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The new multi-layer snow model

The new multi-layer snow model. Guy de Morsier 1 , Jean-Marie Bettems 1 , Ekaterina Machulskaya 2 1 MeteoSwiss 2 DWD COSMO General Meeting Offenbach, 7 September 2009. Overview. Update of the multi-layer snow model Available data for validations Validation experiments

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The new multi-layer snow model

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  1. The new multi-layer snow model Guy de Morsier1, Jean-Marie Bettems1,Ekaterina Machulskaya2 1MeteoSwiss 2DWD COSMO General Meeting Offenbach, 7 September 2009

  2. Overview • Update of the multi-layer snow model • Available data for validations • Validation experiments • Results from the 2 layer snow model • Conclusions • Outlook

  3. Update of the multi-layer snow model • Now in COSMO 4.7 • new fields with ke_snow levels T_SNOW_M mean temperature of the snow layer (K) DH_SNOW_M layer thickness between interfaces (m) WL_SNOW_M liquid water content in the snow (m H2O) WT_SNOW_M total (liquid+solid) water content (m H2O) • GRIB details checked with Uli Schättler • Start mechanisms: • laf* files read and write all necessary variables • re-start files continue computing snow model • cold-start initialise snow variables from old 1 layer model • Additional CPU cost: less than 1% for 2 layers • Scientific documentation available • Technical documentation: • description of new fields • switches, namelists • tuning parameters

  4. Available data for validation (i) • MSG quality weighted snow mask onCOSMO-7 and COSMO-2 grid • IMIS measurement at ca. 90 Swiss stations between 1800 and 3000mAMSL from WSL Institute for Snow and Avalanche Research, SLF http://www.slf.ch/lawineninfo/zusatzinfos/Archiv/index_EN. • SLF snow height analysis using all IMIS/ENET & NOAA data. • Operational snow analysis: COSMO-7, COSMO-2 • SNOWPACK finite element model of layered snow structures (including phase change, water transport and snow drifting) at7 Swiss stations.

  5. Available data for validation (ii) Re-grided with “fieldextra”: SLF analysis: original 1km resolution

  6. Validation experiments • Winter from September 2007 to May 2008 • COSMO-7 results are from the operational data assimilation including a daily merge of the snow analysis • snowanalysis uses surface observations and the snow mask derived from Meteosat Second Generation SEVIRI (temporal composite) • ReferenceTERRA stand-alone (COSMO SVAT with a single snow layer) driven by hourly atmospheric analysis including precipitation for the whole period without snow analysis • New snow modelSame as reference but with 2 layer snow model (2LSM)

  7. Validation experiments • Spurious precipitation at lateral boundary (qi in IFS, lmixcld=.F.) Time series of domain mean [m] for 2LSM,COSMO-7 and REF Bias= 2LSM - REF [m] REF is TERRA stand-alone without snow analysis. • REF has less snow than COSMO-7 • 2LSMhas more snow on the orography

  8. Percent Correct Classification (MSG) 6.6km PCC (hits + correct neg.) C-7 PCC (hits + correct neg.) REF hits=4% fa=0.0% cn=96% mis=0% hits=3.4% fa=2.8% cn=93.2% mis=0.6% MSG Quality Mask SNOW present PCC (hits + correct neg.) 2LSM hits=3.4% fa=2.4% cn=93.6% mis=0.6%

  9. Compare with SLF and MSG data at 6.6km PCC(hits+cor.neg.) SLF PCC(hits+cor.neg.)REF hits=54.7% fa=41.9% cn=3.4% mis=0% hits=41.4% fa=8.8% cn=46.7% mis=3.1% PCC(hits+cor.neg.)2LSM MSG Quality Mask SNOW analysed by SLF: 36 cases hits=41.4% fa=7.9% cn=47.1% mis=3.6%

  10. Validation with SLF data at 6.6km Bias (COSMO-7 – SLF) [m] Bias(REF – SLF) [m] Bias(2LSM – SLF) [m] • Period:September 8, 2007 to May 31, 2008 • COSMO-7only 35 cases. • REF& 2LSMonly 36 cases. • REF has too little snow • 2LSM has too much snow

  11. Obs! : OKPeriod: September 2, 2007 to May 31, 2008 : + : -EVERY day : |Dh|>300m Results with 2 layer snow model (2LSM) Bias(2LSM – SLF) [m] ZOOM _ SNOWPACK stations

  12. Results with 2 layer snow model (2LSM) Station at 2240min the Western Alps Model at 2097m Dh = -143m OKPeriod: September 2, 2007 to May 31, 2008 EVERY day

  13. Results with 2 layer snow model (2LSM) Station at 1510mon the NorthWestern slope of theAlps Model at1462m Dh = -48m Too little!Period: September 2, 2007 to May 31, 2008 EVERY day

  14. Results with 2 layer snow model (2LSM) Station at 1650mon the NorthWestern slope of theAlps Model at1654m Dh = 4m Too little but Period: September 2, 2007 to May 31, 2008 good ablationEVERY day

  15. Results with 2 layer snow model (2LSM) Station at 2230m Next grid point South Model at2177m Dh = -53m OKPeriod: September 2, 2007 to May 31, 2008 EVERY day

  16. Results with 2 layer snow model (2LSM) Bias(2LSM – SLF) [m] ZOOM _ SNOWPACK stations Obs! : OKPeriod: September 2, 2007 to May 31, 2008 : + : -EVERY day : |Dh|<300m

  17. Results with 2 layer snow model (2LSM) Station at 2430m In the Alps Model at2479m Dh = 49m Too muchPeriod: September 2, 2007 to May 31, 2008

  18. Results with 2 layer snow model (2LSM) Station at 2450m 2 grid points to the East Model at2350m Dh = -100m OKPeriod: September 2, 2007 to May 31, 2008

  19. Results with 2 layer snow model (2LSM) • Station at 2195m • Within the Alps • Model at2192m • Dh = -3m • dubious observations! • possiblewind ablation Obs!Period: September 2, 2007 to May 31, 2008

  20. Results with 2 layer snow model (2LSM) Height difference 9m -47m Northslope of the Alps 2 neighbor grid points: North South • dubious observations? • or possibleaccumulation SNOWPACK Period: September 2, 2007 to May 31, 2008 stations!

  21. Results with 2 layer snow model (2LSM) • Station at 1340m • Northslope of theAlps • Model at1331m • Dh = -9m • Problem when merging the analysis (red) with the new model OK but… Period: September 2, 2007 to May 31, 2008

  22. Conclusions • Slightly better snow/no snow with multi layer snow model over Northern Europe • In Eastern Europe and over orography the new snow model produces larger snow depth • The systematic underestimation of the snow height by the original snow model is largely removed by using the2 layer snow model • The multi layer snow model works well at different altitudesin complex topographybut might overestimate the snow height in some areas Findings: • better representation of the ablation period (Spring) with the 2 layer snow model

  23. Outlook • Snow model: • check other snow model variables (SNOWPACK):snow water content (liquid and total), snow temperature • look at wet and dry periods and spatial distribution of precip. • evaluate temporal evolution also outside of the Alps • re-compute winter 2007-2008 with full 3D model with COSMO-7 and COSMO-2 • in particular evaluate effect of higher resolution • Snow analysis: • Adapt to better use the good informationprovided by the new snow model

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