Order of dimensions for ensemble model output

[knutfrode]

As far as I can understand, CF-convention has no restrictions on the order of dimensions, but recommends using the order
(time, depth/height/z, y, x)

But is there a recommendation/requirement for the order of the additional ensemble/realization dimension for output from ensemble ocean or atmospheric models?
E.g. (ensemble_number, time, depth/height/z, y, x) or (time, depth/height/z, ensemble_number, y, x) ?

[davidhassell]

Hello @knutfrode,

I don't know of any such recommendation or requirement, but I personally would go for (ensemble_number, time, depth/height/z, y, x) on the grounds that, depending on your access patterns, netCDF may be faster when the dimensions are ordered from slowest moving to fastest moving, left to right.

[sethmcg]

There is such a recommendation in the second paragraph of section 2.4. "All other dimensions should, whenever possible, be placed to the left of the spatiotemporal dimensions." This is in accordance with the COARDS recommendation for ordering of additional dimensions.