[CF-metadata] New standard name requests for TSI and SSI

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 14 May 2015 17:30:14 +0100

Dear Peter and Judith

We are all specialists in our own fields. I didn't mean to imply that your
field is any more or less esoteric! I was just making the point that standard
name are often not the terms customarily employed. They aim to be more self-
explanatory for a wide range of disciplines. A standard name is often more
an answer to the question "What does that mean?" rather than "What do you
(usually) call that?" Working out names that are correct for the experts
concerned and comprehensible for others is often quite difficult, takes time
and is not infrequently frustrating (as this apparently is to you already).
However I think that it's because we (the CF community) have spent so many
hundreds or thousands of hours doing it that we have produced a vocabulary
people find useful. I hope that's true, anyway. If not, it's been a waste of a
non-negligible part of my working time at least for the last 15 years. :-)

I agree that when we don't use standard terms, it may be a problem for
someone who is looking up standard names in the table, with the aim of finding
the one they want. We can often help with this by mentioning other things
the quantity is called in its definition, so the user of the table will find
it easily by searching the definitions.

I agree that "flux" is not the exactly correct word. We did discuss this, 15
years ago, and for the record I would have preferred flux_density. But that
wasn't the choice we made, and now we have more than 200 standard names with
the word "flux" in them, meaning something per m2 (not necessarily radiation
- many of them are mass flux densities). We must be consistent, so the only
alternative is to rename them all. We could do that. That's a "detachable"
question which I'll post in another thread. I don't think it's black-and-white
because "flux" *is* very often used to mean m-2 quantities in geoscience. As
with language in general, usage determines correctness. There's no point in
saying something which is always used in a language is wrong. Languages are
just conventions, not physical laws.

An irradiance is a radiative flux density, isn't it. If that's correct, I think
it's clearer not to use the word "irradiance", because more people will under-
stand radiative flux density. Is there any extra meaning in "irradiance"?

There is a solution to the "shortwave" problem. We could call this quantity
solar_radiative_flux[_density], where "solar" just means "from the sun", of
course. We have many other standard names with "radiative_flux" in them, not
specifying wavelength range. The issue of "shortwave" came up because of
wanting to establish whether the quantity was one we already have a name for.

> "I'm not sure whether by TOA irradiance you mean the flux incident
> normal to the Earth's surface or parallel to the vector between Sun
> and Earth."
>
> I confess to not understanding it until you just added this:
> "These differ by a factor of 4." That was the clue I needed to
> understand your question although you've erred by a factor of two.

I don't think I have. toa_incoming_shortwave_flux is 1/4 of the quantity you
mean, when averaged over time, don't you agree.

Apart from the factor of 4, the additional point of your quantity is that it
is at_standard_orbital_radius, if I understand correctly.

So, if we had a standard name of
  solar_radiative_flux[_density]_at_standard_orbital_radius
would it be correct and comprehensible to an expert? Maybe they would ask
"Why didn't they call it TSI?" but that's not the question. Is it a correct
description of TSI? It would be useful to have a standard name for this
obviously important quantity.

Best wishes

Jonathan
Received on Thu May 14 2015 - 10:30:14 BST