipitating clouds Comparison of a new model (prognostic equations for the TKE and for the scalar variances) with a one-equation model (prognostic equation for the TKE only)

Plan for the Next COSMO Year Task (i). Veniamin Perov Implementation and testing within the framework of both the one- equation (current COSMO-model formulation) and the two-equation turbulence schemes of a non-local turbulence length-scale formulation (based on Bougeault and Lacarrere, 1989, formulation that accounts for the effect of “remote zones” on the length scale at a given level) Task (i). Matthias Raschendorfer Development and testing of an extended SGS cloud scheme (based on the analysis of current literature and of the existing COSMO-model SGS statistical cloud scheme)

Plan for the Next COSMO Year (cont’d) Task (ii). Balazs Szintai Comprehensive component testing against LES and observational data of the existing COSMO-model one-equation turbulence scheme (prognostic equation for the TKE only) Comparison of a one-equation model (prognostic equation for the TKE only) with a new model Task (iii). Euripides Avgoustoglou Further testing and tuning of the existing COSMO-model sub-grid scale statistical cloud scheme with due regard for the cloud water- cloud ice mixed phase

Plan for the Next COSMO Year (cont’d) Task (iv). Liliana Velea and Aurelia Lupascu Comparison of the cloud condensate predicted by the sub-grid scale cloud schemes (statistical and relative-humidity) and by the grid-scale saturation adjustment procedure. Task (v). Witold Interewicz Consolidation of a modified Tiedtke (1989) cumulus convection schemes including (i) a modified convective trigger function (that should account for the bulk properties of the sub-cloud layer), and (ii) extended formulations of turbulent entrainment and detrainment rates (that should account for the updraught- environment buoyancy difference) [based on the results obtained in the framework of the UTCS project by September 2008] Investigation of the interaction of the parameterised cumulus convection and the grid-scale dynamics within the COSMO model NB! This would better qualify as a Priority Task within the framework of the Working Group 3.

Thanks for your attention!

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Plan for the Next COSMO Year Task (i). NN Later: examination of critical (and possibly dangerous) issues related to the simultaneous use of an SGS statistical cloud scheme and of prognostic equations for the grid-scale cloud water and cloud ice (Tompkins 2002, 2005)