Changes between Version 4 and Version 5 of palm4u

Timestamp:

Dec 12, 2017 3:35:58 PM (7 years ago)

Author:

maronga

Comment:

--

palm4u

@@ -7 +7 @@
 In the following an overview of the PALM-4U components is given. Note that some of these still undergo major changes and improvements at the moment. A final documentation and publications are planned in 2018 and 2019.
 
-== Building parameterization ==
+== Topography parameterization ==
 The Cartesian topography in PALM is generally based on the mask method ([#briscolini1989 Briscolini and Santangelo, 1989]) and allows for explicitly resolving solid obstacles such as buildings and orography. The implementation makes use of the following simplifications:
 
@@ -32 +32 @@
 
 Simulations with topography require the application of MOST between each surface and the first computational grid point outside of the topography. 
-For vertical and horizontal downward-facing surfaces, neutral stratification is assumed for MOST, even if MOST is strictly speaking derived only for upward-facing horizontal surfaces. This is simply attributed to the lack of knowledge in the literature about the best practice in this matter. \\\\
+For vertical and horizontal downward-facing surfaces, neutral stratification is assumed for MOST.
 
-Missing:
-* Coupling to LSM and USM
-* Terrain height and topography
+In the PALM core, buildings are primarily realized as obstacles that react to the flow dynamics via form drag
+and friction forces by assuming a constant flux layer between the building surface and the adjacent air volume. A simple thermodynamic coupling is also possible by prescribing surface fluxes of sensible (and latent heat) at any of the building surface grid elements. 
 
-The technical realization of the topography and treatment of surface-bounded grid cells will be outlined in Sect. [wiki:doc/tec/topography topography implementation]. 
+The technical realization of the topography and treatment of surface-bounded grid cells is be outlined in Section [wiki:doc/tec/topography topography implementation]. 
+
+
+== Urban and natural surface schemes ==
+
+In order to simulate interactions between the atmosphere
+and the soil-vegetation continuum, an energy balance
+solver for natural surfaces in urban environments is essential to predict realistic
+surface conditions and fluxes of sensible heat and latent
+heat. When using the concept of the surface skin layer,
+where vegetation and bare soil fractions are considered
+to be flat and have a joint skin layer temperature, T skin ,
+the energy balance reads
+dT skin
+C skin
+ = Rn − H − LE − G ,
+dt
+(3.1)
+where Cskin is the heat capacity of the skin layer, Rn is
+the net radiation at the surface, H and LE are the tur-
+bulent surface fluxes of sensible and latent heat, and G
+is the heat flux into (or out of) the soil. Fluxes are de-
+fined positive (negative) when they are directed away
+(towards) the surface. A full interactive land surface
+scheme (LSM) was recently implemented in PALM,
+based on the Tiled European Centre for Medium-Range
+Weather Forecast Scheme for Surface Exchange over
+Land (Balsamo et al., 2009, TESSEL/HTESSEL, e.g.)
+and was first applied by Maronga and Bosveld (2017).
+The scheme consists of an energy balance solver for
+T skin and a multi-layer soil scheme that takes into ac-
+count the vertical diffusion of heat as well as vertical
+water transport in the soil. Vegetation is fully parameter-
+ized, including root extraction of water from particular
+soil layers used for transpiration and a prognostic equa-
+tion for the liquid water stored on plants by interception.
+So far, however, all vegetation is treated to be subgrid-
+scale, e.g. the canopy has no vertical extent and is pa-
+rameterized by aerodynamic parameters such as rough-
+ness lengths and heat capacity and conductivity of the
+skin layer. The land surface scheme is also applied for paved surfaces, which only deviates in the treatment of vegetated surface by different material properties and imperviousness to water.
+
+In order to simulate realistic urban environments, an adapted version of the land surface parameterization is available for building facade elements.
+Essentially, this involves the solution of an adapted version
+of Eq. 3.1 for each urban surface element, such as build-
+ing facades, roofs and impervious horizontal surfaces
+like pavement. For solving Eq. 3.1, the radiative transfer
+in the urban canopy, including multiple reflections and
+shading from buildings must be calculated, which may
+be considered to be one of the main challenging tasks
+in urban surface modelling (see Sect. 3.1.7). In order to
+estimate the heat flux G into the material, all building
+facades must be coupled to a multi-layer wall model.
+This is further complicated by the fact, that facades can
+not only consist of solid walls, but usually also consist
+of significant fractions of windows and sometimes green
+elements. Windows in particular have significantly dif-
+ferent physical properties than solid (greened) wall, e.g.
+in albedo, and they also allow shortwave radiation to en-
+ter the building.
+A preliminary version of an urban surface model
+(USM) has been recently entered the PALM default code
+(Resler et al., 2017), which already includes an energy
+balance solver for solid walls (see Fig. 5). In the course
+of MOSAIK we will take this as a basis to add the
+treatment of windows and green facades using the tile
+approach. Also, we will couple the USM to an indoor
+climate and energy demand model (see Sect. 3.1.6).
+
 
 
 == RANS turbulence parameterization ==
-
-== Land and urban surface model ==
-* refer to PALM's LSM