Configure a Lagrangian diagnostic: The Namelist file part 4/4
Hello, we're going to look at the last part
of the configuration of the Namelist file
using the 'ANA' tool.
This concerns the parameterisation
of the reading of the characteristics
of the model input grid.
This can be found in the
NEMO-OPA Meshmask, CROCO,
or ROMS Grid.
In the case presented here,
we are using the NEMO model,
which was selected at the beginning.
We need to fill in the location
of the NetCDF file,
in which there are
the characteristics of this grid.
We'll fill in the directory,
then the file name, which must be unique,
and several parameters.
The first parameter concerns
the longitudes at point 'T'.
the second, the longitudes at point 'U',
the third, the latitudes at point 'T',
and the fourth, the latitudes at point 'V'.
We also have to fill in
a description of the vertical,
consisting of the depths at point 'W'.
The next parameters,
from 'e2u' to 'e2t',
are the 'scale factors'.
If you click here,
a tab opens showing
a diagram
of a model mesh in NEMO
with each of these parameters:
'e2u', 'e1v' or 'e3t' for example.
These correspond to the widths,
lengths or heights
of each side of the cells.
In Ariane, we read the currents
but it is the transports that are used.
A transport = current * area
of a mesh in the model.
The transport we use
is the current multiplied by
the area of a side of a cell in the model.
I'm going back to the ANA tool.
Here, we'll fill in
the name of the variable
in the NEMO grid file
that corresponds to the scale factor
according to the description
given in this link.
The next parameter concerns
the dimensions of each mesh.
This is the 'vertical' parameter.
In an earlier module, we saw that
it is possible to fill in for NEMO
whether this is in partial steps or not.
If you are in a model
that does not use partial steps,
this will simply be a vector.
If you use partial steps,
it will be a 3D grid.
In Ariane (but not in ANA)
we also have the possibility to adapt
to the new NEMO V3 standards.
The second to last parameter concerns
the three-dimensional mask
in which the grid points
that are 'ocean'
or 'land' points are filled in.
For the 'land' points, we give the value
that's given in the 'tmask' 3D table.
Usually the value is 0
corresponding to land.
As in the case of NEMO,
if you select the model
CROCO or ROMS,
the heading will expand,
but the parameters will be different.
This time we have two headings,
one concerning the parameters
of the grid deformation,
which will be in a different file
from the other parameters
(longitudes, latitudes, scale factors).
Here, we fill in the directory
and the name of the NetCDF file
where we find these three parameters:
'hc', 'sc_w' and 'Cs_w'.
This content is normally
in the 'global attributes'
of your NetCDF files.
Let's move on to the second part of this section:
longitudes and scale factors
of your CROCO / ROMS grid,
which are in another file.
Therefore, you need to fill in the directory,
and the name of the grid file
where we find the longitudes at point 'rho' or 'T',
the longitudes at point 'U',
latitudes at point 'rho' or 'T',
and the latitudes at point 'V'.
As in the case of the NEMO model,
ROMS scale factors
are contained in two parameters:
'pm' and 'pn'.
We also need to fill in
the 'h' factor:
the minimum height of a level
in ROMS or CROCO.
Finally, the mask at point 'rho'
of the model must be a 2D table.
The ANA tool ends with a final item
that allows you to,
as well as saving the NetCDF file by default,
to save the data in a text file.
Most important, at the end of this page is the button:
'Print on screen a 'beautiful Ariane Namelist',
which will display the content
of the Namelist file that should be saved.
Just copy all the lines
and paste them into a text file.
I open a text editor and 'paste'.
I save all this information
in a file that I'll call 'namelist'.
Congratulations, you have made your Namelist file!
You now know how to:
- generate an Ariane executable file;
- fill in and interpret
the main parameters of a Namelist file;
- configure a Lagrangian analysis with Ariane.
You are now able to tackle
qualitative and quantitative diagnostics.
See you soon!