CHyM Libraries

CHyM model Version 5.00 documentation
Source code available for local users only
The basic equations of CHyM model are available here.
Last update: February 19, 2022.

This page is organized with four different tables. In the first table the general purpose routines available in the chym library are listed and documented. In the second table a complete description of CHyM internal flags written in the header of the output file is reported. In the third table the CHyM script parameters are listed and described. The table 4 lists the arrays used inside CHyM fortran code and related meaning. The documentation of CHyMLab utility is now also available.

General concept about the use of CHyM model

Run o restart
CHyM model

CHyM model can be runned for a new simulation or restared form a previous output depending on the script flag RESTART descript in the third table.

RESTART = 0 means that a new run is started and a new output file must be created. The static fields are calculated from the CHyM database and dynamical fields are initialized with a null value, more specifically the arrays port, gh2o, bwet, deepw and snow are set to zero. Of course, in this case, an adeguate phase of spin-up is needed before resonable values of dynamical fields are reached.
RESTART = 1 means that a new run is started and a new output file must be created, but the domain and the resolution is the same of a previous simulation. In this case the static fields are read from the specified by RFILE script parameters. In order to avoid confusion and not coeherent definition of different parameters, CHyM code check, after acquiring the script parameters, that the parameters NLON, NLAT, SLON, SLAT and DIJ are the same of the domain with which RFILE file has been produced; if this is not the case, an appropriate errore massage is displayed and code is stopped.
The dynamical fields are initialized with a null value, more specifically the arrays port, gh2o, bwet, deepw and snow are set to zero and, also in this case, an adeguate phase of spin-up is needed before resonable values of dynamical fields are reached.
RESTART = 2
....to be completed....
CHyM model also creates a file for a "quick" restart. The filename is created

Table 1. General purpose fortran subroutine included in the CHyM library

Reading CHyM output file

chymreadstaticfields([lun/file],[flag])

Read from the source specified by the first argument the CHyM static fields. This data will be stored in the arrays defined within the chymdata module. This subroutine also read the header of the file containing the vectors mchym, rchym and schym.
chymreadstaticfields is actually an interface (means that the name of the subroutine is the same, but you may invoke it using a different combination of arguments) and you may invoke it in four different ways namely specifying the file name or logic unit (first argument) and specifying (or not) a two digit integer option as second argument; if the second argument is not specifyed the value 00 for it is assumed.

If an integer is passed as first argument the fields are read form this logic unit; if a string is passed as first argument, the subroutine assumes that this argument specifyes the filename to be opened in a free logic unit, in this case the the file is closed after reading the fields.
Valid options for the integer flag are 00, 01, 10 and 11. More specifically: If the second digit is = 1, this subroutines check whether or not the parameters defining the grid written in the file corresponds to the grid defined by the parameters that are currently stored in the mchym/rchym vectors (this option is usually used by CHyM model in order to restart from a previous run); if the first digit is 1 a short list of info is given on standard output, specifying the grid and other informations about the CHyM output you are reading.

The subroutine chymreadstaticfields provides a very simple way to retrieve the basic fields of a CHyM simulation. As an example to plot the DEM of the selected domain only a three-line program is needed:

	use chymdata , only : chymreadstaticfields
	call chymreadstaticfields('tmp/Po.chym')
	call chymplot(1,'dLl')

chymreaddynamicfields(lun)

Read from the logic unit specified by the argument the CHyM dynamical fields and store them in the arrays defined within chydata module; each time you invoke this routine the next time step is read and variable time is also updated. If the CHyM grid is not yet defined this routine also call chymreadstaticfields in order to define it; to plot and manage dynamical is consequently very simple, as an example to plot the rain at the first time step, the following few lines are enough:

	open(10,file='../chym/tmp/test.chym',status='old',form='unformatted')
	call chymreaddynamicfields(10)
	call chymplot(6,'dLlc2')

