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Evaporation processes, heat and mass transfer in atmosphere and soil

Evaporation processes, heat and mass transfer in atmosphere and soil. Per-Erik Jansson. What are the reasons for evaporation ?. Energy Transport of water and heat in the atmosphere Transport of water and heat in the soil. What are the principles of importance for understanding Evaporation ?.

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Evaporation processes, heat and mass transfer in atmosphere and soil

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  1. Evaporation processes, heat and mass transfer in atmosphere and soil Per-Erik Jansson

  2. What are the reasons for evaporation ? • Energy • Transport of water and heat in the atmosphere • Transport of water and heat in the soil

  3. What are the principles of importance for understanding Evaporation ? • Conservation of energy • Conservation of mass • Termodynamics, second low

  4. What are the major uncertainties ? • Vertical transport properties both in soil and atmosphere • Horizontal transport of heat in the amosphere, local advection • Feed back between the soil and the atmosphere.

  5. Various types of methods • Mechanistic methods that is based on all the major principles • Simplified empirical methods that are based on the most important factors

  6. Mechanistic based Method Energy balance approach

  7. Surface energy balance • The land surface on average is heated by net radiation balanced by the latent and sensible heat flow to atmosphere and heat flow to the soil. + = +

  8. Net Radiation Symbols in the equations that represent important parameters in the CoupModel are indicated. In some cases the symbols are expanded to function, i.e. representing more parameters to estimate the value of the symbol. All Symbols are explained in detail in the CoupModel help or in the official documentation on the web.

  9. Average net shortwave radiation at the Earth's surface: January 1984-1991. Color range: blue - red - white, Values: 0 to 350 W/m2. Global mean = 162 W/m2, Minimum = 0 W/m2, Maximum = 315 W/m2. (Source: NASA Surface Radiation Budget Project).

  10. Heat flow in atmosphere Atmosphere SOIL

  11. Aerodynamic Resistance

  12. The aerodynamic resistance decreases with increasing wind speed. The plot shows the effect on resistance of different roughness lengths, z0M: blue = 0.001, green = 0.005).

  13. Soil Heat Flow • Heat flow in the soil is the sum of conduction, the first term, and convection, the last two terms: • where the indices h, v and w mean heat, vapour and liquid water, qis flux, k is conductivity, T is soil temperature, C is heat capacity, L is latent heat and z is depth. The first convective term, CwTqw, may or may not be included in the solution depending on the switch “Convection flow”. Normally this convective term is important at high flow rates e.g. during heavy snow melt infiltration. The other convective term, the latent heat flow by water vapour, Lvqv, is also optional (see switch “Vapour flow”).

  14. Vapour flow in soil

  15. Water flow in soil (liquid)

  16. Vapour pressure at the soil surface [

  17. Moisture availability at soil surface The relative humidity at the soil surface as a function of the pressure head in the upper soil layer after correction for non equilibrium conditions.

  18. Semi EmpiricalMethod Penman Monteith equation

  19. Empirical approach

  20. The two different empirical functions for soil surface resistance PsiRs3pf1 = 1, PsiRs 3pf2 = 300, PsiRs 3pf3 = 100. PsiRs1p = 200.

  21. Summary • The partitioning of energy at the soil or land surface is the major engine in the climate systems • The partitioning depends on many factors but most important is the availability of water • The availability of water is strongly controlled by processes that are affected by management • The role of management for the control of water resources is a very important component also in the climate system • Various models may be useful to increase our understanding and being a base for design of improved water management • A system that includes vegetation is more complex but the principles for partioning of energy are similar

  22. Hint for Simulation Tutorial • Combine the reading of the instruction for the tutorial with present material. • Look more into the theory by searching for literature on the web. IPCC have many e-books available that gives another spatial scale to the same basic phenomena. • Try to understand major advantages of various methods for evaporation estimation. • Try to understand major differences to typical evaporation estimation in conceptual rainfall-runoff models.

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