Dear Jonathan
First of all, regarding propositions for new standard names: It is likely that as a result of this discussion, I will propose some new standard names and name modifiers. But please don't consider any of my ideas here as formal standards propositions.
Now, regarding probabilities of values within a given range:
When we say precipitation_probability we really mean
probability that each value will be within an absolute range given in variable x.
And when we say air_temperature_confidence we really mean
probability that each value will be within a range given in variable x, relative to an air_temperature variable.
These are two very different things, and I believe that they should be treated as such.
For air temperature, I believe that using bounds is not the way to go. There must be some kind of link to the reported temperature. Therefore, I believe that a variable air_temperature confidence with an extra dimension interval_of_air_temperature is better.
Regarding precipitation, bounds seem to do better. But I am not happy about the fact that there must be an artificial upper boundary for precipitation. Also, I am not sure if bounds are intended to be used with overlapping ranges?
I am uncertain about what is best then ? to use bounds with very high upper limit, or to use my original approach ? to create a new standard_name: limit_of_precipitation_amount, and use it as a dimension to precipitation_amount confidence.
Any further thoughts?
-- Vegard
----- Original Message -----
Fra: "Jonathan Gregory" <j.m.gregory at reading.ac.uk>
Til: cf-metadata at cgd.ucar.edu
Sendt: 2. desember 2011 11:10:20
Emne: Re: [CF-metadata] standards for probabilities
Dear Vegard
> A dimension (and variable) for specifying percentiles:
> float percentile(percentile) ;
> percentile:units = "1" ;
> percentile:standard_name = "cumulative_distribution_function" ;
> float air_temperature_percentiles(time, percentile, latitude, longitude) ;
> air_temperature_percentiles:units = "K" ;
> air_temperature_percentiles:standard_name = "air_temperature" ;
This looks sensible to me. Are you proposing cumulative_distribution_function
as a new standard name?
> ...an alternative for percentile could be cumulative_distribution_function_over_realization.
Yes. That would be more informative, and therefore preferable, I think.
> Then, there is the problem of certainty that a temperature will be within a given range.
Could you do that like this:
float air_temperature(air_temperature);
air_temperature:bounds="air_temperature_bounds";
air_temperature:units="K";
float air_temperature_bounds(air_temperature,2);
float air_temperature_confidence(time,air_temperature,latitude,longitude);
air_temperature_confidence:standard_name="probability";
Then the air_temperature_bounds specify the ranges of air temperature for
which the probability is evaluated. probability would be a new standard name
as well. Again it could be made more informative as something like
probability_over_realization. This is instead of a standard_name modifier
and seems more consistent to me with the treatment of percentile. It is a
kind of transpose.
> Also, which I did not mention in the previous emails, I also wanted to express the probability of at least x mm of precipitation.
This can be done in the same way as the probability of air temperature ranges,
with the upper bounds for precipitation ranges set high enough that they are
effectively infinite.
> When working with this, I found that expressing percentiles and probabilities as dimensions, instead of attributes, made the relationship between them more intuitive.
I agree.
Cheers
Jonathan
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Received on Tue Dec 06 2011 - 07:42:36 GMT