You may also manipulate the data stored in the CHyM module, adding the use statement in your code and specifying the list of arrays you want to manipulate, these arrays are descript in the table 4, the list also includes two "work arrays" wkm1 and wkm2, you may want to use these arrays insteand to define an new allocatable array as in the example reported below. In the following example the plot of cumulative rain is produced.

	use chymdata , only : rain,nlon,nlat,mchym,chymreadstaticfields
	real , allocatable , dimension(:,:) :: myrain
	open(10,file='../chym/tmp/test.chym',status='old',form='unformatted')
	call chymreadstaticfields(10)
	allocate(myrain(nlon,nlat)) ; myrain=0
	do i=1,mchym(6)
	   call chymreaddynamicfields(10)
	   myrain=myrain+rain
	enddo
	rain=myrain
	call chymplot(6,'Llc2')
	call displayplot(' ','Total accumulated rain',' ')

The list of table 4 also includes two "work arrays" wkm1 and wkm2, you may want to use these arrays insteand to define an new allocatable array as in the previous example as follow.

	use chymdata , only : rain,wkm1,nlon,nlat,mchym,chymreadstaticfields
	open(10,file='../chym/tmp/test.chym',status='old',form='unformatted')
	call chymreadstaticfields(10)
	wkm1=0
	do i=1,mchym(6)
	   call chymreaddynamicfields(10)
	   wkm1=wkm1+rain
	enddo
	rain=wkm1
	call chymplot(6,'Llc2')
	call displayplot(' ','Total accumulated rain',' ')

The following routines are usually automatically called by the previous two and not by the users.

chymheader(iunit)

Read from the logic unit specified by the first argument the header of CHyM output files. Informations are stored in the vectors mchym, rchym and schym defined in the chymdata module.

chymreadpar(iunit,mchym,rchym,schym,ndat)

Read from the logic unit specified by the first argument the header of CHyM output files. The header of such files contains all the information about the run that produced the file. See the description of vectors mchym, rchym and schym in the table below. Please note: in the current version: the integer input parameter ndat must be set to 50, and all the output vectors must be dimensioned 50 as follow:
integer mchym(50) ; real rchym(50) ; character schym(50)*50

chymreadrec(iunit,fld,source,vect,ildate)

Read from the logic unit specified by the first argument the CHyM field specified by the second character argument. The static and dynamical fields saved in the output file are listed in the elements of string vector schym (see the table below). The string output argument source will contain the source of the retrieved array (as an example: "CHyM" or "USGS" etc...), the array vect will contain, as output, the retrieved array, the integer ildate will contain, as output, the coded value of the date.

The following two routines allow to create a netcdf file containing a CHyM field and are available only if netcdf library are available in the used platform

call chym2nchead(ncs,nci,ncr)
call chym2ncfield(field,ncs,nci,ncr)

chym2nchead and chym2ncfield allow to create a netcdf file containing a CHyM field. The first is used to create (or overwrite) the file, the second one is used to add the field time slice(s).
The real array field(nlon,nlat) contains, as input, the field; ncs,nci,ncr are three vectors dimensioned character ncs(10)*32 ; integer nci(10) ; real ncr(10). The meaning of the each component is specified in the following table.

Component	ncs	nci	ncr
1	I/O filename	Number of time slices to write in the nc file	NOT YET USED
2	Short name of the field as an example "rain"	Coded value of first saved time slice; usually CHyM variable: mchym(4)
3	Unit as an example "mm/h"	Number of the current time slice to save (1, 2, ....nci(1))
4	Long name of the field as an example "Precipation field"	Coded value of current time to save, usually the same of CHyM variable: time
5	NOT YET USED	NOT YET USED

The following example shows how to save the precipitation fields from CHyM output

	use chymdata , only : chymreadstaticfields,mchym,temp,time
	integer i,,nci(10) ; real ncr(10) ; character ncs(10)*32
	open(10,file='tmp/oprun03.chym',status='old',form='unformatted')
	call chymreadstaticfields(10)
	ncs(1)='temp.nc' ; ncs(2)='temp' ; ncs(3)='degree (K)' ; ncs(4)='Temperature'
	nci(1)=mchym(6) ; nci(2)=mchym(4)
	call chym2nchead(ncs,nci,ncr)
	do i=1,mchym(6)
	   call chymreaddynamicfields(10)
	   nci(3)=i ; nci(4)=time
	   call chym2ncfield(temp,ncs,nci,ncr)
	enddo
	end

