Recommendation:

We recommend that datasets in grid structures include a Time dimension, even if Time is degenerate (i.e., includes only one value) for the cases when the entire grid has one time range or time stamp.

Recommendation Details: A Time dimension is required for a single grid product file that contains many time intervals of daily, weekly, or monthly averages. In contrast, grid product files that are distributed as daily, weekly, or monthly granules that have one time range or stamp for the entire grid could be defined without a Time dimension because each file records the specific time interval being provided in both the file name and file-level attributes. We nevertheless recommend that a Time dimension be defined and used in all data fields that vary in time, regardless of whether multiple time slices are stored in the file. More specifically, we recommend that Time be defined as a record dimension, not a fixed-length dimension. This allows downstream users to more easily and efficiently aggregate data across separate files because HDF5 and netCDF4 storage geometries and APIs are designed to more easily extend record dimensions than fixed-length dimensions.

Unfortunately not all software understands multi-dimensional datasets with Time as one dimension. In such situations, the NCO ncwa operator can be used to eliminate the Time dimension from an entire file with a single command.