Lagrangian particles and tracer fields interaction equations

[emmabeniston]

Hi all,

I recently got a bit confused about how the interaction equations/tendencies are applied to Lagrangian particles vs the coupled tracer fields (see documentation on individuals). This had led me to think I was having problems with mass conservation.

In the end I realised that the Lagrangian particles use the tendency as it is written by the user, but the tracer field divides the tendency by the cell volume.

OceanBioME.jl/src/Particles/tracer_interpolation.jl

Line 70 in 86bbfbc

atomic_add!(tendency, i, j, k, particle_tendency / node_volume)

In hindsight, this makes sense, because Lagrangian particles should deal with quantities in mass units, but tracer fields in concentration units.

I just thought I’d open a discussion about this in case this is something which could be confusing to other users. Perhaps it would be helpful to have a slightly more detailed example in the documentation, demonstrating how mass is conserved in the system?

Thanks!