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

2. QUEST-Meeting, 14. Dez. 2007, Offenbach 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.

3. QUEST-Meeting, 14. Dez. 2007, Offenbach Variable snow intercept parameter  The snow size distribution can now adjust to different conditions as a function of temperature and snow mixing ratio.  This will (hopefully) give more accurate estimates of the various microphysical process rates. higher qs lower qs new scheme: variable intercept f(D) D higher T lower T new scheme: variable intercept f(D) D higher qs lower qs old scheme: constant intercept f(D) D N 0,s

4. QUEST-Meeting, 14. Dez. 2007, Offenbach 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, N 0,s can easily be calculated using the 2 nd moment, proportional to q s, and the 3 rd moment: Now we have parameterized N 0 as a function of temperature and snow mixing ratio. Variable snow intercept parameter: An empirical parameterization

5. QUEST-Meeting, 14. Dez. 2007, Offenbach 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 N 0,s (T).

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

7. QUEST-Meeting, 14. Dez. 2007, Offenbach 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.

8. QUEST-Meeting, 14. Dez. 2007, Offenbach 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).

9. QUEST-Meeting, 14. Dez. 2007, Offenbach IWC validation with cloud radar 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. Operational COSMO-EU LMQ Experiment

10. QUEST-Meeting, 14. Dez. 2007, Offenbach IWC validation with cloud radar 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. LMQ new microphysics LMQ old microphysics

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

12. QUEST-Meeting, 14. Dez. 2007, Offenbach IWC validation with cloud radar 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. LMQ new microphysics LMQ old microphysics