              USER'S GUIDE FOR THE ZEBIAK/CANE COUPLED MODEL
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     Following is a brief description of the Zebiak and Cane 1987 (MWR;
hereafter ZC) model code and how to use it.  The governing equations of the
model are presented in ZC, and will not be reviewed here.  The model computes
anomalies of atmospheric and oceanic fields, relative to a specified monthly
mean climatology, for the tropical Pacific region.

     Several of the model parameters are trivially adjustable (these are 
reviewed below, but the time step and spatial grids cannot be adjusted without 
some recoding.  The standard value time step is (about) 10 days;  the standard 
value grid for ocean dynamics is 2 degrees longitude by .5 degrees latitude;  
the standard grid for SST physics and atmosphere model is 5.625 degrees 
longitude by 2 degrees latitude.  

     The model uses an unorthodox time convention in which time is measured
in "months" subsequent to January 1 1960.  These "months" are defined to be
exactly 1/12 of a year in duration, and they therefore differ slightly from the
actual calendar months, which have variable length by up to 3 days.  However,
in both the model convention and the real calendar, 12 months corresponds to
exactly one year.  The time 0.5 corresponds to mid-January, 1960 in the model
convention.  The time 12.5 corresponds to mid-January, 1961.  The time 330.5
corresponds to mid-July 1987, etc.

     The makefile "makezeqfc1" can be used to generate the object files and
executable file "zeqfc1" on any standard unix system.  It is assumed that
the IMSL library is available; makezeqfc1 invokes this with the -limsl flag - 
on different systems this should be modified to provide proper linking to IMSL.

     Several data files are necessary to run the coupled model.  These include:

     rcwndmn.data - climatological monthly mean surface winds for trop. Pac.
     rcdivmn.data - climatological monthly mean surface wind divergence
     rcsstmn.data - climatological monthly mean sea surface temperature
     wem.zeb - simulated climatological monthly mean oceanic upwelling
     uv.zeb - simulated climatological montly mean surface hor. currents

These files are read in binary form in subroutine SETUP2.  In addition to
these climatological files, an input data file provides desired parameter
values and other information to the coupled model.  A sample is found in the 
file fctest.data.  Each input line, in sequential order, is described below:

1. case title.  This is just an ascii string that will appear on the standard
output.

2. filename of history input file.  The program will open this file and 
attempt to read from it in order to initialize the model, if parameter NSTART 
is > 0.

3. filename of history output file.  Output will be written to this file at 
the very end of model run, and possibly at other times (see NTAPE).  The
information is sufficient to allow another model run to restart.

4.  NSTART; controls initialization.  If NSTART=0, the coupled model starts
up from a state of no anomalies.  In this case an imposed anomaly of some
sort is needed to start up the model (see discussion under NIC).  If NSTART=2,
initial conditions are read from history input file (line 1) and time is set
to the value corresponding to those conditions in the history file.  If 
NSTART=3, history input is also obtained from the history file, but time is
reset to the value specified in the TZERO parameter.

5.  TFIND;  when history file is being used (NSTART>0), TFIND specifies the
time being sought for initialization.  The history file will be searched
until the time TFIND is located, and initial fields will be gotten for that
time to start the coupled run.

6.  NX;  the number of longitudinal v-points in ocean dynamics model.  
According to the model's staggered grid, the number of u and h points is one
greater (NX+1). Though the ocean dynamics can be run with other values of NX, 
the SST physics assumes the standard value of 78.

7.  NY;  the number of latitudinal u and h points in the ocean dynamics model.
The number of v points is one greater (NY+1). SST physics assumes the standard 
value of 115 for NY.

8.  HEQUIV;  the oceanic equivalent depth.  SST physics assumes the standard
value of 86 (cm.).

9.  TZERO;  the initial time for the run (ignored if NSTART=2).

10. TENDD;  the final time for the run.  Must be larger than TZERO (larger
than TFIND if NSTART=2).

11.  DTD;  the time step in "months".  SST physics assumes the standard value
of .3333334.

12.  XWD;  westernmost limit of ocean basin (a u/h point).  SST physics assumes
the standard value of 124 (degrees E).

13.  XED;  easternmost limit of ocean basin (a u/h point).  SST physics assumes
the standard value of 280 (80 degrees W).

14.  YSD;  southernmost limit of the ocean basin (a v point).  SST physics 
assumes the standard value of -28.75 (28.75S).

15.  YND;  northernmost limit of the ocean basin (a v point).  SST physics 
assumes the standard value of 28.75 (28.75N).

