A use case for cell_methods involving climatology: We have an archive of regional climate model outputs. To improve their usability for impacts users, we generate various aggregations at different frequencies. We provide daily, monthly, and seasonal timeseries data, as well as monthly and seasonal climatology data.
(To be explicit: a ten-year monthly timeseries file would contain 120 timesteps, one value for each month in sequential order; a ten-year monthly climatology file would contain 12 timesteps, each an average of the values for that month over all ten years.) The workflow for generating these files is chained. To generate a monthly climatology, we first calculate a monthly average timeseries from a daily timeseries by averaging together daily values for each month, then calculate a monthly climatology by averaging together monthly values across multiple years. If the data variable is something like tasmin or tasmax (daily minimum or maximum temperature), some models will output that directly, but in other cases we may need to calculate it from hourly values. The cell_methods attribute for tasmax monthly climatology thus ends up looking like this: ` tasmax:cell_methods = "time: maximum time: mean time: mean within years time: mean over years" ;` As best I understand the spec, this is completely CF-compliant and correct, although it requires some human interpretation to understand that it means we started with daily maximum values, averaged them to monthly values, then averaged those to monthly climatology. The optional `(interval: )` construct adds some information that could clarify that to a degree (although it would arguably be more useful to have the ending interval than the starting interval, or better yet both), but we don't use it because we are automating this workflow across a very large number of files, the tools we use are generic, and we found that it was too hard to programmatically determine the starting frequency; we ended up with a lot of mangled cell_methods when we tried. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/197#issuecomment-646288026 This list forwards relevant notifications from Github. It is distinct from [email protected], although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to [email protected].
