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
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