ALARO P hysics developments at LACE

1. Neva Pristov LACE Working group for physisc ALARO Physics developments at LACE

2. ALARO physics package - introduction • continous transition from ARPEGE/ALADIN to AROME (continuity + improvements) • to treat ‘grey-zone’ 3-7 km mesh size • economical computation, numerical efficiency • algorithmic flexibility  good basis for further developments

3. Main developments topics • Radiation • Orographic forcing • Large scale precipitation • Prognostic turbulent scheme • Precipitating convection J-F Geleyn, G. Hello, N. Pristov, Y. Bouteloup, M. Derkova, J. Mašek, A.Trojakova, R. Fournier B. Carty, F. Bouyssel, R. Brožkova, J-F Geleyn, M. Derkova, R. Mladek, J. Cedilnik, D. Drvar, I. Beau B. Carty, J-F Geleyn, R. Brožkova, J. Cedilnik, D. Drvar F. Vana, J. Cedilnik, M. Tudor, J-F Geleyn, A.Simon Luc Gerard, J-M Piriou, D. Banciu, I.Stiperski, R. Brožkova, J-F Geleyn

4. Radiation Aim: • using the current delta-two stream approximation of radiative transfer equation for solar and thermal bands • economical computation (a good quality cost ratio) • better consideration of clouds New features: • new technique for thermal radiative fluxes computation on the basis of Net Exchanged Rate (NER) formalism • gaseous transmition functions for computation of optical depth closer to RRTM scheme • introduction of the complete aerosol model • updating of the cloud optical properties

5. Cloud optical properties • availability of prognostic cloud water calls for more sophisticated treatment of clouds in radiative transfer • static treatment of saturationeffectin old scheme (clouds are too opaque in some circumstances) • new scheme: • coefficients k_abs, k_scat dependent on cloud water content • dynamic treatment of saturation, taking into accountcloud depth and geometry • remain cheap, only two bands: solar and thermal

6. Cloud optical properties – strategy • Dependency of coefficients k_abs, k_scat on cloud water content wasfitted using experimental sample of 7 liquid and 16 ice cloud types • Evaluation of saturation effect in idealized framework: • multi-layer delta-two stream system • only clouds taken into account, gases and aerosols ignored • cloud geometry with random or maximum overlaps between adjacentlayers • atmosphere illuminated from one side by direct flux (solar)or diffuse flux (thermal), reflected and transmitted fluxes evaluated • broadband fluxes diagnosed by summing up monochromatic results computed for several hundred separate wavelengths

7. Cloud optical properties Saturation factor versus optical depth for homogeneous clouds, solar band k_absorbtion k_scatter red – liquid clouds, blue – ice clouds, black – mixed clouds

8. Cloud optical properties parameterized versus reference solar reflectance, sample of non-homogeneous 3 layer clouds new old

9. Cloud optical properties Solar absorbtion new (blue) versus old (red) scheme Problematic peak around model level 20

10. Statistical method for the weighting function in NER parameterized versus computed thermal flux

11. Pseudo-prognostic turbulent scheme pTKE • the turbulent memory of the previous timesteps is kept • the advection and diffusion of TKE are added to the current scheme • more general computation of mixing length • prognostic variable TKE

12. TKE vs pseudoTKE = advection + diffusion + mechanical or shear production/destruction + buoyancy production/consumption + viscous dissipation full pseudo = advection + diffusion + Newtonian relaxation towards stationary solution

13. Academic test with 1D model:GABLS II experiment

14. Mixing length computation - current formulation • Empirical formula dependent on the height of the PBL (Ayotte, et al.1996) Increase of the mixing length with the PBL height (hPBL) = f (z, hPBL) -exponential function Modifications:  1 , 2  = f (hPBL)

15. Tests with the BL89 parameterization • Bougeault-Lacarrère (1989) : “non-local” mixing length dependent on TKE and integral buoyancy (used e.g. in ARPEGE and Mèso-NH) • Direct application of BL89 in the pseudo-TKE scheme: numerically stable but not consistent with the original K-theory part (too large mixing length – increase of exchange coefficients and turbulent fluxes) • Consequences: • systematic increase of TKE and winds at surface, • too big diffusion in the upper troposphere, danger of tropopause erosion

16. Merger with BL89 or TKE/N schemes • current mixing length (GC) taken as a first guess • additional information about TKE and buoyancy from the BL89 scheme, modulation with k-parameter • more suitable for computation of K-coefficients • Merger with TKE/N scheme (only extensively tested, 1-D evolution too noisy, not so good properties)

17. Academic test with 1D model:GABLS II experiment • Vertical profile and time course of mixing length PBL top Modified GC GC+BL89

18. impact in jet-stream area higher TKE in the PBL A B A B 3-D case: strong jet stream 15 December 2005, Northern Germany TKE and  cross-sections only small TKE (no CAT) Modified GC BL89

19. 3-D case: strong jet stream • GC+BL89: more feasible for PBL, TKE signals in jet region (CAT) but not too violent • TKE/N: Too much TKE in upper troposphere GC+BL89 GC+TKE/N

20. Large scale precipitation • a simple micro-physics scheme with 5 water species included into precipitation scheme • cloud water, cloud ice, rain, snow - new prognostic variables • fluxes • statistical approach for sedimentation of rain and snow

21. ALARO-0 minus 3MT 6h precipitation 6h precipitation alaro oper better space distribution of precipitation

22. ALARO-0 minus 3MT Vertical profiles of horizontal averaged values cloud water cloud ice

23. Plans • Evaluation of parameterization developments • Technical and scientific validation • Case studies, verification • Training • Continuation of work • Convection (3MT) • More complex options