[CF-metadata] omega

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 9 Feb 2004 22:58:35 +0000

Dear All

Last year we replaced "omega" with the more explicit
vertical_air_velocity_expressed_as_tendency_of_pressure
but this is rather clumsy.

It has been suggested we should instead have
vertical_velocity_in_pressure_coordinates
Speaking for myself, I feel that this is not so good, although more familiar,
because I think the sign convention is not obvious, and I am worried it might
be mistaken for vertical velocity on pressure levels.

Mike Blackburn has pointed out that omega isn't strictly vertical velocity,
since pressure surfaces are not necessarily horizontal. Omega is actually the
rate of change of pressure of an air parcel. This suggests a new possibility:
langrangian_tendency_of_air_pressure
for omega. What do you think? I like this because it is accurate and shorter
than the others. We could define lagrangian_tendency in the guidelines. The
usual tendency is Eulerian. Plain tendency_of_air_pressure, which is already
a standard name, means the partial derivative wrt time e.g. of air pressure
measured at a synoptic station, whereas lagrangian_tendency means the total
derivative i.e. following a parcel.

The same argument would apply to vertical air velocity in sigma coordinates.

Cheers

Jonathan
Received on Mon Feb 09 2004 - 15:58:35 GMT