sediment settling flux

[Johnny.Zang]

Dear ROMS users,

I am working on the sediment-biological model coupling using COAWST and I found a problem regarding those sediment and biological tracers who have vertical settling velocity.

In sediment transport model (sed_settling.F), sediment tracer concentration is updated after settling flux calculation:
DO i=Istr,Iend
DO k=1,N(ng)
t(i,j,k,nnew,indx)=t(i,j,k,nnew,indx)+(FC(i,k)-FC(i,k-1))
END DO
settling_flux(i,j,ised)=FC(i,0)
END DO

While in biological model (here I use nemuro.h), PON and Opal (these two bio tracers have settling flux like sediment) concentration is updated using
DO k=1,N(ng)
DO i=Istr,Iend
Bio(i,k,ibio)=qc(i,k)+(FC(i,k)-FC(i,k-1))*Hz_inv(i,k)
END DO
END DO

An additional Hz_inv is included to transfer flux (mmol N/m2) to concentration (mmol N/m3). I am wondering why Hz_inv is not included in sediment model? I think these two models use the same method to estimate vertical settling flux, and settling flux should be divided by grid thickness (*Hz_inv(i,k)) to estimate its contribution to the tracer concentration variation at certain grid.

Does anyone have ideas on that?

Best,

John

[jcwarner]

be careful in here.

a quick look i can see the bottom of the bio routine has:
... DO i=Istr,Iend
cff=Bio(i,k,ibio)-Bio_old(i,k,ibio)
t(i,j,k,nnew,ibio)=t(i,j,k,nnew,ibio)+cff*Hz(i,j,k)
so to put the Bio back into the tracer array, the Bio gets multiplied by Hz. so that is probably where the units get back to what is needed.

[Johnny.Zang]

Dr. Warner,

Thank you for your reply. Now my understanding is t(i,j,k,nnew,ibio) is bio tracer concentration times Hz rather than bio tracer's concentration, and the units of t(i,j,k,nnew,ibio) and t(i,j,k,nstp,ibio) are different (mmol/m2 vs mmol/m3). Am I correct?

Best,

John

[jcwarner]

the tracer nnew time level is the "tracer * Hz". the tracer nstp time level is just the tracer value.
so yes, be careful.