Table of contents
Chapter 1. Overview
Chapter 2. Radiation
Chapter 3. Turbulent diffusion and interactions
with the surface
Chapter 4. Subgrid-scale orographic drag
Chapter 5. Convection
Chapter 6. Clouds and large-scale precipitation
Chapter 7. Land suface parametrization
Chapter 8. Methane oxidation
Chapter 9. Climatological data
REFERENCES
|
|
Next
Section
Previous Section
Vertical diffusion, which affects temperature, velocities and specific humidity,
is performed in subroutine VDFMAIN called by VDFOUTER
which, in turn, is called by CALLPAR. VDFOUTER calls VDFMAIN three times
with 1/3 of the normal time step (these two routines have identical arguments
so VDFMAIN can be called directly if the vertical diffusion is only needed
once per time step).
At the start of the model integration the following setup routines are called
to initialize modules specific to the vertical diffusion code:
| |
• SUVDF. Setup routine for a number of
parametrization constants. |
| |
• SUVDFS. Setup routine for constants and
tables related to the stability functions. Stability functions are
included as statement functions from fcvds.h. |
| |
• SUVEG. Setup routine for vegetation and
tile parameters. |
The main subroutine (VDFMAIN) does a sequence of computations and subroutine
calls:
| |
• The tiled surface fluxes and tiled skin
temperatures are cycled from time step to time step (fluxes are needed
for the first guess of stability parameters), but are not available
at the start of the forecast. For the first time step, neutral transfer
coefficients are used to estimate momentum fluxes, the tiled skin
temperatures are set equal to the grid box averaged skin temperature
from the initial condition, and the sensible and latent heat fluxes
needed as a first guess for the Obukhov length computation are set
to zero. |
| |
• VFDUPDZ0. This routine computes roughness
lengths for momentum, heat and moisture over ocean surfaces according
to equation (3.24). It also computes surface
buoyancy flux and Obukhov length from the fluxes of the previous time
level. |
| |
• The dry static energy is computed on
model levels. |
| |
• A grid box average of the surface albedo
is computed from the tile albedo and the tile fractions. |
| |
• VDFSURF. This routine prepares the surface
boundary conditions for temperature and humidity and is called for
every tile. The following quantities are computed: the surface specific
humidity at saturation, the derivative of the saturation humidity
curve at the surface, surface dry static energy, and vegetation stomatal
resistances (see Chapter 7). |
| |
• VFDEXCS. This routine determines the
drag transfer coefficients between the surface and the lowest model
level with the thermal stability expressed as function of the Obukhov
length. It is called for every tile. The implicit relation between
 and the Richardson number  is solved iteratively (using the Newton method with the derivative
approximated in finite differences). Pre-computed tables defined in
subroutine SUVDFS are used to obtain the first guess in stable conditions
(Ri>0) at the first time step. Transfer coefficients are
multiplied by a constant factor  . |
| |
• VDFEVAP. This routine computes for each
tile the equivalent evapo-transpiration efficiency and the corresponding
parameters  and  defined by the land surface scheme (see chapter 7). Dry static energy
at the surface at time level  is estimated as well. |
| |
• VDFSFLX. This routine computes surface
fluxes for each tile (heat flux, evaporation, momentum flux and virtual
heat flux) at time  for later use in similarity functions and for the estimation of the
diagnostic boundary layer depth. |
| |
• VDFDPBL. This routine diagnoses the boundary
layer height for time level  . This boundary layer height is for postprocessing only and is not
used by the parametrization. |
| |
• VFDEXCU. This routine determines the
turbulent diffusion coefficients between the model levels above the
surface layer. In unstable surface conditions, the depth of a mixed
layer is estimated where the diffusion coefficients are expressed
according to equations (3.36) and (3.37). Above the mixed layer, the
diffusion coefficients are expressed from local similarity theory
with equations (3.31) if Ri<0. In layers with
Ri>0, diffusion coefficients are expressed as function of
the Richardson number according to equation (3.32). The entrainment rate at the
top of the mixed layer is computed according to
(3.40). |
| |
• VDFDIFM. This routine solves the diffusion
equation for momentum, by Gaussian elimination of the tridiagonal
matrices. |
| |
• VDFDIFH. This routine solves the diffusion
equations for dry static energy and specific humidity. A downward
elimination scan is done through the tridiagonal matrices, and coefficients
 ,  ,  , and  are computed for each tile. Then, subroutine VDFTSK is called for
each tile to compute the skin temperatures from the surface energy
balance equation. Subsequently the tiled skin temperatures are used
as a boundary condition and the back-sustitution is performed. |
| |
• VDFINCR. This routine computes the tendencies
of the prognostic variables and estimates the kinetic energy dissipation. |
| |
• VDFTFLX. This routine computes the tile
fluxes at the new time levels. These are also the fluxes to be used
in the land surface scheme. Averaging over the tiles is also done
for diagnostic purposes and postprocessing. |
| |
• VDFPPCPL. This routine computes the surface
2 metre temperature and humidity (dew point and specific humidity),
and the wind at 10 m. |
| |
• VDFPPGUST. This routine computes wind
gusts as they are typically observed by standard WMO SYNOP stations. |
Next Section
Previous Section
|
