Model Domain Boundary Condition (jperio)
At the model domain boundaries several choices are offered: closed, cyclic east-west,
south symmetric across the equator, a north-fold, and combination closed-north fold
or cyclic-north-fold. The north-fold boundary condition is associated with the 3-pole ORCA mesh.
Closed, cyclic, south symmetric (jperio = 0, 1 or 2)
The choice of closed, cyclic or symmetric model domain boundary condition is made
by setting jperio to 0, 1 or 2 in namelist namcfg. Each time such a boundary
condition is needed, it is set by a call to routine lbclnk.F90. The computation of
momentum and tracer trends proceeds from to and from to
, in the model interior. To choose a lateral model boundary condition
is to specify the first and last rows and columns of the model variables.
- For closed boundary (jperio=0)
- , solid walls are imposed at all model
boundaries: first and last rows and columns are set to zero.
- For cyclic east-west boundary (jperio=1)
- , first and last rows are set
to zero (closed) whilst the first column is set to the value of the last-but-one column
and the last column to the value of the second one (Fig. 8.3-a).
Whatever flows out of the eastern (western) end of the basin enters the western
(eastern) end. Note that there is no option for north-south cyclic or for doubly
- For symmetric boundary condition across the equator (jperio=2)
last rows, and first and last columns are set to zero (closed). The row of symmetry
is chosen to be the - and points equator line (, i.e. at the southern
end of the domain). For arrays defined at or points, the first row is set
to the value of the third row while for most of - and -point arrays (, ,
, but scalar arrays such as eddy coefficients)
the first row is set to minus the value of the second row (Fig. 8.3-b).
Note that this boundary condition is not yet available for the case of a massively
parallel computer (key_mpp defined).
setting of (a) east-west cyclic (b) symmetric across the equator boundary conditions.
North-fold (jperio = 3 to )
The north fold boundary condition has been introduced in order to handle the north
boundary of a three-polar ORCA grid. Such a grid has two poles in the northern hemisphere
(Fig.16.1, and thus requires a specific treatment illustrated in Fig.8.4.
Further information can be found in lbcnfd.F90 module which applies the north fold boundary condition.
North fold boundary with a -point pivot and cyclic east-west boundary condition
(), as used in ORCA 2, 1/4, and 1/12. Pink shaded area corresponds
to the inner domain mask (see text).
Gurvan Madec and the NEMO Team
NEMO European Consortium2017-02-17