[MITgcm-support] Advice on RBCS

[Christopher L. Wolfe]

Hi modelers,

I'm trying to do some Lagrangian diagnostics to determine what  
fraction of the water at point (x,y,z) was last exposed to the  
surface in the certain geographical region. I'd like to do this by  
using a ptracer which is (rapidly) relaxed relaxed to 1 in a certain  
surface patch, 0 over the rest of the surface, and not relaxed in the  
interior. The initial condition for the ptracer is the same as the  
relaxation pattern. I think I've got the ptracers package configured  
correctly, but I don't think the rbcs package is working correctly,  
as the total amount of ptracer remains quite close to the initial  
value, while the surface concentration rapidly decays toward zero.  
I'm not entirely sure what I'm doing with the rbcs package, so any  
advice would be appreciated.

The configuration files follow.

Thanks for your help,
Christopher

My data.ptracers file is

&PTRACERS_PARM01
PTRACERS_numInUse=2,
% model is started from pickup. 0014850000.data
PTRACERS_Iter0=0014850000,
# tracer 1 -
PTRACERS_names(1)='tracer01',
PTRACERS_long_names(1)='tracer01',
PTRACERS_units(1)='mol/m3',
PTRACERS_advScheme(1)=33,
PTRACERS_diffKh(1)=8.e-5,
PTRACERS_diffKr(1)=8.E-5,
PTRACERS_useGMRedi(1)=.FALSE. ,
PTRACERS_useKPP(1)=.FALSE. ,
PTRACERS_initialFile(1)='tracer01_init.bin',
# tracer 2 -
PTRACERS_names(2)='tracer02',
PTRACERS_long_names(2)='tracer02',
PTRACERS_units(2)='mol/m3',
PTRACERS_advScheme(2)=33,
PTRACERS_diffKh(2)=8.e-5,
PTRACERS_diffKr(2)=8.E-5,
PTRACERS_useGMRedi(2)=.FALSE. ,
PTRACERS_useKPP(2)=.FALSE. ,
PTRACERS_initialFile(2)='tracer02_init.bin',
/

My data.rbcs is
&RBCS_PARM01
tauRelaxT = 0.,
tauRelaxS = 0.,
relaxMaskFile(1) = ' ',
relaxMaskFile(2) = ' ',
relaxMaskFile(3) = 'tracer01_mask.bin',
relaxMaskFile(4) = 'tracer02_mask.bin',
relaxTFile = ' ',
relaxSFile = ' ',
rbcsIniter = 0,
rbcsForcingPeriod = 15552000.,
rbcsForcingCycle = 0.,
useRBCtemp = .FALSE.,
useRBCsalt = .FALSE.,
useRBCptracers = .TRUE.,
/

&RBCS_PARM02
useRBCptrnum(1)=.TRUE.,
tauRelaxPTR(1) = 1200.,
relaxPtracerFile(1) = 'tracer01_init.bin',
useRBCptrnum(2)=.TRUE.,
tauRelaxPTR(2) = 1200.,
relaxPtracerFile(2) = 'tracer02_init.bin',
/

The init and mask files are generated by the following matlab script:

% Dimensions of grid
NX=448;
NY=1792;
NZ=20;

ieee='b';
accuracy='real*8';

ixS = 1:round(NY/8);
ixN = NY-round(NY/8):NY;

% the topography
mask = ones(NX,NY);
mask(:,NY) = 0;
mask(NX,round(NY/8)+1:NY) = 0;

tracer01_init = zeros(NX,NY,NZ);
tracer02_init = zeros(NX,NY,NZ);
tracer01_mask = zeros(NX,NY,NZ);
tracer02_mask = zeros(NX,NY,NZ);

tracer01_init(:,ixN,1) = 1;
tracer02_init(:,ixS,1) = 1;
tracer01_mask(:,:,1) = 1;
tracer02_mask(:,:,1) = 1;

% don't relax inside the walls
for nz = 1:NZ
    tracer01_init(:,:,nz) = mask.*tracer01_init(:,:,nz);
    tracer02_init(:,:,nz) = mask.*tracer02_init(:,:,nz);
    tracer01_mask(:,:,nz) = mask.*tracer01_mask(:,:,nz);
    tracer02_mask(:,:,nz) = mask.*tracer02_mask(:,:,nz);
end

fid = fopen('tracer01_init.bin','w',ieee);
fwrite(fid,tracer01_init,accuracy);
fclose(fid);

fid = fopen('tracer02_init.bin','w',ieee);
fwrite(fid,tracer02_init,accuracy);
fclose(fid);

fid = fopen('tracer01_mask.bin','w',ieee);
fwrite(fid,tracer01_mask,accuracy);
fclose(fid);

fid = fopen('tracer02_mask.bin','w',ieee);
fwrite(fid,tracer02_mask,accuracy);
fclose(fid);


-----------------------------------------------------------
Dr. Christopher L. Wolfe                   858-534-4560
Physical Oceanography Research Division    OAR 357
Scripps Institution of Oceanography, UCSD  clwolfe at ucsd.edu
-----------------------------------------------------------




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