Dear Dan Yes, I see what you mean regarding the aux coord, and it's a neat idea, but it doesn't seem quite right to me. Aux coords are alternative or additional information. The lat(x,y) and lon(x,y) coordinates provide an alternative way to locate the point (x,y), in a different coordinate system. The precipitation probability, however, would determine the precipitation entirely. There isn't any coordinate information which would give you the precipitation amount. That is why I don't think the probability can be an aux coord. Does that make sense?
> You are right regarding the calculation - we are using a statistical model of > the relationship between monthly rainfall and return period that was > developed many years ago by a colleague from an analysis of 60 years of > historical data. The model uses values of the coefficients of variation and > skewness to describe the distribution of monthly rainfall (assumed to be > log-normal). To capture how the shape of the distribution varies with > location we have pre-calculated values of these coefficients available at > each point on a 5 km grid. Right. So it is reasonable to describe it as a conversion of precipitation amount to probability, I think. > If a new standard name is required then I'm happy to take your advice on a > suitable choice. It would be useful to know if anyone else reading this has a view on my suggestion of precipitation_amount_converted_to_cumulative_probability. > What is still not clear to me is how I maintain a clear link between the two > fields without storing some of the information twice. Is it simply a case of > storing two variables in the same NetCDF file (so that they share > coordinates)? If they are in the same file, indeed it is obvious if the fields have the same spatiotemporal coordinates, because they share the coord vars, as you say. If they are in different files, the data-user has to check whether the coords are the same. There is no convention which would allow one to be sure about that without checking. CF does not rely on variable names, for instance. This is a very common situation, in fact. For instance, in the CMIP archives each quantity is in a separate file, and the data variables in many files typically have the same spatiotemporal coordinates, but analysis software cannot be sure of that without checking. Best wishes Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
