[CF-metadata] rainfall

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 3 Jun 2004 13:02:58 +0100

Dear Sue

> Could you clarify something for me please. If I have a variable called
> 'rainfall in period' with units of mm, would the CF standard term now be
> lwe_thickness_of_rainfall_amount with canonical units of 'm'?

Since rainfall is already liquid, we don't need to say it's a liquid water
equivalent. Thus, we have rainfall_rate (m s-1) but lwe_snowfall_rate (m s-1).

We need to add names for the actual "depth" of precipitation, whether rainfall
(which is what you want) or snowfall. What should we call this? The word
"amount" might often be chosen, but we have already used that for kg m-2.
Unfortunately common phraseology might call quantities in mm or in kg m-2
both "rainfall amount" but we need different standard names since they have
different units (although numerically equal in this case).

I used the word "depth" above but a problem with rainfall/snowfall_depth would
be that "depth" usually means a vertical coordinate, not the vertical extent
of a layer, which is "thickness". This is just for self-consistency, of course,
which isn't the only criterion. We could call them
thickness_of_rainfall/snowfall_amount or rainfall/snowfall_thickness - what do
you (or others) think of any of these? Can you suggest better possibilities?

While we're on the subject, I wonder whether "thickness_of" is really needed
in the lwe names. The point of "liquid water equivalent" is that the quantity
is being expressed in volumetric terms assuming the density of liquid water.
Is it therefore obvious that we mean the thickness of a layer in
lwe_thickness_of_atmosphere_water_vapor_content
lwe_thickness_of_snowfall_amount
for instance? Could we rename these simply as
lwe_atmosphere_water_vapor_content
lwe_snowfall_amount?
There are nine of these (search on lwe_thickness to see them using the new
standard name search facility).

Best wishes

Jonathan
Received on Thu Jun 03 2004 - 06:02:58 BST