Changes between Version 2 and Version 3 of doc/tec/bc

Timestamp:

Apr 5, 2016 1:09:27 PM (9 years ago)

Author:

maronga

Comment:

--

doc/tec/bc

@@ -2 +2 @@
 
 == Constant flux layer ==
+
+=== Basics ===
 Following Monin-Obukhov similarity theory (MOST) a constant flux layer can be assumed as boundary condition between the surface and the first grid level where scalars and horizontal velocities are defined (''k'' = 1, ''z'',,MO,, = 0.5 ''Δz''). It is then required to provide the roughness lengths for momentum ''z'',,0,, and heat ''z'',,0,h,,. Momentum and heat fluxes as well as the horizontal velocity components are calculated using the following framework. The formulation is theoretically only valid for horizontally-averaged quantities. In PALM we assume that MOST can be also applied locally and we therefore calculate local fluxes, velocities, and scaling parameters.
 
@@ -114 +116 @@
 }}}
 
-Note that this implementation of MOST in PALM requires the use of data from the previous time step. The following steps are thus carried out in sequential order. First of all, ''θ'',,*,, and  ''q'',,*,, are calculated by integration using the value of ''z'',,MO,,/L from the previous time step. Second, the new value of ''z'',,MO,,/L is derived using the new values of ''θ'',,*,, and  ''q'',,*,, but using ''u'',,*,, from the previous time step. Then, the new values of ''u'',,*,,, and subsequently the momentum fluxes are calculated by integration, respectively. At last, the new surface fluxes are derived from ''θ'',,*,, and  ''q'',,*,,, and ''u'',,*,,. In the special case, when surface fluxes are prescribed instead of surface temperature and humidity, the first and last steps are omitted and ''θ'',,*,, and  ''q'',,*,, are directly calculated from ''u'',,*,, and the surface fluxes.
+=== Implementation ===
+Currently, there are three different options to calculate the Obukhov length and the surface fluxes which are steered via the NAMELIST parameter [wiki:doc/app/inipar#most_method most_method]. 
+
+==== {{{most_method = 'circular'}}} ====
+The traditional implementation in PALM ({{{most_method = 'circular'}}}) requires the use of data from the previous time step. The following steps are thus carried out in sequential order. First of all, ''θ'',,*,, and  ''q'',,*,, are calculated by integration using the value of ''z'',,MO,,/L from the previous time step. Second, the new value of ''z'',,MO,,/L is derived using the new values of ''θ'',,*,, and  ''q'',,*,, but using ''u'',,*,, from the previous time step. Then, the new values of ''u'',,*,,, and subsequently the momentum fluxes are calculated by integration, respectively. At last, the new surface fluxes are derived from ''θ'',,*,, and  ''q'',,*,,, and ''u'',,*,,. In the special case, when surface fluxes are prescribed instead of surface temperature and humidity, the first and last steps are omitted and ''θ'',,*,, and  ''q'',,*,, are directly calculated from ''u'',,*,, and the surface fluxes.
+
+Alternatively, the Obukhov length can be calculated by solving an implicit equation relating the ''L'' to the bulk Richardson number. This can be achieved either by a Newton iteration algorithm ({{{most_method = 'newton'}}}) or by using a lookup table ({{{most_method = 'lookup'}}}).