Here we explain the CANDIE A-gird, or more precisely,
the CANDIE mixed
A-grid and C-grid model configuration. This is perhaps best shown
graphically in
Fig. 3, which shows a horizontal cross section of the fluid grid cells.
There are **IO** cells
in the X-direction numbered left to right (west to east) ** I**=1,2,...,
** I0**,
and ** J0** cells in the Y-direction numbered bottom to top (south to north)
** J**=1,2,...,** J0**.
The values ** IO** and ** J0** are specified by the user.

The black dot at the center of each grid cell in Fig. 3 is a model A-grid
point. The CANDIE array variables calculated at these points are represented
by the pressure array ** P**, and have array dimensions** (IO, JO )**
in the (X,Y)
directions. The CANDIE scalar variables are calculated at these A-grid points. Some of these scalar variables are
the pressure ** P(I0,J0,K0)**, surface pressure ** PS(I0,J0)**,
temperatures ** T1(I0,J0,K0)** and ** T2(I0,J0,K0)**,
salinities ** S1(I0,J0,K0)**
and ** S2(I0,J0,K0)**, and density ** RHOP(I0,J0,K0)**, where ** K0**
is the array dimension
in the vertical Z-direction.
The A-grid CANDIE vector variables
calculated at these points are the X-direction velocities ** U1(I0,J0,K0)**
and ** U2(I0,J0,K0)**, and
the Y-direction velocities ** V1(I0,J0,K0)** and ** V2(I0,J0,K0)**.
The vertical
velocity ** W(I0,J0,K0)** is also
calculated at the A-grid points but at a different level in the vertical.
The model forcings such as wind stresses ** TAUX(I0,J0)** and
** TAUY(I0,J0)**,
and the heat and salinity fluxes
are also applied at the surface A-grid points.

The Fig. 3 also shows the C-grid advective velocities used for the
conservation equations, used in calculating fluxes into and out of the cell
volume. The X-direction ** U** advective velocity point is marked by a cross, and the
Y-direction ** V** advective velocity point is marked by a square.
These C-grid
advective
velocity arrays have different dimensions from the A-grid variable arrays. If we denote ** IP**=** I0**+1 and ** JP**=** J0**+1, then we have
** U(IP,J0,K0)** and
** V(I0,JP,K0)**.

The CANDIE model uses an elliptic solver for the surface pressure, so that
the model boundaries require special attention. The grid cells at the
boundary must be either land cells, or if at an open boundary the
open boundary conditions must be specified there. The one grid cell border all
around the domain is referred to as the ``ghost zone", and is marked as
the shadded region in Fig. 3. Of course, land points can also be in the
interior of the domain, and the model can also accomodate islands
within the domain. A discussion of how to set up the grid will be given later
when discussing the * prep*.F file and model preparations.