Routine to calculate specific fields

bddfield(thresh)

This routine calculate the bdd matrix from the current value of port array. The threshold value passed as argument represent the minimum value of drained area below which bdd array is set to the special value -9999; if a value lower than zero is passed, this value is calculated as a function of longitude resolution, in this case the threshold will be 25 Km2 for a resolution of 0.006 and will increase or decrease accordingly. An example of how to calculate and plots bdd follows:

	use chymdata , only : chymreadstaticfields
	open(10,file='tmp/oprun03.chym',status='old',form='unformatted')
	call chymreadstaticfields(10)
	call chymreaddynamicfields(10)
	call bddfield(-1.0)
	call chymplotbdd('Lldm0M200c2')
	end

caiindex(flag,thresh)

This routine calculate the CAI alarm index, from the accumulated rain.
Please carrefully consider that the calculated field is stored in the array bdd, and therefore the field previously calculated with bddfield routine IS LOST.

If the integer flag passed as first argument is zero, the array is not calculated, but the rain is accumulated in the appropriate array allocated by caiindex. The CAI alarm index is actually calculated only if the flag is non-zero; note that you may calculate CAI index, in an consistent way, only if you accumulated the rain for a number of hour at least equal to the highest value for average runoff speed for the simulated domain; as an example, if the maximumum value for average runoff speed is 50, you have to call caiindex at least 50 times with flag=0, before to actually calculate CAI index (with flag=1), if this is not the case a warning message is provided by caiindex subroutine.

The threshold value passed in the second argument represents the minimum value of drained area (Km²) below which cai array is set to the special value -9999; if a value lower than zero is passed, the valid range will be between zero and the absolute value of the threshold passed as second argument (this will be a possible application for landslide prediction). An example of how to calculate and plots CAI index follows:

	use chymdata , only : chymreadstaticfields
	areath=25.0
	open(10,file='tmp/oprun03.chym',status='old',form='unformatted')
	call chymreadstaticfields(10)
	do i=1,100
	   call chymreaddynamicfields(10)
	   call caiindex(0,areath)
	enddo
	call caiindex(1,areath)
	call chymplot(29,'Lldc2')
	end

Two examples obtained whit a positive and negative value of area threshold are shown below.

chymrunoffspeed

Calculate the runoff speed and the lenght of river path along each cell (arrays alfa and dx), it is usually called by chymstaticfields that, in turn, is called by the interface chymreadstaticfields.

General pourpose routines for drainage network manipulation

rollingstones2
(inp,fmap,out,nlon,nlat)

This routine allows to calculate the accumulation matrix of an arbitrary field. The input field is passed as first argument (inp) and the output array out is calculated by this subroutine. fmap is an integer array containing for each cell the surface flow direction (1 means North-West, 2 means North, 3 means North-East and so on).
If all the elements of input array inp contains the value 1.0, the output array out will contain, as output, the total number of cells drained by each grid point. If elements of input array inp contains the area of each cell, the output array out will contain, as output, the total area drained by each cell. If the elements of input array inp contains the precipitation of each cell, the output array out will contain, as output, the total precipitation drained by each cell.
All the arrays must be dimensioned (nlon,nlat).

rollingstones
(inp,wk1,wk2,out,fmap,nlon,nlat)

This routine is the older (and less efficient) version of rollingstones2, it is left for backward compatibility only. wk1 and wk2 are 2 work arrays, the other arguments are the same descript in the section about the subroutine rollingstones2.

runofftime(inp,fmap,out,nlon,nlat)

