id,summary,reporter,owner,description,type,status,priority,milestone,component,version,severity,resolution,keywords,cc,branch_review,mp_status,wp_comment
1540,Tracer conservation (2): Surface vertical velocity with source terms in hdivn,jchanut,nemo,"I have trouble to understand the rationale in including a source term with a barotropic component in the model divergence (this occurs with rivers and ice shelves in particular). Considering the continuity equation and z* coordinate, integrating vertically, we actually have an unusual cancellation of the river runoff contribution at the surface (while one should expect -(E-P-R) ).
The net component of river fluxes has already been accounted for in the volume variation, and its projection onto cell volumes is implicitly chosen to be uniform (in domvvl). This could be different, but its seems natural that all the terms in the barotropic equation are treated the same way in modifying the model thicknesses under the z* paradigm.
I suggest that the projection of the barotropic component due to river fluxes should be removed in the divergence term, which allows to recover right vertical fluxes (with expected w surface value). One simply add it in the sea level equation instead of summing vertically the divergence.
The existing code does conserve volume globally, but, I think, not locally, if one consider what is done in trasbc. To be discussed.",Bug,closed,normal,,OCE,trunk,,invalid,,,,,