1. Slide 1 PA Surface II of IV - training course 2006 Slide 1 Introduction General remarks Model development and validation The surface energy budget Soil heat transfer Soil water transfer Surface water fluxes Initial conditions Snow Conclusions and a look ahead Layout

2. Slide 2 PA Surface II of IV - training course 2006 Slide 2 Thermal budget of a ground layer at the surface G D H LE Day Night

3. Slide 3 PA Surface II of IV - training course 2006 Slide 3 Energy budget: Summer examples Dry Barley field Fir canopy Arya, 1988

4. Slide 4 PA Surface II of IV - training course 2006 Slide 4 The surface radiation In some cases (snow, sea ice, dense canopies) the impinging solar radiations penetrates the “ground” layer and is absorbed at a variable depth. In those cases, an extinction coefficient is needed. Surface albedo Surface emissivity Skin temperature Arya, 1988

5. Slide 5 PA Surface II of IV - training course 2006 Slide 5 The other terms Evaporation Sensible heat flux specify the surface Ground heat flux

6. Slide 6 PA Surface II of IV - training course 2006 Slide 6 Recap: The surface energy equation Equation for For: - a thin soil layer at the top -G (T s,T sk ) is known, or parameterized or G << R n we have a non-linear equation defining the skin temperature

7. Slide 7 PA Surface II of IV - training course 2006 Slide 7 Skin layer at the interface between soil (snow) and atmosphere; no thermal inertia, instantaneous energy balance At the interface soil/atmosphere, each grid-box is divided into fractions (tiles), each fraction with a different functional behaviour. The different tiles see the same atmospheric column above and the same soil column below. If there are N tiles, there will be N fluxes, N skin temperatures per grid-box There are currently up to 6 tiles over land (N=6) TESSEL

8. Slide 8 PA Surface II of IV - training course 2006 Slide 8 TESSEL skin temperature equation Grid-box quantities

9. Slide 9 PA Surface II of IV - training course 2006 Slide 9 Tiles Interception layer Bare ground Snow on low vegetation High vegetation with snow beneath Sea ice / frozen lakesLow vegetation Open sea / unfrozen lakesHigh vegetation Sea and iceLand

10. Slide 10 PA Surface II of IV - training course 2006 Slide 10 TESSEL geographic characteristics Annual, Dependent on vegetation type 1 m Global constant Root depth Root profile Annual, Dependent on vegetation type Global constants LAI r smin MonthlyAnnualAlbedo Dominant low type Dominant high type Global constant (grass) Vegetation type Fraction of low Fraction of high FractionVegetation TESSELERA15Fields

11. Slide 11 PA Surface II of IV - training course 2006 Slide 11 High vegetation fraction at T511 ( now at T799 ) Aggregated from GLCC 1km

12. Slide 12 PA Surface II of IV - training course 2006 Slide 12 Low vegetation fraction at T511 ( now at T799 ) Aggregated from GLCC 1km

13. Slide 13 PA Surface II of IV - training course 2006 Slide 13 High vegetation type at T511 ( now at T799 ) Aggregated from GLCC 1km

14. Slide 14 PA Surface II of IV - training course 2006 Slide 14 Low vegetation type at T511 ( now at T799 ) Aggregated from GLCC 1km

15. Slide 15 PA Surface II of IV - training course 2006 Slide 15 Introduction General remarks Model development and validation The surface energy budget Soil heat transfer Soil water transfer Surface water fluxes Initial conditions Snow Conclusions and a look ahead Layout

16. Slide 16 PA Surface II of IV - training course 2006 Slide 16 Soil science miscellany (1) The soil is a 3-phase system, consisting of -minerals and organic mattersoil matrix -watercondensate (liquid/solid) phase -moist air trappedgaseous phase Texture - the size distribution of soil particles Hillel 1982, 1998

17. Slide 17 PA Surface II of IV - training course 2006 Slide 17 Soil science miscellany (2) Structure - The spatial organization of the soil particles Porosity - (volume of maximum air trapped)/(total volume) Composition Water content Hillel 1982,1998 Reference: Hillel 1998 Environmental Soil Physics, Academic Press Ed.

18. Slide 18 PA Surface II of IV - training course 2006 Slide 18 Soil properties Rosenberg et al 1983 Arya 1988

19. Slide 19 PA Surface II of IV - training course 2006 Slide 19 Ground heat flux In the absence of phase changes, heat conduction in the soil obeys a Fourier law Boundary conditions: TopNet surface heat flux BottomNo heat flux OR prescribed climate

20. Slide 20 PA Surface II of IV - training course 2006 Slide 20 Diurnal cycle of soil temperature summer winter bare sod Rosenberg et al 1983 50 cm depth surface summer

21. Slide 21 PA Surface II of IV - training course 2006 Slide 21 TESSEL Solution of heat transfer equation with the soil discretized in 4 layers, depths 7, 21, 72, and 189 cm. No-flux bottom boundary condition Heat conductivity dependent on soil water Thermal effects of soil water phase change ↓ 10.6 ~ 55.8 d ↓0.1~0.6 d ↓ 1.1~5.8 d Time-scale for downward heat transfers in wet/dry soil