Calculate the total runoff time for each grid point, namely the time that a raindrop will take to runoff until the mouth of the basin, note the mouth must be intended here in the numerical sense, namely it may be a "true" mouth cell draining toward a sea point or a cell in the border of the current simulated domain. The input real array inp must contains the runoff time of the single cell (seconds); the output real array out will contain the results expressed in hours. fmap is an integer input array containing, for each cell, the surface flow direction (1 means North-West, 2 means North, 3 means North-East and so on).

selectbasin(im,jm,wkm1,wkm2)

or the obsolete
basinpaint
(dem,fmap,luse,wkm1,nlon,nlat,im,jm,wkm2)

This routine allows to select a subdomain containing a basin or a part of it. im and jm are the numerical indexes locating the cell of the river mouth; (or any arbitrary point) whose upstream basin must be rebuilt.
wkm1 array will contain, as output, the number of drained cells.
wkm2 array will contain, as output:

the value of dem for the cells belonging to the selected basin
the special value -5 for not drained cells
the special value -10 for other cells

Calling the old version basinpaint, dem, fmap and luse are respectively the dem, flow directions and land use arrays. nlon and nlat specify the number of longitudes and latitudes of each array.

findijonchymgrid(xlat,xlon,i,j)
or the obsolete
locateij
(xla,xlo,slat,slon,dlat,dlon,nlat,nlon,i,j)

findijonchymgrid (locateij) routine allows to locate the indexes (i,j) of the cell corresponding to the (xlat,xlon) values of latitude and longitude. The value -1 is returned for the index i if the point is located outside the domain.
For the old version, the input variables (slat,slon) respectively specify the first value of latitudes and longitudes; the input variables (dlat,dlon) respectively specify the step (difference between two adjacent cells) in latitudes and longitudes; nlon and nlat specify the number of longitudes and latitudes.

chymlocatedn(xlat,xlon,opt,i,j)

chymlocatedn allows to locate the closest point of drainage network for an arbitrary point specified by lat/lon.
The subroutine returns back in the integer arguments i and j the lon/lat indexes of CHyM grid corresponding to the river point closest to thre coordinates xlat and xlon passed as first two arguments. opt is a character string containing any combination of the following characters:

cX To set the search rank to X (range 1-3). The default is that chymlocateriver looks for the river grid point in the closest 8 adjacent cells. If this parameter is set to 2, the 24 adjacent cells are considered; if this parameter is set to 3, the 48 adjacent cells are considered.
mXX To set the minimum value of drained area to XX Km². The default is that chymlocateriver consider a cell of river all those cells draining at least 100 Km²; this option allows to change the value of this threshold.

If a wrong character is passed to the subroutine an error message with all the valid options is displayed.
Other arguments are the same of chymlocatedn

chymlocateriver
(xlat,xlon,lat,lon,dra,nlon,nlat,opt,i,j)

chymlocateriver is a "lower level" routine of the previous one. It is leaved for backward compatibility. The input real arrays lat, lon and dra respectively contains the matrix of latituds, longitudes and drained area of the CHyM domain; nlon and nlat specify the dimension of the arrays, namely the dimension of CHyM grid.

chymsalmone(drai,luse,fmap,nlon,nlat,cut,
ibas,jbas,nsec,isec,jsec,seqi,seqj,nrivp)

chymsalmone routine allows to calculate the path of the segments of drainage network from the array containing the accumulation values of drained area. The first 8 argument are input variables, while the other are output arguments.

Input parameters

drai is the array containing the accumulated drained area
luse is the array containing the land use code
fmap is the array containing the flow direction code
nlon and nlat are the number of longitudes and latitudes for previous arrays array
cut specify the threshold value to discriminate between land and river points (typically 10 Km²)
ibas and jbas are the indexes corresponding to the location of the mouth of the river the user want to rebuilt

