Preparing CMOR for
CMIP6 and other WCRP Projects
Charles Doutriaux and Karl E. Taylor
Presented at the
4th Annual ESGF & UV-CDAT Meeting
Livermore, CA
11 December 2014
Outline
•
What is CMOR (the Climate Model Output Rewriter)?
•
What changes are planned?
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
Why CMOR?
•
PCMDI and now WCRP advocate adoption of common
standards/conventions for the:
•

Structure and format of climate data

Metadata used to describe climate data

Vocabulary used for categorizing the diversity of model output
Standardization enables/facilitates


Automation in the preparation of model output
Analysis by researchers using uniform methods for reading and interpreting
data

unique identification of files

sharing of data across the ESGF network
•
But model output stored in native formats following a diversity of
approaches must be “translated” into the standard form
•
CMOR was written to facilitate this.
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
What is CMOR?
•
CMOR is a library of C functions which facilitate/enforce
compliance with MIP requirements.

Includes interface to both Fortran and python code
•
CMOR was designed to be adapted to the different
metadata requirements of each “model intercomparison
project” (e.g., CFMIP, HTAP, PMIP)
•
Most of the CMIP3 and CMIP5 output served by ESGF was
processed through CMOR.

CMOR has been key to ensuring uniformity across all models
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
Project-specific CMOR tables facilitate and ensure
consistency of model output from contributing groups
•
•
Proper specification of coordinate and variable attributes,
including:

Correct standard names and units

Use of a common time coordinate model (with flexibility)

Required dimensions (but with different grids allowed)
A capability to

Reorder axis order

Reverse axis direction (or translate longitude dimension)

Convert units (through udunits)
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
What standards does CMOR ensure compliance with?
•
netCDF – (www.unidata.ucar.edu/software/netcdf/)
•
CF Conventions – provides for standardized description of
data contained in a file (cf-convention.github.io)
•
Data Reference Syntax (DRS) – defines vocabulary used in
uniquely identifying MIP datasets and specifying file and
directory names (cmip-pcmdi.llnl.gov/cmip5/output_req.html).
•
CMIP output requirements – specify the data structure and
metadata requirements for CMIP data (cmippcmdi.llnl.gov/cmip5/output_req.html)
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
CMOR flags common errors, including
•
Pointing out when required metadata are omitted.
•
Rejecting incorrect metadata (wrong units, inadmissible
attribute values, etc.)
•
Rejecting inconsistent coordinate dimensions passed by
user to CMOR.
•
Rejecting non-monotonic coordinate values or inconsistent
boundary values, as passed by user.
•
Rejecting values that are clearly unrealistic (likely
indicating improper units conversion or incorrect sign).
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
CMOR history
•
•
Original CMOR used in CMIP3

Written in FORTRAN 95.

accommodated only data stored on cartesian longitude-latitude grids.
CMOR-2 used in CMIP5

CMOR’s structure and functions were largely unchanged.

Written in C (with FORTRAN 95 and python interfaces)




Can write output on model “native” grids that are not cartesian
longitude-latitude.
Station data (needed, for example, by the HTAP project), including
metadata for station names and station locations
Regional model output handled smoothly.
Relies on netCDF-4 (rather than NetCDF-3), which provides for
automated compression.
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
What is planned for CMOR-3?
•
Generalization to better handle a wider range of model
output and observational data.



•
CMOR was developed (and to a certain extent “hard-wired” to meet
modeling needs
Some of the attributes written by CMOR don’t apply to observations
(e.g., model name, experiment name)
Modifications are needed to simplify the reconfiguration of the input
tables for each new MIP.
Modularization of the CMOR input tables, separating

Project-specific metadata from

Variable information
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
What needs to be done for CMIP6?
•
Write and release CMOR-3
•
Generate new CMOR tables

Allowing additional required global attributes? (e.g., version info.)

Recognizing CMIP6 controlled vocabulary

Including any new requested variables.
•
Provide more complete QC information to CMOR (e.g., valid
max and min for each field)
•
Modularize the CMOR input tables to separately specify

Project-specific information

List of variables and their metadata
ESGF F2F
11 December 2014
K. E. Taylor
PCMDI
For further information: https://github.com/PCMDI/cmor
Documentation
ESGF F2F
11 December 2014
Issues
K. E. Taylor
PCMDI