Advanced Scientific Computing Research (ASCR) under the U.S. Department of Energy Office of Science (Office of Science)

Project Team Members:

Northwestern University

The HDF Group

Argonne National Laboratory

North Carolina State University

Northwestern University - EECS Dept.

Data model for Community Atmosphere Model (CAM)

This is based on a datafile from Rob Jacob (ANL), generated by CAM.

Note, in the description below, for dimension "dim", number of values given for dim is denoted as #dim. Also, values for a vector, e.g. for x, are given as e.g. "x[] = lat[IMIN..IMAX-1],lat[IMAX]=lat[IMAX-1]+dx, meaning that x has the same values as lat for the first IMAX-IMIN values, then for the last value it is lat[IMAX-1]+dx.

The numbers of the major sections correspond to those given in the description in DataModel. The fact that they appear out of order means that maybe we should change the order in which the various sections in the data model are described.

The header information from original data file is attached (scroll down to bottom for link).


  1. lat/64 --> dimensions handle hd1
  2. lon/128 --> dimensions handle hd2
  3. lev/26 --> dimensions handle hd3
  4. ilev/27 --> dimensions handle hd4
  5. isccp_prs/7 --> dimensions handle hd5
  6. isccp_tau/7 --> dimensions handle hd6
  7. isccp_prstau/49 --> dimensions handle hd7
  8. time/UNLIMITED) --> dimensions handle hd8
  9. tbnd/2 --> dimensions handle hd9
  10. chars/8 --> dimensions handle hd10

Dimensions values: vectors of data, one per dimension, 1d array of dimension length.


  1. lat: degrees_north --> units handle hu1
  2. lon: degrees_east --> units handle hu2
  3. lev, ilev: level --> units handle hu3
  4. isccp_prs: mb (milibars) --> units handle hu4
  5. isccp_tau: (none) --> units handle hu5
  6. isccp_prstau: mb/1000 --> units handle hu6
  7. time, tbnd: days since 0000-09-01 00:00:00 --> units handle hu7
  8. pressure: Pa --> units handle hu8
  9. seconds: s --> units handle hu9 ( note 4)
  10. fraction: f --> units handle hu10
  11. massflux: mflux (kg/1/0, m/0/2, s/0/1) --> units handle-- --hu11

Structured vertex block:

IMIN/IMAX=0/#lat; JMIN/JMAX=0/#lon; KMIN/KMAX=0/#ilev-1;
x[] = lat[IMIN..IMAX-1],lat[IMAX]=lat[IMAX-1]+dx
y[] = lon[JMIN..JMAX-1],lon[JMAX]=lon[JMAX-1]+dy
z[] = ilev[KMIN..KMAX-1]
periodic = [true, true, false]

--> block b1, start handle hx1

Structured hex block:

IMIN/IMAX=0/#lat-1; JMIN/JMAX=0/#lon-1; KMIN/KMAX=0/#lev-1
Uses block b1

--> block b2, start handle he1


Note, I only define one of the variables for each given type (there are a total of 128 in the file). In the table, so(x) denotes sizeof(type x), while #y means # values in dimension y

Name size type size data type def val storage type units Tag(value)
long_name var -- opaque -- sparse -- --
cell_meth var -- opaque -- sparse -- --
P0 fixed so(dbl) dbl -1.0 dense hu8 long_name(reference_pressure)
date_wrtn fixed #chars int -1 sparse --
mdt fixed so(int) int -1 sparse hu9 long_name(timestep)
nlon fixed #lat int -1 sparse -- long_name(number of longitudes)
ndcur fixed #time int -1 sparse hu7 long_name(current day (since base day))
CLDHGH fixed #time dbl -1.0 dense hu10 long_name(Vertically-integrated high cloud", cell_meth("time:mean")
CMFMC fixed d(time) dbl -1.0 dense hu11 long_name(Moist shallow convection mass flux), cell_meth("time:mean")
source var -- opaque -- sparse --

Tag values: The following describes which entity(ies) each of the above tags is applied to; again, only a representative set are described,

Tag Entity(ies) # values/entity notes
P0, date_wrtn, mdt Interface 1 global variables, scalars
nlon Interface #lat global attributes, 1D vector with dimension fixed
ndcur Interface #time global variable, 1D vector with unlimited dimension
CLDHGH quads q(lat,lon) bounding hexes hex(0,lat,lon) #time 1D vector with unlimited dimension
CMFMC vertices v(ilev,lat,lon) #time 1D vector with unlimited dimension
source Interface 1 global attribute
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Last Updated: $LastChangedDate: 2016-11-06 13:53:06 -0600 (Sun, 06 Nov 2016) $