Output parameters

nsec is an integer that will be incremented each time the chymsalmone will "encounter" a new tributary
isec and jsec are two integer vectors where the indexes corresponding the new tributaries, encountered by chymsalmone, will be stored
seqi and seqj are two integer vectors where the indexes corresponding to the path of the selected river will be stored (order is from mouth to spring)
nrivp (number of river points) is an integer specifying the numer of points belonging to the river and stored in the seqi and seqj vectors

chymmouths(cut,nsec,isec,jsec)
or
chymmouthsfinder(w,luse,fmap,nlon,nlat,
cut,nsec,isec,jsec)

chymmouthsfinder (old version) or chymmouths (new version) routines allows to locate the mouths of the river for a CHyM domain, the number of mouths will be stored in the nsec integer variable, while the integer vectors isec and jsec will contain the indexes of the mouths. The input real variable cut specify the threshold value to discriminate between land and river points (typically few Km²).
A mouth must be intented in a numerical sense, namely one of the two following condition must be verified:

The grid point drains from its upstream basin at least cut Km² and it drains toward a point belonging to the sea or to a water body
The grid point drains from its upstream basin at least cut Km² and it drains toward a point located on the border of the simulated domain, namely the true mouth is located outside the selected domain.

For the old version, the input array drai contains the accumulation values of drained area, namely each component of drai matrix contains the area of upstream basin for that cell. The arrays luse and fmap respectively contains the land use and the flow direction code. nlon and nlat specify the number of longitudes and latitudes for each array. In the new version routine chymmouths these variables are taken from chymdata module.

chymriverpath(istart,jstart,cut)

chymriverpath is essentially similar (for some point of view identical) to the previous chymsalmone routine, but it is easier to use beacuse it needs only feew arguments.
istart and jstart are the indexes corresponding to the starting point (usually the mouth of the river).
cut is real input parameter specifying the minimum value of drained area (in Km²) to be considered, this parameter is usually few tens of Km², to be more general it is usully calculated as rchym(6)/40.0 being rchym(6) the approximate resolution (meters) for the current domain.
The results of the subroutine are stored in the variables and vectors of chymdata, more specifically:

nrivp will contain as output the number of points belonging to the river path
seqi and seqj are two integer vectors containg the sequence of coordinates for the nrivp points belonging to the river path, the sequence is from mouth to spring

chymmouths(cut,nriv,im,jm)

chymmouths is essentially similar (for some point of view identical) to the previous chymsalmone routine, but it is easier to use beacuse it needs only feew arguments.
cut is real input parameter specifying the minimum value of drained area (in Km²) to be considered, this parameter is usually few tens of Km², to be more general it is usully calculated as rchym(6)/40.0 being rchym(6) the approximate resolution (meters) for the current domain.
nriv is an integer containing, as output, the number of river mouths draining at least the a surface greater than the value specified by cut input variable.
im and jm are two integer vectors containg the longitude and latitude indices of nriv mouths.

Utilities for grid manipulations.

chymdownscaling(tm,xlon,xlat,ixm,jxm
mt,ca,work,nlon,nlat,slon,slat,dij,dji)

chymdownscaling is a general purpose routine to downscale on CHyM grid a field defined on an arbitrary grid. ixm and jxm are the dimension of the input matrix tm while xlon and xlat contain, as input, the latitudes and longitudes of such matrix. nlon and nlat are the dimension of the output matrix mt while slon and slat are respectively the first longitude and latitude of CHyM grid, dij and dji are respectively the resolution of CHyM grid along longitude and latitude. ca and wk are two matrix dimensioned (nlon,nlat) that will be used by chymdownscaling routine to apply Cellular Automata based downscaling; note that this tecnique is generally very timeconsuming if you use it with default parameter (few second per each map to downscale), the number of CA cycles are calculated as 100xR being R the average ratio between input and output grid resolution; you may want to speed up this algorithm setting an adequate value to chymdownscaling cycles MVLib parameter.

chymmoveahead(id,i,j)

Modify the integer arguments i and j with the coordinate of the cell specifyed by the first integer arguments. As an example if, as input, i=20 and j=10 and id=1 this routines gives back i=19 and j=11 namely the indexes corresponding to the closest north-west cell; if id=2 this routines gives back i=20 and j=11 namely the indexes corresponding to the closest cell in the northward direction.

neighborhood(id,di,dj)

