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The new multilayer land surface scheme TERRA-ML

The new multilayer land surface scheme TERRA-ML. Validation and improvement with the Rhone-AGG dataset. M. Lange, Bodo Ritter, German Weather Service DWD email: martin.lange@dwd.de. Outline. The Rhone-Agg experiment Soil model TERRA-ML Setup for the validation experiment

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The new multilayer land surface scheme TERRA-ML

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  1. The new multilayer land surface scheme TERRA-ML Validation and improvement with the Rhone-AGG dataset M. Lange, Bodo Ritter, German Weather Service DWD email: martin.lange@dwd.de

  2. Outline • The Rhone-Agg experiment • Soil model TERRA-ML • Setup for the validation experiment • Model results TERRA-ML vs. others • Summary and outlook

  3. Rhone-Agg experiment www.cnrm.meteo.fr/mc2/projects/rhoneagg/index.html Validation domain

  4. Physics of TERRA-ML

  5. Physics of TERRA-ML

  6. Experimental setup • Run of soil model as stand alone scheme with external atmospheric forcing and prescribed soil and vegetation parameter. • 4 years period 1.08.1985 -31.07.1989, 1 year spin up, 3 years validation • Initialisation of soil moisture with July 89 results from prerun.

  7. Model input data: 3 hour atmospheric forcing parameter from SAFRAN model

  8. Model input data: Soil properties

  9. Results Results from TERRA-ML are discussed as area averaged monthly mean values for the validation period (Aug. 1986 - July 1989) and compared with model results from ISBA (CNRM), ECMWF and NOAA. • 4 different runs are presented • 1. initial test run • 2. adjusted transpiration from vegetation • 3. Snow aging by decrease of albedo • 4. Snow melting from upper side • Summary of different runs for TERRA-ML

  10. TERRA-ML initial test run TERRA-ML ECMWF NOAH ISBA

  11. TERRA-ML initial test run TERRA-ML ECMWF NOAH ISBA

  12. Conclusion from 1st run • Total evapotranspiration is much lower than in other models. This is due to a bug in transpiration from vegetation. • bare soil evaporation too large • soil moisture too large • 3D snow water equivalent increases • accumulates continuously, snow does not melt at high altitude gridpoints during summer

  13. 2nd Run: adjusted transpiration from vegetation • Model physics has been reviewed and transpiration from vegetation has been corrected (R. Schrodin).

  14. Adjusted transpiration from vegetation TERRA-ML ECMWF NOAH ISBA

  15. Adjusted transpiration from vegetation TERRA-ML ECMWF NOAH ISBA

  16. Adjusted transpiration from vegetation TERRA-ML ECMWF NOAH ISBA

  17. Adjusted transpiration from vegetation TERRA-ML ECMWF NOAH ISBA

  18. Conclusion from 2nd run • Evaporation components adjust according to correct transpiration from vegetation • Bare soil evaporation decreases • Total evapotranspiration and corresponding latent heat flux fit to other model results, • During summer latent heat flux slightly stronger, sensible heat flux weaker • Soil moisture is at the lower edge of different models, variation is similar • Stronger transpiration dehumidifies the Soil • 3D snow water equivalent still too large • Change could not be expected from modification of TVeg

  19. 3rd run: Aging of snow • Snow melting is too weak • resulting from slow heating of thick snow layer • Aging of snow leads to decrease of albedo. Enhanced absorption of solar radiation increase snow melting during summer. • New process with continuous variation of snow albedo between maximum of 0.7 for fresh snow and minimum of 0.4 for old snow (B. Ritter). • Fresh snow is given after snowfall of 5 mm snow water equivalent within less than one day. • Old snow is given after one week without snowfall.

  20. Decrease of albedo by aging of snow TERRA-ML ECMWF NOAH ISBA

  21. Decrease of albedo by aging of snow TERRA-ML ECMWF NOAH ISBA

  22. Decrease of albedo by aging of snow TERRA-ML ECMWF NOAH ISBA

  23. Conclusion from 3rd run • Evaporation and soil water components do not change significantly. • Runoff does not change strongly although snow melting increases during summer. • Increased snow melting from aging of snow corrects accumulation of snow. • At some high altitude gridpoints snow does not vanish totally in summer. Minimum snow albedo of 0.2 improves the result but is not realistic.

  24. 4th Run: Snow melting from top side • In previous simulations snow was melted from the bottom side in the sense that no melting occurred before the top soil layer was heated up to Tmelt. • In fact melting especially of glaciers occurs in far the most cases from the top side due to solar radiation or liquid precipitation. • Therefore snow melting from the top side is included (B. Ritter, E. Heise), i.e. for the case that average snow temperature exceeds Tmelt and the temperature of top soil layer is below Tmelt.

  25. Melting of snow from the top side TERRA-ML ECMWF NOAH ISBA

  26. Conclusion from 4th run • Snow water equivalent does not change significantly, snow accumulation increases slightly. • Evaporation and soil water components do not change significantly • Surface runoff increases, sub surface runoff decreases during summer. • Melted snow contributes directly to surface runoff. In earlier version surface runoff required saturation of top soil level up to field capacity.

  27. Comparison of TERRA-ML simulations TVEG KORR AGING SNOW MELTING TOP SIDE 1. RUN

  28. Comparison of TERRA-ML simulations TVEG KORR AGING SNOW MELTING TOP SIDE 1. RUN

  29. Comparison of TERRA-ML simulations TVEG KORR AGING SNOW MELTING TOP SIDE 1. RUN

  30. Comparison of TERRA-ML simulations TVEG KORR AGING SNOW MELTING TOP SIDE 1. RUN

  31. Summary • The Rhone-Agg dataset has been proved as a powerfull tool for validation and improvement of TERRA-ML. • The different simulations have discovered a bug in calculation of transpiration rate and deficiencies in the physical parameterization of snow melting at high altitude regions during summer. • Problems have been fixed, some accumulation of snow still occurs. • In a 1 layer snow scheme melting is slowly for deep snow since average temperature of the whole snowpack must exceed Tmelt.

  32. Summary • TERRA-ML is a modern state of the art multilayer LSS that compares with its main results to other prominent LSS. • It has to be kept in mind that all results are „model results“ and for most components it is not clear what the „best“ result is. • The comparison of river discharge calculated from the hydrological routing model MODCOU with observations is a part of CNRM work. • Presented?

  33. Future tasks • Eldas project is designed to develop a land data assimilation system. Soil moisture is optimized with respect to • 2m screen level temperature (1D Var data assimilation Hess, 2001) • 2m relative humidity • surface radiation (Uni Bonn)

  34. Acknowledgement • Piedro Viterbo from ECMWF Aaron Boone from CNRM and Dag Lohmann from NOAA center to show their model results. • Special thanks to Aaron Boone at CNRM who coordinates the Rhone-Agg experiment in the group of Joel Noilhan, and provided the results from different participants in the Rhone-Agg Experiment. • Physics section at DWD worked very efficiently to eliminate deficiencies.

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