[CF-metadata] new standard names: day, night, and day/night terminator area_fractions

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 10 Jan 2014 11:50:36 +0000

Dear Randy

Thanks for this useful summary.

You favour

> (3) make use of existing area_fraction names and qualify the type of area_fraction with one or more coordinate variable(s) and accompany use of cell_methods attribute
>
> pros: no need for an additional standard name, unambiguous, flexible (allows for a variety of yet-to-be-defined quantities), one variable can hold all three values
> cons: modification to the definition of area_fraction required, more complex than other options
> Later comment:
> Option (3) requires separate variables for day, night, and terminator region because a variable has a single cell_methods attribute, and cell_methods is used to specify the areal extent.

I don't think so, actually. cell_methods would have "area: mean" in this case,
I think, because you can consider the area_fraction to be the mean over the
cell of a binary variable (0 or 1). I'm not sure if that's best, but it is
definitely not "point", and "sum" isn't appropriate because it's not extensive.
The bounds would belong to the coordinate variable of solar_zenith_angle.

I would be content with (3) but on the whole I prefer

> (4) a hybrid of (1) and (2) (i.e. area_fraction_of_night_defined_by_solar_zenith_angle, area_fraction_of_day_defined_by_solar_zenith_angle, area_fraction_of_terminator_region_defined_by_solar_zenith_angle)
>
> pros: very clear
> cons: new form of standard names containing area_fraction, 3 standard names where 1 can be made to work

I like this because it's very clear, as you say. It thus avoids the problem of

> (1) add a type of area fraction consistent with current definition of existing area_fraction (i.e.. day_area_fracton, night_area_fraction, day_night_terminator_area_fraction)
>
> pros: clear, consistent with current use and definition of area
> cons: 3 standard names where 1 can be made to work

which doesn't point out so prominently that "day" and "night" have to be
given precise definitions. The discussion shows that (2) causes problems
because we can't find a form of words (so far) that everyone considers to
convey the right notion.

> (2) add a new grammatical form of a standard_name containing area_fraction i.e.. area_fraction_X_solar_zenith_angle, area_fraction_for_solar_zenith_angle_within_bounds)
>
> A variety of options have been set forth for X, such as "of", "as a function of", "with", "defined_by", "with_given"
>
> pros: one standard name, one variable can hold all three values
> cons: new form of standard names containing area_fraction, options are either not particularly clear or violate (to varying degrees) conventions associated with existing standard names,

I'd be interested to know whether you consider "twilight" to be acceptable.
Wikipedia also gives "twilight zone" as a synonym for "terminator". I think
"twilight" goes better with "day" and "night" than "terminator" does.

What do other people think about all the above?

Best wishes

Jonathan
Received on Fri Jan 10 2014 - 04:50:36 GMT