16.  TDECAY;  the timescale of interior ocean dissipation in months.  Standard 
value is 30.

17.  TPLMIN;  earliest time that history output will be written.

18.  NPRINT;  interval, in timesteps, between diagnostic output lines for
ocean dynamics written to standard output. 

19.  NSEG;  the number of rectangular subsections making up ocean model
basin.  SST physics assumes standard value of 1 (ocean basin is a simple
rectangle).

20.  YNORTH;  should be the same as YND for NSEG=1.

21.  YSOUTH;  should be the same as YSD for NSEG=1.

22.  XWEST;  should be the same as XWD for NSEG=1.

23.  NTAPE;  if 0, write history output only at last timestep of run (written
to file identified on line 2 of data file.).  If NTAPE>0, history output is
written every NTAPE timesteps, provided time variable is greater than TPLMIN.

24.  NREWND;  controls rewinding of history tape.  Always has the form of a
two digit integer IJ, where both I and J are either 0 or 1.  If I=1, history
input tape is rewinded after each read, whereas if I=0, history input is not
rewinded.  If J=1, history output file is rewinded after each write (so 
subsequent writes overwrite each other). J=0 precludes rewinding of history
output.

25.  NATM;  coupling paramter.  NATM=2 implies ocean and atmosphere are
coupled (no other value should be used without code changes).

26.  IC2;   a parameter that could be used to specify additional types of
initialization (e.g., overwriting the history input with data from some other
source, etc).  At present, the parameter is not active, but see zeq1main.f.

27.  GAM1;  parameter affecting strength of mean upwelling advection term in
SST equation.  Standard value is .75.

28.  GAM2;  parameter affecting strength of anomalous upwelling advection tern
in SST equation.  Standard value is .75. 

29.  TDA1;  parameter affecting amplitude of subsurface temperature anomaly
for positive h perturbations. Standard value is 28.

30.  TDB1;  parameter affecting the nonlinearity of subsurface temperature
anomaly for positive h perturbations. Standard value is 1.25.

31.  TDA2;  parameter affecting amplitude of subsurface temperature anomaly
for negative h perturbations. Standard value is -40.

32.  TDB2;  parameter affecting the nonlinearity of subsurface temperature
anomaly for negative h perturbations. Standard value is 3.0.

33.  TLOSS; parameter affecting surface heat flux (a linear damping on 
SST anomaly).  Standard value is .98, corresponding to a 125 day decay time.

34.  ALPHA; parameter controlling strength of SST-related component of 
atmospheric heating.  Standard value is 1.6.

35.  EPS;   atmospheric friction parametea.  Standard value is 0.3,
corresponding to about a 1 day damping time.

36.  BETA;  parameter controlling strength of convergence feedback portion
of atmospheric heating. Standard value is .75.

37.  CTOL;  threshold value for maximum differences in wind divergence between
successive atmospheric model iterations.  If this value is exceeded, another 
iteration is done (provided the number of iterations has not exceeded IMAX).
Standard value is .15.

38.  IMIN;  the minimum number of atmospheric model iterations allowed (not
counting the first).  Standard value is 1.

39.  IMAX;  the maximum number of atmospheric model iterations allowed (not
counting the first). Standard value is 2.

40.  ISTEP; logical parameter controlling whether full anomaly field is
recomputed at each timestep (false), or if the anomaly field is only 
incremented for some timesteps (true). Standard value is .true.

41.  TCUT;  a time value after which external wind forcing (used to perturb
the zero anomaly state when no history input is being used) is removed. Only
used is NIC > 0.

42.  TSEED; a real number used to initialize a random number generator routine
in runs where external random forcing is added (NIC=1 only).

43.  TAMP1; parameter governing the strength of external stress perturbation.

44.  TAMP2; additional parameter governing external stress perturbation if
NIC=1.

45.  JLEFT; westernmost limit (expressed as an array index) of external stress
perturbation.

46.  JRT;   easternmost limit (expressed as an array index) of external stress
perturbation.

47.  ITOP;  northernmost limit (expressed as an array index) of external stress
perturbation.

48.  IBOT;  southernmost limit (expressed as an array index) of external stress
perturbation.

49.  NIC;   parameter governing external stress perturbations.  For NIC=0
there is no external stress perturbation.  For NIC=1 a stochastic external 
zonal stress is added within the limits imposed by jleft,jrt,itop,ibot, with
characteristics governed by tamp1,tamp2.  For NIC=4, a uniform zonal wind
stress patch is imposed between the same limits, for times up to TCUT, after
which there is no external forcing.

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Model variables.