22. Slide 22 PA Surface II of IV - training course 2006 Slide 22 TESSEL soil energy equations DjDj TjTj j-1 j+1 G j+1/2 G j-1/2

23. Slide 23 PA Surface II of IV - training course 2006 Slide 23 Case study: winter (1) Model vs observations, Cabauw, The Netherlands, 2 nd half of November 1994 Soil 140 m 2 m

24. Slide 24 PA Surface II of IV - training course 2006 Slide 24 Case study: winter (2) Soil Temperature, North Germany, Feb 1996: Model (28-100 cm) vs OBS 50 cm Observations: Numbers Model: Contour

25. Slide 25 PA Surface II of IV - training course 2006 Slide 25 Model bias: -Net radiation (Rnet) too large -Sensible heat (H) too small  But (Tair-Tsk) too large (too large diurnal cycle)  Therefore f(Ri) problem -Soil does not freeze (soil temperature drops too quickly seasonally) Case study: winter (3) T air T skin Rnet H LE G Stability functions Soil water freezing Viterbo, Beljaars, Mahfouf, and Teixeira, 1999: Q.J. Roy. Met. Soc., 125,2401-2426.

26. Slide 26 PA Surface II of IV - training course 2006 Slide 26 Winter: Soil water freezing Soil heat transfer equation in soil freezing condition Apparent heat capacity

27. Slide 27 PA Surface II of IV - training course 2006 Slide 27 Case study: winter (4) 1 Oct 1 Jan 1 Dec 1 Nov 1 Feb Germany soil temperature: Observations vs Long model relaxation integrations Observations Control Stability Stab+Freezing

28. Slide 28 PA Surface II of IV - training course 2006 Slide 28 Northern Hemisphere Case study: winter (5) Soil water freezing acts as a thermal regulator in winter, creating a large thermal inertia around 0 C. Simulations with soil water freezing have a near-surface air temperature 5 to 8 K larger than control. In winter, stable, situations the atmosphere is decoupled from the surface: large variations in surface temperature affect only the lowest hundred metres and do NOT have a significant impact on the atmosphere. Europe 850 hPa T RMS forecast errors Stab+freezing Control

29. Slide 29 PA Surface II of IV - training course 2006 Slide 29 Introduction General remarks Model development and validation The surface energy budget Soil heat transfer Soil water transfer Surface water fluxes Initial conditions Snow Conclusions and a look ahead Layout

30. Slide 30 PA Surface II of IV - training course 2006 Slide 30 More soil science miscellany 3 numbers defining soil water properties -Saturation (soil porosity)Maximum amount of water that the soil can hold when all pores are filled0.472 m 3 m -3 -Field capacity“Maximum amount of water an entire column of soil can hold against gravity”0.323 m 3 m -3 -Permanent wilting pointLimiting value below which the plant system cannot extract any water0.171 m 3 m -3 Hillel 1982 Jacquemin and Noilhan 1990

31. Slide 31 PA Surface II of IV - training course 2006 Slide 31 Schematics Hillel 1982 Root extraction The amount of water transported from the root system up to the stomata (due to the difference in the osmotic pressure) and then available for transpiration Boundary conditions: TopSee later BottomFree drainage or bed rock

32. Slide 32 PA Surface II of IV - training course 2006 Slide 32 Soil water flux Darcy’s law > 3 orders of magnitude > 6 orders of magnitude Mahrt and Pan 1984

33. Slide 33 PA Surface II of IV - training course 2006 Slide 33 TESSEL: soil water budget Solution of Richards equation on the same grid as for energy Clapp and Hornberger (1978) diffusivity and conductivity dependent on soil liquid water Free drainage bottom boundary condition Surface runoff, but no subgrid-scale variability; It is based on infiltration limit at the top One soil type for the whole globe: “loam”

34. Slide 34 PA Surface II of IV - training course 2006 Slide 34 TESSEL soil water equations (1) DjDj j-1 j+1 F j+1/2 F j-1/2 ↓ 11.7 ~ >> d ↓0.1~19.7 d ↓ 1.2~195.9 d Time-scale for downward water transfers in wet/dry soil

35. Slide 35 PA Surface II of IV - training course 2006 Slide 35 TESSEL soil water equations (2)

36. Slide 36 PA Surface II of IV - training course 2006 Slide 36 TESSEL geographic characteristics Annual, Dependent on vegetation type 1 m Global constant Root depth Root profile Annual, Dependent on vegetation type Global constants LAI r smin MonthlyAnnualAlbedo Dominant low type Dominant high type Global constant (grass) Vegetation type Fraction of low Fraction of high FractionVegetation TESSELERA15Fields

37. Slide 37 PA Surface II of IV - training course 2006 Slide 37 FIFE: Time evolution of soil moisture Viterbo and Beljaars 1995 pwp cap Time pwp cap 156 167 184 177 217 213 191 226 231 247 257 268 276 285 June July August September October