General Conventions approved by NUWG Variables --------- The variable names chosen for netCDF variables will be up the supplier of the data set. The agreement by this group is that all code written to read netCDF data will NOT be variable name dependent. Code will be written generically using the netCDF inquire functions or will employ some sort of table look-up algorithm. Attributes ---------- The group has agreed to attach "long_name" attributes to all variables as a means of self-documenting files. When a user performs an ncdump, "long_name" attributes should help that user understand what is contained in the file. Any units used must be compatible with the UDUNITS library and consistent for a given variable (For example, a data supplier chooses to store SAO temperatures as degrees C. The supplier will convert all U.S. temperatures reported in degrees F to degrees C). The "units" attribute is required for all measured or observed variables on which programs might perform numerical computations. Time Representation ------------------- The NUWG agreed that all time fields will be represented such to be compatible with the UDUNITS library. We agreed that time should be represented as a double such as: double time :units = :long_name = :_FillValue = Defining time as a double gives the most flexibility to the widest range of data sets. Station Identification ---------------------- To identify fixed location stations, we agreed that the numeric WMO id would be the identifier of choice. As mentioned above, data suppliers could add an internal id in addition to the WMO id. To fully identify stations, a station name, the latitude, longitude and elevation of the station will be required. General Comments ---------------- In general, the netCDF definitions for a data set that we create are considered a minimum set of variables for data exchange. The data provider is free to add additional fields as needed for quality control, further identification, or other internal uses. ------------------------------------------------------------------------------- by Susan Jesuroga jesuroga@comet.ucar.edu for NUWG nuwg@comet.ucar.edu Updated October 5, 1993