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Model Grid

 

The grid-scale variables in the QTCM1 are located on a staggered C-grid [28] of dimensions tex2html_wrap_inline1471 , where the x (zonal, longitudinal) coordinate indexes from 1 to NX, and the y (meridional, latitudinal) coordinate indexes from 1 to NY. (there are certain exceptions to this description of the dimensioning, which are noted in Section gif). A schematic of the grid is given in Figure gif.

   figure323
Figure: QTCM1 staggered C-grid. Note that j=0 only exists for v and variables dependent on v. See text in Section gif for details.

The pair (i,j) denotes a grid point. For the standard version, tex2html_wrap_inline1359 and tex2html_wrap_inline1361 . Figure gif abbreviates variables as follows:

tabular333

These variables are all prognostic.

Thus, temperature is located at grid point (i,j), while zonal velocity is located at ( tex2html_wrap_inline1491 ), meridional velocity is located at ( tex2html_wrap_inline1493 ), and tex2html_wrap_inline1495 is located at ( tex2html_wrap_inline1497 ). Recall that the subscript ``0'' refers to the barotropic mode, while the subscript ``1'' refers to the baroclinic mode.

Other variables are also defined at the above locations. These include:

tex2html_wrap_inline1499
Located at the same position as T. Variable tex2html_wrap_inline1499 is the surface temperature, and is received from the ocean, except over land where it is prognostic.

tex2html_wrap_inline1503
Located at the same position as T. Variable tex2html_wrap_inline1503 is the humidity, and is prognostic.

tex2html_wrap_inline1507
Located at the same position as vort0. Variable tex2html_wrap_inline1507 is the barotropic streamfunction, and is diagnostic from vort0.

All other model variables are diagnostic, and are centered at (i,j) on the grid.

Although the C-grid has half-step variable indices, array indices in FORTRAN do not. Thus, we have adopted the convention that all half-indices are truncated when referred to in the QTCM1 code. For example:

tabular348

In all other sections of this document, array indice naming follows the FORTRAN model code convention.

Below is a portion of the file qtcm.h which contains the array declarations for the main prognostic grid variables:

c baroclinic mode
      real*8 u1(NX,NY),v1(NX,0:NY),T1(NX,NY),q1(NX,NY)

c barotropic mode V0; note only vort0 and u0bar are prognostic
      real*8 u0bar,u0(NX,NY),v0(NX,0:NY),vort0(NX,NY),psi0(NX,0:NY)

c- Boundary inputs and derived; exception: Ts overland is prognostic
      real*8 Ts(NX,NY),qs(NX,NY),Ts0(NX,NY)


next up previous contents
Next: Model Code and Numerics Up: Calling Structure and Grid Previous: Model Code Calling Tree

Hui Su
Thu Nov 16 00:53:31 PST 2000