[CF-metadata] omega

[Brian Eaton]

Hi Jonathan and Bryan,

I agree with Jonathan that "lagrangian_tendency_of_air_pressure" seems like
a good description for the total, substantive, or material (take your pick)
derivative Dp/Dt.

Bryan wrote:
> are partly Lagrangian, but when we calculate them in a model using
> differencing schemes that require us to evaluate the derivatives by using 
> Eulerian coordinates, they're Eulerian quantities.

I don't understand this statement.  There are relationships that allow one
to compute material derivatives (following a material parcel) from the
partial derivatives obtained from a fixed (Eulerian) coordinate system.
Are you suggesting that a material derivative is an Eulerian quantity?  I
think of it as a Lagrangian quantity.

I'm actually comfortable with either Jonathan's suggestion or with Bryan's
preference of "vertical_velocity_in_pressure_coordinates" as that is a
commonly used description of omega.  But I don't understand the argument
against using the term Lagrangian.  My preference (currently) is
lagrangian_tendency_of_air_pressure.

Brian


On Wed, Feb 11, 2004 at 05:38:09PM +0000, Jonathan Gregory wrote:
> Dear Bryan
> 
> I don't really understand, I'm afraid. Perhaps I'm using wrong terminology.
> What more accurate term for D/Dt could we use instead of Lagrangian tendency?
> If we can choose a term for it, then it seems a clear and simple distinction to
> me that can be made between omega=Dp/Dt on the one hand and partial dp/dt on
> the other, which we have already called tendency_of_air_pressure.
> 
> > (see also Dtheta/Dt expressed as and called an "isentropic 'vertical 
> > velocity'" where the inner quotes are David's, in AHL, Middle Atmosphere
> > Dynamics, p138).
> 
> I think the inner quotes imply that he's calling it a vertical velocity as a
> kind of useful analogy, not because Dtheta/Dt is really a velocity in the
> popularly understood sense of the term. It is instead "standing in" for a
> vertical velocity.
> 
> > I really think we are trying to put too much information in one box (the 
> > standard name).  I think standard bloat is a real issue to be careful of.
> > Don't we have a description field for the extended explanation?
> 
> All we are trying to do is choose a name for omega! If we can't agree on a
> reasonably short and unambiguous phrase for it, then I do think we should just
> call it omega instead and explain what it is in the extended description.
> 
> Best wishes
> 
> Jonathan
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