Returns, in the integer arguments di and dj the relative coordinates corresponding the idth cell in the neighborhood.
According to the rules used inside CHyM code, the cells of the neighborhood are numbered in a clockwise direction starting from north-west. As an example, if the input is id=1, this routines gives back di=-1 and dj=1 namely the relative cooordinates corresponding to the closest north-west cell; if id=2 this routines gives back di=0 and dj=1 namely the relative cooordinate corresponding to the closest north cell; and so on.
As can be visualized in the first picture, the cells of each frame are numbered in a clockwise direction starting from north-west grid point: the second frame starts from 9, the third frame starts from 25 and so on.
In the corrent version, the subroutine is conventionally limited to 40 frames (only the first 6 are shown in the fugures below), and then the input parameters of this routine can be in the range 0-6560.
The second and third picture shows the output values corresponding to different input value.

withinrange(val,left,right)

withinrange is an integer function returning 1 or 0 depending whether or not the first value passed as argument is included between the interval specified by the other two argments, as an example withinrange(5,3,10) returns 1 and withinrange(5.0,13.5,20.0) returns 0. Note that this function is actually an interface accepting all real arguments or all integer arguments and therefore it must be declared where used.

	use chymdata , only : withinrange

MVLib-CHyM variables exchange (Usually NOT called by the users)

chymdomain(nlon,nlat,
zoom,lon1,lon2,lat1,lat2)

Allows to define the boundaries for the next CHyM 2-dim plot. The first three integer arguments respectively specify the number of longitudes, the number of latitudes and the zoom flag. If zoom is not zero the for integer parameters lon1, lon2, lat1 and lat2 specify the range of lat/lon indexes to be plotted. This routine is usually called by chym2mvlib or chymgrid

chym2mvlib(mchym,rchym,schym)

It is used (usually by chymreadpar routine) to pass to MVLib libraries the parameters of "current" CHyM run.

chymgetrpar(i,r)

Return in the second real argument the ith component of CHyM real parameter, as an example if the first argument is equal 2, the first value of latitude for the selected domain is returned in the second argument.

chymgetipar(i,r)

Return in the second integer argument the ith component of CHyM integer parameter, as an example if the first argument is equal 2, the number of longitudes for the selected domain is returned in the second argument.

chymgetcpar(i,r)

Return in the second character argument the ith component of CHyM character parameter, as an example if the first argument is equal 6, the title of the simulation is returned in the second argument.

chymgrid(nlon,nlat,slon,slat,dij,dji)

Same pourpose as chym2mvlib, but in this case only the parameters needed to define the CHyM grid are passed to MVLib libraries.

getchymgrid(nlon,nlat,slon,slat,dij,dji)

opposite function of chymgrid, in this case the variable stored in MVLib internal vectors are retrieved.

chymsavedfield(fld)

chymsavedfield is logical function returning true if the string passed as argument is saved in the current output file. It must be called after read the CHyM output file header or after call chym2mvlib routine.

chymrivername(lat,lon,river)

Returns in the character variable river, the name of the river whose mouth is located in the coordinates specified by the first two real arguments. The river name must be defined in the museo database and the lat-lon must be located at less than one chilometer respect to data saved in museo database. If the river is not find, the string "Unknown" is returned in the river variable.

chymstdomain(idom)

Define standard CHyM domain for graphic routines, if the integer argument is 21, parameters for Acqwa project Po basin are defined; with this flag set to 22 the parameters for Acqwa project Rhone basin are defined.

Subroutines to access temperature and precipitation data in a suitable form for CHyM model.

acqwascen01
(hour,day,month,year,flag,vec,lat,lon,n)

Allow to rertrieve the precipitation (flag=1) and temperature (flag=2) for Acqwa project 01 scenario, namley the Post processed RCM-REMO, 25x25 km, 3 hours of time resolution. The data are stored in the output real vectors vec, lat and lon (sontaining respectively temperature or precipitation, latitudes and longitudes), the last argument is the number of data available and the first four integer input arguments specify the time step. Note that, for temperature data, it is returned n=0 if the routine is called two (or more) consecutive times with the same 3 hours-step, this is done to speed-up the execution of the model, because, in this case, CHyM will use the same temperature field of the previous step. See here the complete description of Acqwa project scenarios.

acqwascen02
acqwascen03
acqwascen04
acqwascen5a
acqwascen5b
acqwascen6a
acqwascen6b
(hour,day,month,year,flag,vec,lat,lot,n)

Same as acqwascen01 but for Acqwa 02, 03, 04, 5a, 5b, 6a and 6b scenarios. See here the complete description of ACQWA project scenarios.