Following is a list of the more important model arrays organized by grid type 
and convention. The first are ocean arrays, with the index I corresponding to
longitude and running from west to east, and the index J corresponding to 
latitude, and running from south to north.

1. AKB(I) I=1,NX+1 
     describes the amplitude of oceanic Kelvin wave, which is updated 
     analytically by the ocean dynamics model.

2. PHIK(J) J=1, NY 
     gives the meridional structure of the oceanic Kelvin mode.

3. UB(J,I), J=1,NY; I=1,NX+1
     the Rossby component of depth integrated zonal current between the 
     thermocline and surface.  To get the entire depth integrated zonal
     current anomaly one must add the Kelvin component as follows:
          U(J,I)=UB(J,I)+AKB(I)*PHIK(J).  
     Units of UB and U as defined are nondimensional, but for the standard
     parameters of the model, multiplication by 2.0 gives currents is cm/s.

4. V(J,I), J=1,NY+1; I=1, NX
     the depth integrated meridional current anomaly between the thermocline 
     and surface. For standard parameters, multiplication by 2.0 gives cm/s.

5. HB(J,I), J=1, NY; I=1,NX+1
     the Rossby component of upper layer depth anomaly.  To get the entire
     upper layer depth anomaly, one must add the Kelvin component as follows:
           H(J,I)=HB(J,I)+AKB(I)*PHIK(J).
     Units of HB and H as defined are in meters.


The following arrays have index I corresponding to longitude and running from
west to east, and the index J corresponding to latitude and running from
north to south. I=1 corresponds to 101.25E, with successive points 5.625 
degrees apart (the points within the standard ocean basin are i=6, 32,
corresponding to 129.375E and 84.375W respectively). J=1 corresponds to 29N,
with successive points 2 degrees apart (J=30 corresponds to 29S).

6.  TO(J,I), J=1, 30; I=1, 34
      SST anomaly field.  Nonzero values are found only beteen i=6,32 and
      j=6, 25 (SST anomaly is not computed poleward of 19N and 19S). Units 
      are degrees C.

7.  UO(J,I), J=1,30; I=1, 34
      surface zonal wind anomaly, in units of m/s.

8.  VO(J,I), J=1,30; I=1,34
      surface meridional wind anomaly, in units of m/s.

9.  DO(J,I), J=1,30; I=1, 34
      surface wind divergence anomaly. Multiplication by 0.9 gives units of
      10**-6/s.

10. QF(J,I), J=1,30; I=1, 34
      nondimensional atmospheric heating anomaly.  Division by 52.3
      gives heating rate per unit mass (m**2/s**3).

11. US(J,I), J=1,30; I=1, 34
      surface layer zonal current anomaly in cm/s.  Nonzero values only for 
      i=6,32 and j=6, 25.

12. VS(J,I), J=1,30; I=1, 34
      surface layer meridional current anomaly in cm/s.  Nonzero values only
      for i=6,32 and j=6, 25.

13. WP(J,I), j=1, 30; I=1, 34
      upwelling velocity at base of surface layer (50m) in units of 
      10**-3 cm/s. Nonzero values only for i=6,32; j=6,25.

14. H1(J,I), j=1, 30; I=1, 34
      oceanic upper layer depth averaged onto coarser grid.  Units are m,
      meaningful domain is i=6,32; j=6,25.

15. U1(J,I), J=1, 30; I=1, 34
      depth averaged zonal current (see UB above), averaged onto coarser grid.
      Meaningful domain is i=6,32; j=6,25.

16. V1(J,I), J=1, 30; I=1, 34
      depth averaged meridional current (see V above), averaged onto coarser
      grid. Meaningful domain is i=6,32; j=6,25.

17. TT(J,I), J=1, 30; I=1, 34
      total SST field in degrees C. Meaningful domain is i=6,32; j=6,25.


The following array has index I corresponding to longitude and running from
west to east, and the index J corresponding to latitude and running from
south to north. I=1 corresponds to 101.25E, with successive points 5.625 
degrees apart (the points within the standard ocean basin are i=6, 32,
corresponding to 129.375E and 84.375W respectively). J=1 corresponds to 29S,
with successive points 2 degrees apart (J=30 corresponds to 29N).

18. HTAU(I,J,K), I=1, 34; J=1, 30; K=1, 2
      surface wind stress anomaly, in dy/cm/cm. The third index corresponds
      to vector component, with K=1 denoting zonal and K=2 denoting meridional
      component.

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At least one scalar variable is of interest:

1. TD;   time variable in the coupled model

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Output for these variables can be obtained by inserting write statements
in the main program (zeq1main.f) at the indicated position.


