GMODEL

Version: 3.0
Author: Gerrit Burgers (e-mail: burgers@knmi.nl, www: http://www.knmi.nl/~burgers )

Description
GMODEL is a linear coupled model of the equatiorial Pacific that consists of three components:

1. A linear shallow water ("1.5 layer") model of the equatorial Pacific. Its domain is 30S-30N, 122E-292E, on a 2x1 degree grid with realistic boundaries. Its only dynamical field is the thermocline depth.
2. A simple SST-equation that is valid only in the central and eastern equatorial Pacific. The SST is influenced by thermocline depth and by zonal windstress anomalies. The SST equation has three linear terms:
   • a linear damping
   • a forcing proportional to the thermocline anomaly
   • a forcing proportional to the zonal windstress anomaly
   All three terms depend on longitude.
3. A two-pattern statistical atmosphere driven by the NINO3 and NINO4 indices and noise terms. The coefficients of the two patterns are of the form: a*NINO3+b*NINO4+noise

The time is kept in days, using 12 months of 30 days.

Application Area
GMODEL gives a reasonable description of the SST variability in the central and eastern equatorial Pacific. An advantage is its speed: of the order of seconds per model simulation year.

Installation
First one need to gunzip and unpack the tar.gz file. This creates a directory Gmodel. Change to this directory. Directories The Model directory contains the Fortran source code of GMODEL. The executable is named Shallow. The source files that one may want to edit include:

• bahr.f, the main program
• starts.f, sets various ocean parameters
• ssteqs.f, the SST equation
• stoatm.F, the statistical atmosphere,
• shallow.f, the shallow water model.

The directory Forced contains the script forced.sc to run GMODEL in forced mode. This requires the files pacano99.ext and fsumask from the directory Wind.

The directory Coupled contains the script coupled.sc to run GMODEL in coupled mode. This requires the files atmtwoa.ext from the directory Statatm and fsumask from the directory Wind.

The directory Fsu contains the FSU wind data.

The directory Wind contains the input files for forced runs. The file fsumask contains the land-sea mask of the FSU winds. The makefile can be used to compile and run the program anoplain.f to create the file pacano99.ext which is needed to run GMODEL in forced mode.

The directory Statatm contains the files for coupled runs. The program constratm2a.f to create the file atmtwoa.ext that is need to run GMODEL in coupled mode. Note that this program calculates seasonal patterns too, but these are not used by the statistical atmosphere of GMODEL. The program constratm2a.f need the file pacano99.ext from the Wind directory. You can use make to compile and run the program. The diagnostic program projtwoa.f can be used to look into the projection of the FSU winds on the windfield patterns.

Next, check the FC and FFLAGS variables in the makefiles in the subdirectories Model, Wind and Statatm. Modify these variables if necessary. Then, type

make demo

The FORTRAN source files of Gmodel are located in the subdirectory Model. The executable is named 'Shallow' and requires approximately 1.5 MB of memory to run. The demonstration runs each take about four minutes to complete on a Linux PC with a 733 MHz Pentium III.

Configuration
Parameters
The tables below list the parameters and variables that can be modified in the parameter block parames and the source file starts.f and their default value. Note that after changing these parameters, the program must be re-compiled.

The variables of the GMODEL simulation code.

Parameter	Description	Default Value
coc	The square of the velocity of Kelvin waves	(2.2 m/s)2
och	Depth of the mean thermocline	150m
dtoc	The time step	1/3 day
rkt	Overall factor in SST equation (see ssteqs.f)	0.0635
rnuhoc	biharmonic diffusion of height	2000
rnumoc	biharmonic viscosity	20000
rks	drag coefficient	0.0015
xwest	western boundary grid	123
xeast	eastern boundary grid	291
xnorth	northern boundary grid	29.5
xsouth	southern boundary grid	-29.5

Input Files
The input files that are required to run the GMODEL simulation code are listed in the table below.

The input file 'control.in' has the following format:

A one line comment
A one line experiment identifier
0/1	Is this a restart of a run?
0/1	Is this a coupled run?
n	The number of days to run
yyyymm	The starting year and month

Results
The program creates the several output files in which it stores the results of the simulation. These files are listed in the following table.

All files with the extension .ext are in the MPI "extra" format and are unformatted FORTRAN data files with the following structure:

Record No.	Contents
1	yyyymmdd	field	level	size
2	(field(i), i=1,size)
...	...

Source Code
If the run is to be driven by a wind or heatpatch instead of FSU winds do the following:

1. program your favorite patch in subroutine patch.f
2. edit the main program bahr.f to use the subroutine in patch.f to read the patch data instead of the subroutine in stress.f which reads the FSU winds.

Demo Run
In the main GMODEL directory one can enter the command

make demo

Support
GMODEL is supported at the S0 level (see also the page on support levels). For any question about GMODEL one can contact the author Gerrit Burgers (e-mail: burgers@knmi.nl).

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