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Layout. Introduction General remarks Model development and validation The surface energy budget The surface water budget Soil heat transfer Soil water transfer Snow Initial conditions Conclusions and a look ahead. H. LE. Day. D. Night. G.

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  1. PA Surface II of IV - training course 2010 Layout • Introduction • General remarks • Model development and validation • The surface energy budget • The surface water budget • Soil heat transfer • Soil water transfer • Snow • Initial conditions • Conclusions and a look ahead

  2. PA Surface II of IV - training course 2009 H LE Day D Night G Thermal budget of a ground layer at the surface

  3. PA Surface II of IV - training course 2009 Dry Fir canopy Barley field Energy budget: Summer examples Arya, 1988

  4. PA Surface II of IV - training course 2009 Surface albedo Surface emissivity Skin temperature 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. Arya, 1988

  5. PA Surface II of IV - training course 2009 Sensible heat flux specify the surface Evaporation Ground heat flux The other terms

  6. PA Surface II of IV - training course 2009 Recap: The surface energy equation • Equation for • For: • a thin soil layer at the top • G (Ts,Tsk) is known, or parameterized or G << Rn we have a non-linear equation defining the skin temperature

  7. PA Surface II of IV - training course 2009 Land Sea and ice High vegetation Open sea / unfrozen lakes Low vegetation Sea ice / frozen lakes High vegetation with snow beneath Snow on low vegetation Bare ground Interception layer Tiles

  8. PA Surface II of IV - training course 2009 Fields ERA15 TESSEL Vegetation Fraction Fraction of low Fraction of high Vegetation type Global constant (grass)‏ Dominant low type Dominant high type Albedo Annual Monthly LAI rsmin Global constants Annual, Dependent on vegetation type Root depth Root profile 1 m Global constant Annual, Dependent on vegetation type TESSEL geographic characteristics

  9. PA Surface II of IV - training course 2009 High vegetation fraction at T511 (now at T799)‏ Aggregated from GLCC 1km

  10. PA Surface II of IV - training course 2009 Low vegetation fraction at T511 (now at T799)‏ Aggregated from GLCC 1km

  11. PA Surface II of IV - training course 2009 High vegetation type at T511 (now at T799)‏ Aggregated from GLCC 1km

  12. PA Surface II of IV - training course 2009 Low vegetation type at T511 (now at T799)‏ Aggregated from GLCC 1km

  13. PA Surface II of IV - training course 2009 Layout • Introduction • General remarks • Model development and validation • The surface energy budget • The surface water budget • Soil heat transfer • Soil water transfer • Snow • Initial conditions • Conclusions and a look ahead

  14. PA Surface II of IV - training course 2009 Snow Lake Dry vegetation Wet vegetation Bare ground Evaporation: Idealized surfaces

  15. PA Surface II of IV - training course 2009 • Evaporation efficiency • Ratio of evaporation to potential evaporation • Bucket model Budyko 1963, 1974 Manabe 1969 1 0 Potential evaporation, bucket model • Potential evaporation • The evaporation of a large uniform surface, sufficiently moist or wet (the air in contact to it is fully saturated)‏

  16. PA Surface II of IV - training course 2009 A general, algebraic formulation • Two limit behaviours • Bare soil: Evaporation dependent on soil water (and trapped water vapor) in a top shallow layer of soil (~ 20 mm). • Vegetated surfaces: Evaporation controlled by a canopy resistance, dependent on shortwave radiation, water on the root zone (~ 1-5 m deep) and other physical/physiological effects.

  17. PA Surface II of IV - training course 2009 Transpiration: The big leaf approximation • Sensible heat (H), the resistance formulation • Evaporation (E), the resistance formulation (the big leaf approximation, Deardorff 1978, Monteith 1965)‏

  18. PA Surface II of IV - training course 2009 Some plant science • rs, the stomatal resistance of a single leaf. Physiological control of water loss by the vegetation. Stomata (valve-like openings) regulate the outflow of water vapour (assumed to be saturated in the stomata cells) and the intake of CO2 from photosynthesis. The energy required for the opening is provided by radiation (Photosynthetically Active Radiation, PAR). In many environments the system appears to be operate in such a way to maximize the CO2 intake for a minimum water vapour loss. When soil moisture is scarce the stomatal apertures close to prevent wilt and dessication of the plant.

  19. PA Surface II of IV - training course 2009 Jarvis approach(1)‏ Dickinson et al 1991

  20. PA Surface II of IV - training course 2009 Jarvis approach(2)‏ Shuttleworth 1993

  21. PA Surface II of IV - training course 2009 Bare ground evaporation • Soil (bare ground) evaporation is due to: • Molecular diffusion from the water in the pores of the soil matrix up to the interface soil atmosphere (z0q)‏ • Laminar and turbulent diffusion in the air between z0q and screen level height • All methods are sensitive to the water in the first few cm of the soil (where the water vapour gradient is large). In very dry conditions, water vapour inside the soil becomes dominant

  22. PA Surface II of IV - training course 2009 TESSEL transpiration

  23. PA Surface II of IV - training course 2009 TESSEL root profile

  24. PA Surface II of IV - training course 2009 TESSEL evaporation: shaded snow • Evaporation is the sum of the contribution of the snow underneath (with an additional resistance, ra,s ,to simulate the lower within canopy wind speed) and the exposed canopy. The former is dominant in early spring (frozen soils) and the latter is dominant in late spring.

  25. PA Surface II of IV - training course 2009 TESSEL bare ground evaporation

  26. PA Surface II of IV - training course 2009 Land Sea and ice High vegetation Open sea / unfrozen lakes Low vegetation Sea ice / frozen lakes High vegetation with snow beneath Snow on low vegetation Bare ground Interception layer Tiles

  27. PA Surface II of IV - training course 2009 Interception (1)‏ • Interception layer represents the water collected by interception of precipitation and dew deposition on the canopy leaves (and stems) • Interception (I) is the amount of precipitation (P) collected by the interception layer and available for “direct” (potential) evaporation. I/P ranges over 0.15-0.30 in the tropics and 0.25-0.50 in mid-latitudes. • Leaf Area Index (LAI) is (projected area of leaf surface)/(surface area) 0.1 < LAI < 6 • Two issues • Size of the reservoir • Cl, fraction of a gridbox covered by the interception layer • T=P-I; Throughfall (T) is precipitation minus interception

  28. PA Surface II of IV - training course 2009 Interception: Canopy water budget

  29. PA Surface II of IV - training course 2009 TESSEL: interception • Interception layer for rainfall and dew deposition

  30. PA Surface II of IV - training course 2009 Example: Deep tropics interception ARME, 1983-1985, Amazon forest Accumulated water fluxes Interception Evaporation Interception Viterbo and Beljaars 1995

  31. PA Surface II of IV - training course 2009 Case study: Aerodynamic resistance (1)‏ • Cabauw (Netherlands), is a grass covered area, where multi-year detailed boundary layer measurements have been taken • Observations were used to force a stand-alone version of the surface model for 1987 • The first model configuration tried had z0h=z0m

  32. PA Surface II of IV - training course 2009 Case study: Aerodynamic resistance (2)‏ Beljaars and Viterbo 1994

  33. PA Surface II of IV - training course 2009 Case study: Aerodynamic resistance (3)‏

  34. PA Surface II of IV - training course 2009 Case study: Aerodynamic resistance (4)‏

  35. PA Surface II of IV - training course 2009 Case study: Aerodynamic resistance (5)‏

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