Changes between Version 19 and Version 20 of doc/tec/lsm

Timestamp:

Apr 5, 2016 8:15:32 AM (9 years ago)

Author:

maronga

Comment:

--

doc/tec/lsm

@@ -105 +105 @@
 
 == Soil model ==
-The soil model consists of prognostic equations for the soil temperature and the volumetric soil moisture which are solved for multiple layers. The soil model only takes into account vertical transport within the soil and no ice phase is considered. By default, the soil model consists of four layers, in which the vertical heat and water transport is modelled using the Fourier law of diffusion and Richards' equation, respectively. Also, root fractions can be assigned to each soil layer to account for the explicit water withdrawal of plants used for transpiration from the respective soil layer. 
+The soil model consists of prognostic equations for the soil temperature and the volumetric soil moisture which are solved for multiple layers. The soil model only takes into account vertical transport within the soil and no ice phase is considered. By default, the soil model consists of four layers (see figure below), in which the vertical heat and water transport is modelled using the Fourier law of diffusion and Richards' equation, respectively. Also, root fractions can be assigned to each soil layer to account for the explicit water withdrawal of plants used for transpiration from the respective soil layer. 
 [[Image(lsm_simple.png,300px)]]
 
@@ -200 +200 @@
 {{{
 #!Latex
+$alpha$: Van Genuchten coefficient\\
 $h$: Pressure head\\
 $n$: Van Genuchten coefficient\\
@@ -218 +219 @@
 \end{equation}
 }}}
+
+=== Root extraction ===
+The root extraction of water from the respective soil layer ''S,,m,,'' is calculated as follows:
+{{{
+#!Latex
+\begin{equation*}
+m_total = \sum \limits_{k = 0}^3 R_\mathrm{fr}(k) * m_soil(k)
+\end{equation*}
+}}}
+where ''m'',,total,, is the total water content of the soil. Only those layer are summed up which have a soil moisture above wilting point (plants do not extract water from such layers). The root extraction is then given by
+{{{
+#!Latex
+\begin{equation*}
+S_m = \dfrac{LE_\mathrm{veg}}{rho_l\ l_v} \sum \limits_{k = 0}^3 R_\mathrm{fr}(k) * \dfrac{m_soil(k)}{m_total(k)} 
+\end{equation*}
+}}}
+Again, only layers where the soil moisture is above its value at wilting point are used for root extraction (which is zero otherwise).
+
+
+=== Boundary conditions ===
+Neumann boundary conditions are used for the transport of heat and moisture at the upper boundary (surface). The values are given by the energy balance in terms of ''G'' for heat and ''LE'',,soil,,, for moisture. At the bottom boundary a deep soil temperature is prescribed (Dirichlet conditions), whereas two options are available for soil moisture. The underlying surface can be set to either bedrock (no moisture flux at the bottom, water conserving) or to open bottom (implies non-conservation of water). 
+
 
 For more details, see also [#viterbo Viterbo et al. (1995)] and [#balsamo Balsamo et al. (2009)].