Dear Bert,
Many thanks for your comments and suggestions.
In the proposed new standard names, the word "sedimentation"
was meant to represent the gravitational settling of cloud
liquid water droplets.
I agree that the above usage of "sedimentation" does not
match a transition from one medium to another. Therefore,
we may need to look for another word to avoid confusion.
As an alternative, the suggested word "settling" sounds
good to me. In this case, the proposed standard names
will be as follows;
(a) tendency_of_mass_fraction_of_stratiform_cloud_liquid_water
_in_air_due_to_settling_of_cloud_liquid_water,
and
(b) tendency_of_mass_fraction_of_stratiform_cloud_condensed_water
_in_air_due_to_settling_of_cloud_liquid_water.
Best wishes,
Tomoo
----- Original Message -----
From: "Bert Jagers" <[email protected]>
To: "Tomoo Ogura" <[email protected]>; "Cameron-smith, Philip" <[email protected]>; "Jonathan
Gregory" <[email protected]>
Cc: "Jennifer Kay" <[email protected]>; "Yoko Tsushima" <[email protected]>;
<[email protected]>
Sent: Wednesday, March 09, 2011 9:22 AM
Subject: Re: [CF-metadata] Proposal for new standard names - use of
"sedimentation"
Dear all,
Unfortunately I have had far too little time to contribute to the CF mailing list over the past
year, but I try to scan the titles of mails coming in and now and then I read a post. I didn't
intend to read this thread until my eye accidentally caught the word "sedimentation" in body text.
As someone involved in sediment transport in rivers, estuaries, coastal areas and to a much lesser
oceans, I do have a strong association with the word "sedimentation". As a result I have some
concerns with the appropriateness of the chosen word.
If I interpret the most recent discussion correctly, the proposal is to use the word
"sedimentation" for the slow downward motion of liquid water in the atmosphere; not being an
atmospheric scientist I'm trying to grasp what that actually means. The discussion distinguishes
it from definitions including terms like "accretion" and "autoconversion" which based on the
description in the standard name table both seem to be related the growth of droplets and ice
crystals; flocculation is the associated process in cohesive sediment modeling. Other processes
that thus would be included in your new definition of "sedimentation" include: vertical advection
due to general air velocity, turbulent mixing, relative gravitational settling of the
droplets/crystals, ... more?
In sediment transport, the words "sedimentation" and "deposition" are generally used to mean the
reverse of "erosion". The former two mean that sediment falls from suspension onto the bed ("ocean
floor"), whereas "erosion" means the uptake of sediment from the bed by the flow. Now, let us see
how the word "sedimentation" was used before in CF names. The term "sedimentation" has so far been
used in three standard names related to the ocean_mole_content of three chemical substances. These
names are associated with 2D quantities (quantities per unit area) which matches my interpretation
of the word (and the common use of this word): the amount of the substances considered (carbon,
elemental nitrogen, and iron) in the ocean column is reduced due to the fact that organic
suspended sediment settles onto the ocean floor. Basically it includes a transition from one
medium (in the water column) to another medium (in/on the ocean floor). The newly proposed use of
the term "sedimentation" does not match such a transition.
Thinking along these lines I looked at the word "deposition" which is used more frequently in
standard names. However, mostly it is used in combination with "dry", "wet" or "turbulent" and
seem to be associated with the transition of substances from medium atmosphere to the medium ocean
(or land): a 2D flux field of 2D variable "atmosphere mass content" in line with the use of the
word "sedimentation" described above. The word "deposition" without "dry" or "wet" is less
uniquely tied to a specific process. It has been used as the reverse of "sublimation" in
tendency_of_mass_fraction_of_stratiform_cloud_ice_in_air_due_to_deposition_and_sublimation, as the
sum of "dry deposition" and "wet deposition" (= "turbulent deposition" + "gravitational
settling"), and in a non-specified manner in
tendency_of_ocean_mole_content_of_iron_due_to_deposition_and_runoff_and_sediment_dissolution.
In ocean modeling I would tend to use the word "settling" for the downward motion of sediment
relative to the water without necessarily hitting the ocean floor, but also the word "settling"
has so far only been used in combination with 2D variables of type "atmosphere mass content" and
deposition.
Best regards,
Bert
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