A T L M I X
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(1) Horizontal array dimensions are uniformly set to IDM,JDM. However, 
C-grid staggering considerations mandate that there be only (IDM-1)x(JDM-1) 
mass points. The distribution of water and land within the rectangle spanned 
by (IDM-1,JDM-1) is defined by the DEPTHS array [DEPTHS(I,J)=0 means land].

(2) The 2 time slots required for all prognostic and some diagnostic 
variables are incorporated into the third (vertical) array dimension. 
Generally speaking, the letter M [as in TEMP(I,J,KM)] stands for "mid" 
time, whereas N indicates the "new" and "old" time level.

(3) We recommend that the code be compiled with all variables preset to 
negative-indefinite. On Cray machines, this is accomplished by compiling 
with the "-ei" option and loading with the "-f indef" option. Grid values 
whose use in the various finite-difference operators is anticipated (and 
only those) are set to zero during model initialization. This provides some 
safeguard against contamination by "spurious" land data in case of 
unforeseen complexities in the coastline shape.

(4) As a result of the above, the program will crash if the DEPTHS array 
indicates the existence of single-grid-interval coastal inlets or channels. 
The MODS_1.3 patch can be used to detect and eliminate such features. (By 
changing the initialization procedure one may be able to overcome this 
restriction.) Single-point promontories and ultra-slim islands are okay.

(5)  There are no restrictions regarding the number of islands, but the 
parameter MS must be adjusted to the maximum number of "interruptions" of 
grid rows or columns by land. Specifically, MS-1 interruptions are allowed.
Interruptions in diagonal direction are governed by the parameter MD. If MS 
and/or MD are chosen too small, the program will stop in Subroutines BIGRID, 
INDXI, or INDXJ.

(6) The barotropic streamfunction is computed  o n l y  for diagnostic 
purposes. If the iteration count in the Poisson solver is set too low for 
the solution to converge, the model run itself will not be affected.

(7) Numerous diagnostic messages in the code are presently commented out 
("CDIAG") but can be activated as needed. Many of these messages refer to a 
specific grid point (ITEST,JTEST) which is defined in a DATA statement. 
Subroutine PRTIJ prints clusters of 5x5 grid variables in their proper 
spatial context.

(8) The model grid is defined on a Mercator projection of the earth's 
surface. Provisions for rotating the poles, i.e., choosing a geographic 
meridian as the "equator" of the projection, are made. Subroutine NEWOLD/
OLDNEW gives the location of (rotated) model grid points in relation to a 
lat/lon grid and vice versa. However, interpolation routines for translating 
fields of variables back and forth are the responsibility of the user.

(9) Error fixes, upgrades, etc., of model version 1.3 are listed in file 
MODS_1.3. One of these fixes eliminates a recently uncovered discrepancy 
between the model code and Eq. (16) in Appendix B of Bleck/Smith, JGR 1990.


                                                            Rainer Bleck