16.1.3.1 Example 1: One resolution domain

Imagine a grid with a longitudinal resolution $\Delta_\lambda=1^\circ$ encircling the earth and a meridional resolution $\Delta_\phi={1/3}^\circ$ equatorward of $10^\circ$N and $10^\circ$S, and a vertical grid spacing $\Delta_z=10$ meters between the surface and a depth of 100 meters. This domain and resolution is specified in the following manner. Two bounding longitudes: one at $0^\circ$E and the other as $360^\circ$E with $\Delta_\lambda=1^\circ$at both longitudes; two bounding latitudes: one at $-10^\circ$ and the other at $+10^\circ$ with $\Delta_\phi={1/3}^\circ$ at both latitudes; and two bounding depths: one at 0cm and the other at $100 \mbox{x} 10^2$cm with $\Delta_z=10 \mbox{x} 10^2$cm at both depths. These specifications imply 360 grid cells in longitude, 60 grid cells in latitude, and 10 grid cells in depth^16.1

The above is specified within the USER INPUT section of module grids by the following code:

c
c     "nxlons"  = number of bounding longitudes to define 1 region
c     "x_lon"   = bounding longitudes {0.0E, 360.0E}
c     "dx_lon"  = resolution centered at "x_lon" {1.0, 1.0}
c     
       parameter (nxlons=2)
       data (x_lon(i), i=1,nxlons)  /0.0, 360.0/
       data (dx_lon(i),i=1,nxlons)  /1.0,   1.0/
c
c     "nylats"  = number of bounding latitudes to define 1 region
c     "y_lat"   = bounding latitudes {-10.0, 10.0}
c     "dy_lat"  = resolution centered at "y_lat" {1/3, 1/3}
c     
       parameter (nylats=2)
       data (y_lat(j), j=1,nylats)  /-10.0,        10.0/
       data (dy_lat(j),j=1,nylats)  /  0.3333333,   0.3333333/
c
c     "nzdepths"  = number of bounding depths to define 1 region
c     "z_depth"   = bounding latitudes {0.0, 100.0m}
c     "dz_depth"  = resolution centered at "z_depth" {10m, 10m}
c     
       parameter (nzdepths=2)
       data (z_depth(k), k=1,nzdepths)  / 0.0,   100.0e2/
       data (dz_depth(k),k=1,nzdepths)  /10.e2,   10.e2/

Note that ``x_lon'' marks the edges of T-cells in longitude. Similarly, ``y_lat'' marks the edges of T-cells in latitude, and ``z_depth'' marks the edges of T-cells in depth. Also, ``dx_lon'' is the desired grid resolution at ``x_lon'' which is the longitude of a U-cell (not the T-cell). Since MOM uses an Arakawa B grid, the U-cell grid points are at the vertices of the T-cells and visa versa when looking down at the grid toward increasing depth. A U-cell with coordinates (i,j) is on the northeast vertex of a T-cell with coordinates (i,j). In the vertical, U cells and T cells are at the same level. More on this later.