Dear all Heinke Hoeck, Alison Pamment and I have had a long debate on the email list, and more recently in trac ticket 33 http://cf-pcmdi.llnl.gov/trac/ticket/33, about the metadata needed to describe quantities which relate to the number of occurrences and the spell-length of extreme events. Heinke and I have developed a proposal which involves using cell_methods and is illustrated by an example to be added to the conventions. The main part of the proposal is for some new kinds of standard name, as follows:
A variable whose standard name has the form number_of_days_with_X_below|above_threshold must have a coordinate variable or scalar coordinate variable with the a standard name of X to supply the threshold(s). It must have a climatological time variable, and a cell_methods entry for "within days" which describes the processing of quantity X before the threshold is applied. A number_of_days is an extensive quantity in time, and the cell_methods entry for over days should be "sum". A variable whose standard name has the form spell_length_of_days_with_X_below|above_threshold must have a coordinate variable or scalar coordinate variable with the a standard name of X to supply the threshold(s). It must have a climatological time variable, and a cell_method entry for "within days" which describes the processing of quantity X before the threshold is applied. A spell_length_of_days is an intensive quantity in time, and the cell_methods entry for over days can be any of the methods listed in Appendix E appropriate for intensive quantities e.g. "maximum", "minimum" or "mean". Both kinds of quantity are dimensionless (they are counts). We propose to add these definitions to the standard_name guidelines. They would fit in the "Transformations" section. The following new standard names are proposed now, following these patterns: number_of_days_with_air_temperature_below_threshold number_of_days_with_air_temperature_above_threshold number_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold number_of_days_with_wind_speed_above_threshold spell_length_of_days_with_air_temperature_below_threshold spell_length_of_days_with_air_temperature_above_threshold spell_length_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold spell_length_of_days_with_lwe_thickness_of_precipitation_amount_below_threshold This proposal has received some support in trac. As I said, it is the outcome of a long discussion, which can be found in the email list archives. Cheers Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