Graphic routines

chymplot(flag,opt)

chymplot is an high level routine allowing to produce the standard plots of chym fields. The first argument is an integer flag specifying the field to be plotted. For each plot the data currently stored in the chymdata module is used, as a consequence to plot CHyM fields is usually very simple. As an example to produce the plot of DEM require a three-line program looking as follow:

	use chymdata , only : chymreadstaticfields
	call chymreadstaticfields('tmp/Po.chym',0)
	call chymplot(1,'dLl')

For each value of the first integer flag, the following plot are produced:

01 Digital Elevation Model
02 Land Use Map
03 Flow Direction Map
06 Precipitation Map
10 Precipitation Source Code Map
13 Temperature Map
21 Surface runoff speed
22 Runoff time on the single grid point
23 Average runoff time
24 Number of drained cells
25 Average runoff time for the upstream basin
26 ModIS snow cover map
28 BDD alarm index map
29 CAI alarm index map

The meanings of the options are the same described for chymplottemp routine described below.

chymplottemp(temp,nlon,nlat,opt)

Plot the temperature field contained in the real array temp; nlon and nlat specify the number of longitudes and latitudes for this array. opt is a character string containing any combination of the following characters:

a To avoid the automatic setting of window frame. The plot is produced with current settings allowing, as an example, to produce several plots on the same figure. See example 45.
d To activate the display of the plot
l To activate the display of the label bar
L To activate the the tracking of lat/lon lines
cXX To set the boundary flag to XX (range 1-9), if XX is omitted or a wrong value is passed, the routine will draw provinces boundaries for Italy and political boundaries for the rest of the world
mXX To set the minimum value of plot to XX, if the minimum is not specified it will be set as the minimum value of the input array passed as first argument
MXX To set the maximum value of plot to XX, if the maximum is not specified it will be set as the maximum value of the input array passed as first argument

If a wrong character is passed to the subroutine an error message containing all the valid options is displayed.
chymplottemp is actually a general purpose routine to display most of CHyM fields; in fact chymplot described above is just an higher level interdace to this routine.

chymplotdiff(diff,nlon,nlat,opt)

Plot the difference field contained in the real array diff; nlon and nlat specify the number of longitudes and latitudes for this array. opt is a character string containing any combination of the following characters:

a To avoid the automatic setting of window frame. The plot is produced with current settings allowing, as an example, to produce several plots on the same figure. See also the example 45 to understand the details.
d To activate the display of the plot
l To activate the display of the label bar
L To activate the the tracking of lat/lon lines
cXX To set the boundary flag to XX (range 1-9), if XX is omitted or a wrong value is passed, the routine will draw provinces boundaries for Italy and political boundaries for the rest of the wordl
MXX To set the maximum value of plot to XX, if the maximum is not specified it will be set as the maximum value of the input array passed as first argument. The minimum value is alway set to minus the maximum value.
r To reverse the color bar, by default the color bar are from blu to red tones
Txx To set the style of the plot to the value XX, valid ragnges are 0-4 and 10-14. If this parameter is greater than 10 the label bar is produced under the current frame, instead at bottom of the plot. If you pass T0 (default) the whole palette is used (10 or 15 if r is specified); if you pass T1 only three colours are used; a colour for the values less than -max, a colour for the values greater than max, and a colour for other values. If you pass T2 subset of 16 colours are used centered around the zero; if you pass T3 a subset of 9 colours are used centered around the zero; if you pass T4 a subset of 5 colours are used centered around the zero. See the example 45 to better understand the differences.