Format for Transmitting Model Output to PIRCS(1c) Archive

Model output should be transmitted to PIRCS in one of two formats, either NetCDF format or the format used in PIRCS(1a) and PIRCS(1b). Model output submitted in PIRCS format must include one ASCII file containing information for reading output. For model output submitted as NetCDF data, we request that all model parameters (grid spacing, number of vertical levels, base state pressure, etc.) are included in the NetCDF files and that a sample program to read the NetCDF files is provided.

For those who wish to submit data in PIRCS(1a) and PIRCS(1b) format, please use exactly the same routines without corrections to any errors that may have been discovered since the last data transmission. Our code is designed to read the quirky rather than corrected data files. Also, note that the file naming convention has changed (see "NetCDF Files" below), and that PIRCS no longer requests output on the native model levels; instead submit data on the following pressure levels: 925, 850, 700, 500, and 200 mb. The PIRCS output files require a field ID number, available in Table 1. A table of representative values is available for guidance when preparing output for the archive. Please adhere carefully to the units assigned each variable in these tables!


The ASCII file provides general information to identify the model and gives control data for reading the output. It also has some redundancy with the output to help maintain proper identity of the output files.

The file should be named IDDDDD.CONTROL, where IDDDDD is the 6-character identifier string in line 1 below.

The file should contain at a minimum 6 lines:

Line Information
1 A model ID (character variable; A6 format). This ID should be the prefix to all files sent to the PIRCS archive (see "File naming convention" under NETCDF FILES, section 3(a))
2 Start day (3 integers in year, month, day order in I5 format; 4-digit year that includes century, i.e. 1988 not 88)
3 End day (3 integers in year, month, day order in I5 format; 4-digit year)
4 Number of "latitudes" (gridpoints in y-direction of model output grid; 1 integer in I5 format)
5 Number of "longitudes" (gridpoints in x-direction of model output grid; 1 integer in I5 format)
6 Byte-order indicator (character variable; A6 format). Enter "BIG..." or "LITTLE" to indicate whether your machine uses "big endian" or "little-endian" byte order for floating-point numbers. Consult your system's 'man' pages or other documentation to find which ordering it uses.
7-10 The file may contain up to 4 additional lines, 80 characters wide, of additional comments.


1. General structure

Output should be stratified as follows, with "Date/time" representing the coarsest division of the output and "Longitude" representing the finest.

Date/time	<- coarsest
Longitude	<- finest

The terms "latitude" and "longitude" are used loosely in this document to refer to the model's Y and X coordinates, respectively, where Y increases approximately from south to north and X increases approximately from west to east. It is not necessarily implied that the data should be interpolated to an actual latitude-longitude grid.

2. Order

Output and related reference fields are to be reported in the order given on the PIRCS(1c) web page tables:

Table 1

3. Files

File naming conventions and content depend on whether the data is submitted in PIRCS or NetCDF format. We recommend creating monthly files if data is submitted in PIRCS format and daily files if NetCDF format is used.

(a1) File naming convention (monthly files): IDDDDD.FIELD.YYYY.MM.DD.YYYY.MM.DD

An example of a properly constructed file name is: NCPRSM.6HGEOP.1987.07.01.1987.07.31

(a2) File naming convention (daily files): IDDDDD.FIELD.YYYY.MM.DD

An example of a properly constructed file name is: NCPRSM.1987.07.01

(b) For PIRCS format data files, output should be written as one file per output field per month unless the file size would exceed 2 Gb. Data submitted in NetCDF format may contain multiple variables, but please adhere to the 2 Gb file size limit. We suggest constructing daily output files and making monthly tar archives.

(c) For min/max temperatures, report the times of minimum and times of maximum in separate files from the actual values of minimum or maximum temperatures.

4. Horizontal grid

(a) All requested fields should be reported on the same horizontal grid. For models that stagger variables horizontally, output should be interpolated horizontally to a common grid. When interpolation is needed, it is recommended that wind fields be interpolated to the grid used for mass and temperature variables.

(b) When writing two-dimensional (horizontal) fields:

  1. Start in the southwest corner and proceed "eastward" in model's x direction
  2. Increment latitude from south to north, always writing from the latitude's westernmost point toward the easternmost.

(c) When writing three-dimensional fields:

  1. Write output as a sequence of two-dimensional (horizontal) fields.
  2. Start with atmospheric layer closest to surface.
  3. Proceed upward to layer farthest from surface.

5. Vertical grid

(a) All requested three-dimensional fields should be reported at the following pressure levels:

925 mb, 850 mb, 700 mb, 500 mb, and 200 mb

(b) When writing fields, go from the lowest layer of the model atmosphere toward the top of the model atmosphere.

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