CMIP7 Global Attributes, DRS, Filenames, Directory Structure, and CVs

Summary

In files containing CMIP model-simulation output, global attributes are used to describe the source of the data, the imposed experiment conditions, the contents of the file, licensing restrictions, and other information useful to those analysing the data. Here we define the global attributes that should appear in CMIP7 files (some are required, others optional), along with the so-called CMIP7 “data reference syntax” (DRS) used to uniquely define datasets. The subset of global attributes that defines the DRS is used in constructing the directory structure and file names found in the CMIP7 archive, and also can be used, for example, in populating search facets.

Introduction

As in earlier phases of CMIP, a well-defined set of global attributes will be recorded in each CMIP7 model output file, providing information necessary for interpreting the data. Table 1 contains the list of CMIP7 global attributes and indicates which ones are required and which are optional. The values for many of the global attributes must be drawn from special CMIP7 “controlled vocabulary” (CV) lists of terms. A CV, in simplest form, is a list of the permitted values that can be assigned to a given global attribute. Some of these lists appear in this document, but they should not be relied on to be 100% correct. Rather, consult the reference CVs for CMIP7, which should become available at https://github.com/WCRP-CMIP/CMIP7-CVs/.

Documents of related interest may be found at https://wcrp-cmip.github.io/cmip7-guidance/, which will be updated as more guidance documents are created.  Of particular relevance is https://wcrp-cmip.github.io/cmip7-guidance/docs/CMIP7/Global_Attributes/   which includes  much of the same information provided by this document but supplements it with an indication of how the global attribute requirements differ from CMIP6 and describes more completely the data reference syntax (DRS).