[CF-metadata] [Standard name request] property changes over time

From: Paul.Durack at csiro.au <Paul.Durack>
Date: Thu, 28 Apr 2011 10:20:16 +1000

Fair enough Jonathon..

Ok, then to ensure consistency with current expressions can I then request the following variable names (I've added two more..):

change_over_time_in_sea_water_salinity
change_over_time_in_sea_water_temperature
change_over_time_in_sea_water_potential_temperature
change_over_time_in_sea_water_density
change_over_time_in_sea_water_potential_density
change_over_time_in_sea_water_neutral_density

Cheers,

P

-----Original Message-----
From: Jonathan Gregory [mailto:j.m.gregory at reading.ac.uk]
Sent: Thursday, April 14, 2011 6:06 PM
To: Durack, Paul (CMAR, Hobart)
Cc: CF-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] [Standard name request] property changes over time

Dear Paul

We don't see to be speaking the same language. As I understand it these four
quantities you are proposing should all be change_over_time_in_X. That's what
they are, isn't it?

> sea_water_salinity_change
> sea_water_temperature_change
> sea_water_potential_temperature_change
> sea_water_density_change

change_over_time_in_sea_water_salinity etc. would be consistent with these
names that you pointed out:

> change_over_time_in_atmosphere_water_content_due_to_advection
> change_over_time_in_surface_snow_amount

These quantities are not changes over time:

> change_in_atmosphere_energy_content_due_to_change_in_sigma_coordinate_wrt_surface_pressure
> change_in_energy_content_of_atmosphere_layer_due_to_change_in_sigma_coordinate_wrt_surface_pressure

These quantities have _change at the end because in their case, unusually,
the quantity doesn't make sense as an "absolute" value, but only as a change.
That is, there is no such quantity as "global average thermosteric sea level"
for instance. That's why these names are not change_over_time_in:

> global_average_sea_level_change
> global_average_steric_sea_level_change
> global_average_thermosteric_sea_level_change

These quantities (and many other others) are all time-derivatives, for which
we consistently use the phrase tendency_of:

> tendency_of_air_density
> tendency_of_air_pressure
> tendency_of_air_temperature

That is not the same as change_over_time_in because it's got different physical
dimensions (units). A tendency is a change_over_time divided by the length of
the time interval (for infinitesimal intervals, anyway). The CF standard names
have canonical units, defining their physical dimensions, and quantities
always have different standard names if their physical dimensions differ. Hence
we could not have the same standard name for change_over_time and tendency
quantities.

In summary, I think the variety of expressions we have used in existing
standard names is quite systematic and indicates meaningful distinctions.

Best wishes

Jonathan
Received on Wed Apr 27 2011 - 18:20:16 BST