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LM Physics Overview and Outlook

LM Physics Overview and Outlook. Marco Arpagaus. 28 th EWGLAM and 13 th SRNWP Meeting Zurich, 9-12 October 2006. Radiation. Scheme: δ-two stream radiation scheme after Ritter and Geleyn (1992) for short- and long-wave fluxes; full cloud-radiation feedback. Recent Extensions:

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LM Physics Overview and Outlook

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  1. LM PhysicsOverview and Outlook Marco Arpagaus 28th EWGLAM and 13th SRNWP MeetingZurich, 9-12 October 2006

  2. Radiation Scheme: • δ-two stream radiation scheme after Ritter and Geleyn (1992) for short- and long-wave fluxes; full cloud-radiation feedback. Recent Extensions: • Quasi-3d: Inclusion of 3d orographic effects on radiation (shadowing, slope angle, slope aspect, sky view). • Upscaling: Use of coarser horizontal mesh to run the 1d radiation scheme in favour of running the scheme more often (aim: use 2*2 grid-points and reduce update frequency from hourly to every 15 min).

  3. Radiation:Quasi-3d and upscaling Average solar surface radiation budget since forecast start (4 April 2005 00 UTC + 8 hrs) original LM grid (2.8 km mesh-size) difference plot: version with topographic corrections minus version without topographic corrections coarser (2x2) grid W/m2

  4. Grid-scale clouds and precipitation Operational schemes: • Cloud-icescheme: 5-class (vapour, cloud-water,cloud-ice,rain, and snow) single-moment scheme. • Graupelscheme: 6-class(vapour, cloud-water,cloud-ice, rain, snow, andgraupel) single-moment schemefor convection-resolving scales. Additional schemes: • Seifert-Beheng (2006): 6 class two-moment scheme • Reisner-Thompson (2004): 6 class single-moment scheme

  5. Grid-scale clouds and precipitation: Graupel scheme Problem: underestimation of precipitation amounts for convection-resolving LM. Cure:Use hail instead of graupel (as suggested by studies of idealised strong convection)?  No! LM (2.8 km mesh-size), 7 August 2004 rg 0.9 g/cm3 N0 = 4*104 m-4 rg 0.2 g/cm3 N0 = 4*106 m-4 radar

  6. Grid-scale clouds and precipitation:Prognostic precipitation Problem: Orographic luv/lee pattern of precipitation. (Partial) solution: full prognostic treatment of precipitating hydrometeors (e.g., rain, snow, and graupel). LM – radar; north-westerly flow only (7 km mesh-size) 2005 2004

  7. Convection:For 7 km mesh-size or larger … • Operational: Tiedtkemass-flux scheme (1989); closure based on moisture convergence. • Options: • Tiedtke scheme with CAPE closure. • Kain-Fritsch mass-flux scheme (1993) by Kain. • Recently tested: Kain-Fritschmass-flux scheme by Bechtold (2001), with closure based on CAPE. • Results: • Improved diurnal cycle (over flat terrain). • Spin-up problem. • (Stronger) overestimation of precipitation amounts, especially for light precipitation.  Code no longer maintained (???). – Test of IFS scheme instead?

  8. Convection:For convection-resolving scales … Noparameterisation scheme for (deep) convection. This however generates a serious problem: • Boundary layer too moist. • Low cloud cover too high.  Insufficient transport of moisture through top of the boundary layer! Quick solution: Use of Tiedtke scheme for shallow convection only. Envisaged long-term solution: Unification of turbulence and shallow convection scheme.  UTCS project.

  9. Turbulence • 2nd-order one-equation closure scheme: prognostic TKE, algebraic relations for other 2nd-order moments. Included are: • subgrid-scale condensation and evaporation (moist conservative variables); • effect of subgrid-scale horizontal inhomogeneity of the underlying surface (additional source of TKE, most notably in the stably stratified PBL). • Surface-layer transfer scheme with a laminar-turbulent roughness sub-layer. • Extensions: UTCS project.

  10. Lower boundary condition: Known surface types in LM A grid box is covered completely by either sea / sea ice:externally prescribed surface temperature; constant during integration land:soil temperature and water content predicted by soil and vegetation model TERRA rock or ice:impermeable for water; temperature profile simulated by TERRA lake:prognostic surface temperature (water or ice) forecasted by lake model Flake

  11. Two-layer TERRA (old) Multi-layer TERRA (new) Interception Interception Snow Snow * 0.01 m * 0.1 m * * * prescribed T 0.81 m 1.0 m * no water flux 2.43 m free drainage 7.29 m constant T Multi-layer soil and vegetation model Modification for thermal part:solution of heat conduction equationinstead of extended force restore method  arbitrary number (and thickness) of soil layers freezing/melting of soil water included (improved T2m in Winter)  simpler lower boundary condition

  12. Multi-layer soil and vegetation model Further modifications: • thermal part: • simplified treatment of melting snow • time-dependent snow density( [50, 400] kg/m3;to reduce negative T2m bias over snow) • dependence of snow albedo on time and forest cover( [0.7, 0.2]; to reduce negative T2m bias over snow) • hydrological part: • new lower boundary condition (no water flux  gravitational drainage) Problems: • soil dries out (especially lower layers)

  13. New: Lake Model ‚FLake‘ (D. Mironov et al., see http://nwpi.krc.karelia.ru/flake) A computationally-efficient lake parameterisation scheme based on the idea of self-similarity (assumed shape, similar to the mixed-layer idea) of the evolving temperature profile. Prognostic variables are … • the surface temperature, • the mean temperature of the water column, • the bottom temperature, • the mixed-layer depth, • the depth within bottom sediments penetrated by the thermal wave, and the temperature at that depth (bottom sediment module may be switched off). … plus in case of ice-covered lake • the ice thickness, • the temperature at the ice upper surface, • the snow thickness, and the temperature at the snow upper surface (in the present pre-operational configuration, snow is treated in a simplified way).

  14. New: Lake Model ‚FLake‘ LM test suite:Lake Balaton, 2006 Single column test:Kossenblatter See, June 1998 lake surface temperature testoperational (SST analysis) FLakeobservations ice thickness FLake is able to simulate diurnal as well as seasonal variations of lake surface temperature (T of water surface or of ice surface) realistically!

  15. Lower boundary condition: New developments • Urban model • development within the FUMAPEX project • Mosaic & tile approach • is currently being implemented • Measurement derived soil moisture analysis • based on a standalone version of TERRA • driven by observations

  16. COSMO Priority Projects • UTCS: Towards a Unified Turbulence Shallow Convection Parameterisation  talk by Dmitrii Mironov • QPF: Tackle deficiencies in Quantitative Precipitation Forecasts

  17. Quantitative Precipitation Forecasts Aim: Study LM (7 km mesh-size) deficiencies concerning QPF by running sensitivity experiments on a series of well chosen cases with poor model performance.  Results expected by September 2007. 18 March 2005

  18. To conclude … • More information: Scientific documentation available on COSMO web-site at http://www.cosmo-model.org/public/documentation.htm. • Acknowledgements: All COSMO members, especially colleagues of Working Group 3 ‘Physical Aspects’. • Thank you for your attention!

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