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KMD Consortium for Small-Scale Modeling (COSMO) Strengths and Weaknesses

KMD Consortium for Small-Scale Modeling (COSMO) Strengths and Weaknesses. Vincent N. Sakwa RSMC, Nairobi. Overview. KMD Runs a 7km COSMO over Eastern Africa Links Trends at global NWP centers Trends in regional NWP General Model information and configuration

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KMD Consortium for Small-Scale Modeling (COSMO) Strengths and Weaknesses

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  1. KMD Consortium for Small-Scale Modeling (COSMO) Strengths and Weaknesses Vincent N. Sakwa RSMC, Nairobi

  2. Overview • KMD Runs a 7km COSMO over Eastern Africa • Links • Trends at global NWP centers • Trends in regional NWP • General Model information and configuration • Show this for those interested • Strengths • Weaknesses

  3. Trends at global NWP centers • In 2012 the resolution of global NWP models will be around 16 km (ECMWF), 20km (DWD, JMA), 25 km (KMA, UKMO) and 30 km (CMC). • In 2020 the resolution of most global NWP models will be around 10km and the number of layers will be around 100 or more • Global NWP centers will use sophisticated, ensemble-based data assimilation systems to derive the initial state of the atmosphere.

  4. Trends in regional NWP • Regional high resolution data assimilation at grid spacing <10km with short data cut-off times using local data not available to global centres. • Convection permitting/resolving models at grid spacing of 2 to 4km without the parameterization of deep convection (e.g. COSMO-DE at DWD). • Data assimilation for convection permitting/resolving models using radar data (e.g. latent heat nudging in COSMO-DE) • Short range regional ensemble prediction systems (SREPS) at grid spacing < 10 km, e.g COSMO-SREPS.

  5. General KMD COSMO • COSMO MODEL RUN SUMMARY • Single Domain ~7km • 434x251 grid points • 60 vertical levels • Model top 50 hPa • Forecast length 72 hours but can do 120 hours • Output frequency is 1 hours • Lateral boundaries updated every 3h (GME)

  6. Model Physics • -two stream radiation scheme (Ritter and Geleyn, 1992) including long- and shortwave fluxes in the atmosphere and at the surface; full cloud - radiation feedback; diagnostic derivation of partial cloud cover (rel. hum. and convection) • Grid-scale precipitation scheme including parameterized cloud microphysics (Doms and Schättler, 1997) • Two different mass flux convection schemes (Tiedtke, 1989 or Bechtold, 2001) differentiating between deep, shallow and mid-level convection • Subgrid-scale orography (SSO) scheme (Lott and Miller, 1997) • Level-2 scheme of vertical diffusion in the atmosphere, similarity theory (Louis, 1979) at the surface • Seven-layer soil model including snow and interception storage

  7. COSMO Dynamics Dynamics : Non-Hydrostatic, fully compressible, advection form. Reference state: hydrostatic, stationary (v=0) Prognostic variables: ‘Cartesian’ wind components u, v, w (spherical base vectors) pressure perturbation p’, Temperature T’ humidity var. q Coordinate systems: rotated geographical coordinates generalized terrain-following height coordinate user-defined vertical stretching

  8. KMD COSMO Strengths • High resolution model run relative to global model • Allows higher horizontal resolution (<7km grid spacing), esp. in mountainous terrain. • Non-hydrostatic model • Theoretically improves forecasts of convection. Convection resolving (<3 km) possible which is necessary to simulate deep convection explicitly • But resolution ~7km requires convective parameterization scheme.(Kain-Fritsch CPS) • Alternate solution to GME • Allows to assess uncertainty based on differences • Sophisticated cloud microphysics scheme including the advection of hydrometeors (rain, snow, graupel) • Much better scalability on massively parallel computer systems.

  9. Strengths • Uses GME for both • Lateral boundary conditions and boundary conditions • COSMO is of finer resolution than the GME • And has different physics • Thus provides alternate solution • Areas of difference provide information about uncertainty • May improve convective forecasts and thus QPF • Represents the atmosp in 3 Dimension

  10. KMD COSMO Weaknesses • Local Area Model • Relies on 6-hour LBC’s from Global model • Uses Global model to initiate forecast • Availability • Run twice daily off GFS 0000/1200 UTC cycle • Forecasts to 72 hours in length takes considerable time to become available • Still mesoscale not in the realm of storm scale (=<3km) • Deep convection still a challenge • Topography issues (surface representation)

  11. General Links • http://www.meteo.go.ke/nwp/cosmo/index.html • http://www.meteo.go.ke/rsmc/products/cosmo

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