[CF-metadata] CF standard names for Ocean Dynamics

[Jonathan Gregory]

Dear Jenny

> I have sorted out the cell methods for daily mean and depth average velocities
Well done - that's not entirely trivial!

>  The "total" in total_eastward_sea_water_velocity was to indicate barotropic and baroclinic velocities, but it has been suggested that the standard name eastward_sea_water_velocity covers this.
That's right. In general I think "total" is to be avoided, because it is not
explicit. We should assume quantities include all relevant effects, components
etc. unless they explicitly indicate otherwise.

> We have had some discussions and have decided that using the standard name sea_floor_depth_below_mean_sea_level will be adequate though.  
Fine.

Best wishes

Jonathan