[CF-metadata] statistic indices

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 20 Sep 2007 14:32:33 +0100

Dear Heinke

> > 90th percentile of air temperature = percentile_function (air_temperature
> > values, cumulative_probability = 90%)
> >
> You are right. But I am careful with the word 'probability', because
> for transient climate model runs
> we have different probability spaces and it must be clear what we count.

You mean the threshold is a percentile of a climatology, and then you use the
threshold to evaluate the probability of exceedance in a different climate.

> What do you think ?

I think it's quite difficult to describe this systematically and economically.

> > Since we are not using "frost days" elsewhere, I would suggest
> > number_of_days_with_air_temperature_below_threshold_and_zero_surface_snow_amount
> >
> > I think it is still worth considering the alternative approach for these
> > quantities with one or two thresholds of simple standard names such as
> > number_of_days and fraction_of_days, and rely on the coordinate variables
> > alone to indicate the conditions that apply.

What I meant was, perhaps we could have a standard name of number_of_days and
allow it to be inferred what the conditions are from the presence of
coordinate variable specifying thresholds. For instance, if there were a
coordinate variable with a standard name of lower_bound_of_air_temperature
(say) it could be deduced that we mean the number of days when the air
temperature exceeds this lower bound. This would move more of the definition
of the quantity into the coordinate variables.

I am concerned that these derived quantities are hard to name. I wonder if we
are doing this the wrong way. Let me ask a hypothetical question: how would
you identify these various indices etc. in netCDF without trying to use CF
standard names? Let us consider only those quantities which you actually have
a present need for, as I am sure we can imagine indefinitely complicated cases
without trying hard!

Best wishes

Jonathan
Received on Thu Sep 20 2007 - 07:32:33 BST