[CF-metadata] attributes for min/max data values for?visualization

[Jonathan Gregory]

Dear Steve

Your idea could actually be done more simply using the existing conventions
for cell_methods. For instance, the maximum over all levels, and the maximum
as a function of level, would be

variables:
  float temperature(time,pres,lat,lon) ;
    temperature:standard_name="air_temperature";
  float temp_max_of_pres(pres) ;
    temp_max_of_pres:cell_methods="time1: lat1: lon1: maximum";
    temp_max_of_pres:coordinates="time1 lat1 lon1";
    temp_max_of_pres:standard_name="air_temperature";
  float temp_max_overall;
    temp_max_overall:cell_methods="time1: pres1: lat1: lon1: maximum";
    temp_max_overall:coordinates="time1 pres1 lat1 lon1";
    temp_max_overall:standard_name="air_temperature";

where the names ending in -1 are scalar coordinate variables. They could
equivalently be size-one 1D coordinate variables, in which case we would have
temp_max_of_pres(time1,pres,lat1,lon1)
temp_max_overall(time1,pres1,lat1,lon1)
In either case, their purpose is to record the bounds of the original
coordinate range over which the maximum was calculated.

Cheers

Jonathan