Confusion about DAMEE4 test

[mengqingjun]

I am testing the DAMEE_4 application in the test directory.There is no *_bry.nc inputing, and the Lateral Boundary Condition Type are all "CLO". It is obvious that ROMS get the boundary condiations from the damee4_Lclm_b.nc. If so, I check the damee_4.h, I find that #define TCLIMATOLOGY and #define TCLM_NUDGING. It shows that the model is forced via a nudging to the tracer climatologies. I also check the reference <Model evaluation experiments in the North Atlantic Basin: simulations in nonlinear terrain-following coordinates>,it said that "Buffer zones are applied at the northern and southern boundaries (3 degrees wide in either case) and in the Gulf of Cadiz to emulate interbasin exchange processes. In these nudging zones, temperature and salinity are relaxed to observed monthly T and S(climatology)with relaxation times of 5 days at the domain boundaries increasing to 60 days at the interior edge of the buffer zone." I check the ana_nudgcoef.h that

Code: Select all

!  Set tracer nudging coefficients in the southern and northern edges
!  from a five days time scale at the boundary point to decrease
!  linearly to 60 days seven grids points away from the boundary.
!
      cff1=1.0_r8/(5.0_r8*86400.0_r8)
      cff2=1.0_r8/(60.0_r8*86400.0_r8)
      DO j=JstrR,MIN(8,JendR)
        DO i=IstrR,IendR
          wrk(i,j)=cff2+REAL(8-j,r8)*(cff1-cff2)/7.0_r8
        END DO
      END DO
      DO j=MAX(JstrR,Mm(ng)-7),JendR
        DO i=IstrR,IendR
          wrk(i,j)=cff1+REAL(Mm(ng)-j,r8)*(cff2-cff1)/7.0_r8
        END DO
      END DO

There are seven grids poins away from the boundary and resolution is 3/4 degrees.So the buffer zones areas is (3/4)*7 = 5 degrees.It seems not agree with the "Buffer zones are applied at the northern and southern boundaries (3 degrees wide in either case".
Actually , I don't know how the buffer zone are applied and what "5 days" and "60 days" is really meaning. How the so called nudging zones northern and southern "open" boundaries are open while the the Lateral Boundary Condition Type are all "CLO"?

Anyone could help me ?
I am looking forward your replies!
Thanks!

[kate]

Oh yeah, DAMEE. That was a model intercomparison project long, long ago with externally applied specifications so that all models were supposedly doing the same thing. Those choices are not how we currently run anything and in fact Hernan got best results by not following the original guidelines. There are now global ocean models which we can use for RadNud boundary conditions and any of them should lead to better behavior than using monthly T,S climatologies from observations.

[mengqingjun]

Thank you for your replies Kate !Because I am a newer to ROMS, so I want get familiar with it through runing as mang test cases as possible.

There are now global ocean models which we can use for RadNud boundary conditions and any of them should lead to better behavior

Could I think that the *_clm.nc will not be used and only the *_bry.nc is OK ?
ps. I am wondering how to prepare ROMS *_bry.nc input file using d_obc_roms2roms.m or d_obc_mercator.m? What is Mercator dataset or ROMS NWA dataset that being used ?How I can get the Mercator dataset or ROMS NWA dataset for my own application ?
Thanks !

[kate]

Could I think that the *_clm.nc will not be used and only the *_bry.nc is OK ?

Yes, it should be OK. Try that first and if it isn't good enough, then you can add back in the climatology nudging in a band near the boundary.

[mengqingjun]

Thank you Kate and I will have a try !

[mengqingjun]

It seems that the longer Nudging time scale (days) the weaker the nudging.
But in ana_nudgcoef.h:
IF (DOMAIN(ng)%SouthWest_Test(tile)) THEN
Tobc_out(itrc,ng,iwest)=Tnudg(itrc,ng)
Tobc_in (itrc,ng,iwest)=obcfac(ng)*Tnudg(itrc,ng)
END IF
As recommended in ocean.in, OBCFAC > 1; at the same time, Tnudg is the value TNUDG suplied in thh ocean.in,the so called Nudging time scale (days), absolutely Tnudg > 1;
So, Tobc_in > Tobc_out,does that means nudging on inflow is stronger than on outflow ?

[kate]

The value in Tnudg is inverted after it is read in. This is the code in read_phypar.F:

Code: Select all

!
!  Compute inverse nudging coefficients (1/s) used in various tasks.
!
          IF (Tnudg(itrc,ng).gt.0.0_r8) THEN 
            Tnudg(itrc,ng)=1.0_r8/(Tnudg(itrc,ng)*86400.0_r8)
          ELSE 
            Tnudg(itrc,ng)=0.0_r8
          END IF

[mengqingjun]

Oh,you mean that the Tnudg value in ocean.in is first read by the file read_phypar.F and the Tnudg value is used the inversed value !
I see, thank you Kate!
ps. Except for TCLIMATOLOGY TCLM_NUDGING that will compile ana_nudgcoef.h,what other else CPP definitations that will compile ana_nudgcoef.h ?
QCORRECTION SRELAXATION for example,does they compile ana_nudgcoef.h? Any other ones else ?Could you give me some examples ? Because I what have a try if I don't compile ana_nudgcoef.h ,what the results will be like.
Thank you !

[kate]

Use the source, Luke.

Your ultimate answer to questions like this are to see what ROMS is doing. Check globaldefs.h to see which options turn on which other options. Look at $SCRATCH_DIR/analytical.f90 to see what the result of all that C preprocessing is. grep for strings like Tnudg to see how they are used.