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Das neue COSMO-EU Mikrophysikschema: Validierung von Eisgehalten

Validation study of the new COSMO-EU microphysics scheme focusing on ice content. Changes in snow properties and formation scheme result in slower precipitation formations, leading to higher mixing ratios of cloud water, cloud ice, and snow. The new scheme allows adjustment to different conditions based on temperature and snow mixing ratio, providing more accurate microphysical process rates estimation.

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Das neue COSMO-EU Mikrophysikschema: Validierung von Eisgehalten

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  1. Deutscher Wetterdienst GB Forschung und Entwicklung Das neue COSMO-EU Mikrophysikschema:Validierung von Eisgehalten Axel SeifertDeutscher Wetterdienst, Offenbach Geschäftsbereich Forschung und Entwicklung Referat FE13 “Numerische Modelle” QUEST-Meeting, 14. Dez. 2007, Offenbach

  2. LME cloud ice scheme: Changes with 3.22: • Sticking efficiency (O) • Fall speed of snow (O) • Intercept parameter and geometry of snow (O) • Warm rain scheme (O) Overall effect? • Precipitation formation much slower, especially at cold temperatures. • On average higher mixing ratios of cloud water, cloud ice and snow. QUEST-Meeting, 14. Dez. 2007, Offenbach

  3. f(D) f(D) f(D) old scheme:constant intercept new scheme:variable intercept new scheme:variable intercept N0,s higher qs higher qs higher T D D D lower qs lower qs lower T Variable snow intercept parameter • The snow size distribution can now adjust to different conditionsas a function of temperature and snow mixing ratio. • This will (hopefully) give more accurate estimates of the various microphysical process rates. QUEST-Meeting, 14. Dez. 2007, Offenbach

  4. Variable snow intercept parameter: An empirical parameterization Using a parameterization of Field et al. (2005, QJ) based on aircraft measurements all moments of the snow PSD can be calculated from the mass moment: Assuming an exponential distribution for snow, N0,s can easily be calculated using the 2nd moment, proportional to qs, and the 3rd moment: Now we have parameterized N0 as a function of temperature and snow mixing ratio. QUEST-Meeting, 14. Dez. 2007, Offenbach

  5. Variable snow intercept parameter: (continued) The dominant effect is the temperature dependency, which represents the size effect of aggregation, i.e. on average snow flakes at warmer temperature are larger. This dependency has already been pointed out be Houze et al. (1979, JAS) and is parameterized in many models using N0,s(T). QUEST-Meeting, 14. Dez. 2007, Offenbach

  6. accumulated precipitation in mm Accumulated precipitation 11.01.07 00 UTC, 06h - 30h Surface observations LME, old microphysics LME, new microphysics • Orographic precipitation falls out slower leading to decreased precip amounts at mountain tops and more horizontal advection into the lee mean: 8.1 mm max: 31.5 mm mean: 11.5 mm max: 50.7 mm mean: 10.3 mm max: 36.7 mm QUEST-Meeting, 14. Dez. 2007, Offenbach

  7. IWC Validation with AMF cloud radar During GOP the ARM Mobile Facility is located in the Murg valley The W-band ARM cloud radar can provide an estimate of the IWC using a dBZ-T-retrieval, e.g. the CLOUDNET algorithm. QUEST-Meeting, 14. Dez. 2007, Offenbach

  8. IWC validation with cloud radar For 4 May 2007 the COSMO-EU operational forecast is able to predict the ice water content of a frontal system. Most of the IWC is in the large mode (snow), only a small portion of the mass is in the cloud ice mode. This is consistent with the measurements of Field et al. (2005). QUEST-Meeting, 14. Dez. 2007, Offenbach

  9. IWC validation with cloud radar Operational COSMO-EU LMQ Experiment Re-running the case with a smaller domain leads to a similar result, but with lower IWC. The LMQ experiment was initialized on 1 May from GME anaysis. After that a full data assimilation was run until 4 May 00 UTC. QUEST-Meeting, 14. Dez. 2007, Offenbach

  10. IWC validation with cloud radar LMQ new microphysics LMQ old microphysics 00 UTC runs A comparison of old an new microphysics shows a quite dramatic difference. The old scheme is not able to produce realistic cloud structures and IWC. QUEST-Meeting, 14. Dez. 2007, Offenbach

  11. IWC validation with cloud radar LMQ new microphysics LMQ old microphysics 06 UTC runs Realistic IWC using the new scheme. Very low IWC for the old microphysics scheme. QUEST-Meeting, 14. Dez. 2007, Offenbach

  12. IWC validation with cloud radar LMQ new microphysics LMQ old microphysics A comparison of old an new microphysics shows a quite dramatic difference. The old scheme is not able to produce realistic cloud structures and IWC. QUEST-Meeting, 14. Dez. 2007, Offenbach

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