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Verena Grützun , Oswald Knoth, Martin Simmel, Ralf Wolke IfT Leipzig

Oct. 24 th 2006. Spectral microphysics in weather forecast models with special emphasis on cloud droplet nucleation. Verena Grützun , Oswald Knoth, Martin Simmel, Ralf Wolke IfT Leipzig. “Spectral microphysics in weather forecast models”. Introduction. Goals:

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Verena Grützun , Oswald Knoth, Martin Simmel, Ralf Wolke IfT Leipzig

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  1. Oct. 24th 2006 Spectral microphysics in weather forecast models with special emphasis on cloud droplet nucleation Verena Grützun, Oswald Knoth, Martin Simmel, Ralf Wolke IfT Leipzig

  2. “Spectral microphysics in weather forecast models” Introduction • Goals: • Introduction of a spectral microphysics into the Lokalmodell of the German Weather Service. • Investigation of the the influence of aerosols (composition, size distribution, number concentration) on precipitation • Improving quantitative precipitation forecast through offering new approaches to microphysical parameterizations • Status: … Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  3. “Spectral microphysics in weather forecast models” Introduction Work to date: • Implementation of a SPECtral microphysicS (warm and mixed phase) into LM (“LM-SPECS“) • Implementation of conservative advection scheme for moisture variables • Test cases of cloud evolution (Heat bubble, 2D mountain overflow) • Simplified description of CCN evolution in progress • Comparison with two moment microphysical scheme Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  4. u,v,w, p, r, T T, qc, qv Model system LM-SPECS I Theory dynamics tLMk tLMk+1 Advection u,v,w,p,T tLM T(tLMk)+itmpdTdyn (tLMk)+itmpdrdyn Advection qv, nbin, qcbin, qabin, qsbin m tmp p(tLMk)+itmpdpdyn … … microphysics tmp1 tmpm tmpi (=tLMk+1) (=tLMk) Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  5. Model system LM-SPECS II Theory • Combined spectrum of CCN and droplets in (currently) 66 mass-doubling bins • Spherical ice particles in (currently) 66 bins • Number density, total water mass, (frozen water mass,) total aerosol mass, soluble aerosol mass (binwise) • Purely insoluble particles as ice nuclei • Condensation, collision, break-up, contact / immersion / deposition freezing, secondary freezing processes Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  6. Test case: Heat bubble Setup Artificial test case: • Model domain 80 km x 80 km • Horizontal resolution 1 km, 40 vertical layers • Initial wind equal zero • Temperature disturbance of up to 2 K (“Heat bubble“ at the height of 1.4 km, hor. radius 10 km) Sensitivity study w. resp. to initial number distribution NT: NT = 200 cm-3 (N200) NT = 566 cm-3(N566) NT = 4000 cm-3(N4000) Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  7. Results: Heat bubble at 24 min Liquid water content N566 Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  8. Results: Heat bubble at 24 min Particles and relative humidity Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  9. Results: Heat bubble at 24 min Particle spectra 6.4 km 3.7 km 2.9 km Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  10. Results: Heat bubble at 24 min Accumulated rain Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  11. Test case: 2D Mountain Setup Artificial test case: • 2-dimensional mountain overflow, 400 gridpoints in x-direction • Horizontal resolution 2.8 km, 38 vertical layers • Horizontal wind at start:15 m/s • Idealized vertical sounding (Thompson et al., 2004) • Warm-phase microphysics Sensitivity study w. resp. to mountain height, comparison with 2-moment bulk microphysics scheme Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  12. Liquid water content Results: 2D mountain at 6h Height: 500 m polluted clean Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  13. Liquid water content Results: 2D mountain at 6h Clean case 1000m 500m Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  14. Liquid water content Results: 2D mountain at 6h Clean case A. Mühlbauer et al., 2006 500m comparison with 2-mom. scheme Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  15. Precipitation – spatialdistribution Results: 2D mountain at 6h A. Mühlbauer et al., 2006 Spectral microphysics comparison with 2-mom. scheme Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  16. The model system LM-SPECS has been developed, coupling the LM with a spectral microphysics scheme • Sensitivity studies on an artificial heat bubble were done to test the model performance, results: • Spectral information about the development from humid aerosol particles to rain drops; depletion, supersaturation • Strong influence of particle number on accumulated rain: more particles  less & later rain • 2D Mountain test case: Sensitivity study on mountain height, comparison with 2-moment-bulk scheme. • Quantitatively similar results, but differences in cloud structure and resulting distribution of rain Summary Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

  17. Outlook Outlook Second project phase • Improving the mixed phase microphysics • Aiming for realistic episodes, e.g. • Boundary conditions, model nesting • Further comparison with two-moment microphysics, esp. mixed phase microphysics • Improving the numerics & further improvement of realistic runs Perspective: • Case studies with the help of COPS data Verena Grützun, IfT, Modelling Department, Oct. 24th 2006

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