function CalcOcnForcingFields(cplFiles,gridFiles,prevFocnFiles,period,...
                              outDir,FocnRoot,focnRoot,iitC,fitC,ditC,...
                              dtC,gWeight,FocnOnly,InspectFocn,Inspectfocn)

fields = {'icL','taux','tauy','EmP','Qnet'};
mncfld = {'SIC','TX'  ,'TY'  ,'FW' ,'HF'  };

gravity = 9.81;

warning off MATLAB:MKDIR:DirectoryExists;
mkdir(outDir);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                 Load Data                               %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

datacpl = rdmnc(cplFiles,'iter','HFtave','TXtave',...
                         'TYtave','FWtave','SICtave');
datagrd = rdmnc(gridFiles,'rA','XG','YG','XC','YC');
RAC = datagrd.rA;
XC = datagrd.XC; XG = datagrd.XG(1:size(RAC,1),1:size(RAC,2));
YC = datagrd.YC; YG = datagrd.YG(1:size(RAC,1),1:size(RAC,2));
%save('DataPerCpl.mat','datacpl','RAC','XG','YG','XC','YC');
%load('DataPerCpl.mat');


% If a new focn is to be calculated, the old Focn must be loaded.
if ~FocnOnly
    for ifield=1:length(mncfld)
        filename = [prevFocnFiles,'/',FocnRoot,'.',...
                   fields{ifield},'.bin.',num2str(period-1)];
        fid=fopen(filename,'r','b');
        dataFocnOld.(mncfld{ifield}) = ...
            reshape(fread(fid,'real*8'),size(RAC));
        fclose(fid);
    end
end


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                      Select Coupled Field Data                          %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

test  = ismember([iitC:ditC:fitC],datacpl.iter);
index = ismember(datacpl.iter,[iitC:ditC:fitC]);
if ~isempty(find(test==0))
    error('Specified indecies not present in cpl_tave.* files!!');
end
for ifield = 1:length(mncfld)
    dataCplSelect.([mncfld{ifield},'tave']) = ...
        datacpl.([mncfld{ifield},'tave'])(:,:,index);
end


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                            Prepare Focn                                 %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% What if it is not in year increments?  Need a more sophisticated
% treatment of finding Focn.  Should compute monthly mean before.  Test
% with various sorts of coupled field outputs.

for ifield = 1:length(mncfld)
    FocnOld = dataFocnOld.(mncfld{ifield});
    if isequal(mncfld{ifield},'FW')
        FocnOld = DataCorrections(FocnOld,mncfld{ifield},gravity,RAC);
    end
    FocnNew = mean(dataCplSelect.([mncfld{ifield},'tave']),3);
    FocnNew = DataCorrections(FocnNew,mncfld{ifield},gravity,RAC);
    if FocnOnly
        Focn = FocnNew;
    else
        Focn = (gWeight*FocnOld + FocnNew)/(gWeight+1);
    end
    fid=fopen([outDir,'/',FocnRoot,'.',fields{ifield},...
               '.bin.',num2str(period)],'w','b');
    fwrite(fid,Focn,'real*8');
    fclose(fid);
    dataFocn.(mncfld{ifield}) = Focn;
end


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                         Prepare focn as needed                          %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if ~FocnOnly
    
    years = [iitC:ditC:fitC].*dtC./31104000;
    yrfrc = rem(years,floor(years));
    yrfrc(yrfrc == 0) = 1;
    uyrfrc = sort(unique(yrfrc));
    length(yrfrc)
    length(uyrfrc)
    
    for ifield = 1:length(mncfld)
        
        % Make yearly forcing file.
        focnFull = dataCplSelect.([mncfld{ifield},'tave']);
        focn = NaN.*zeros([size(RAC,1),size(RAC,2),length(uyrfrc)]);
        for itime = 1:length(uyrfrc)
            index = find(uyrfrc(itime) == yrfrc);
            focn(:,:,itime) = mean(focnFull(:,:,index),3);
        end
        if ~isempty(find(isnan(focn(:))))
            error('NaNs in ocean forcing files!!');
        end
        
        % Remove mean, add Focn
        SubMean = mean(focn,3);
        AddMean = dataFocn.(mncfld{ifield});
        for itime = 1:size(focn,3)
            focn(:,:,itime) = focn(:,:,itime) - SubMean + AddMean;
        end
        
        % Where ice, make Tau_x, Tau_y equal zero.
        if isequal(mncfld{ifield},'SIC')
            iceMask = (focn==0);
        elseif ismember(mncfld{ifield},{'TX','TY'})
            focn = focn.*iceMask;
        end
        
        
        focnmean = mean(focn,3);
        focnmean = sum(focnmean(:).*RAC(:))./sum(RAC(:));
        disp([mncfld{ifield},' mean:  ',num2str(focnmean)]);
        
        fid=fopen([outDir,'/',focnRoot,'.',fields{ifield},'.bin'],'w','b');
        fwrite(fid,focn,'real*8');
        fclose(fid);
    end
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                            Inspect Focn                                 %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if InspectFocn
    for ifield = 1:length(mncfld)
        fid=fopen([outDir,'/',FocnRoot,'.',fields{ifield},...
                   '.bin.',num2str(period)],'r','b');
        Focn = reshape(fread(fid,'real*8'),size(RAC));
        fclose(fid);
        figure(ifield);
        merccube(XG,YG,Focn); colorbar;
        title(mncfld{ifield});
    end
end

if Inspectfocn
    for ifield = 1:length(mncfld)
        figure(ifield); orient tall;
        fid=fopen([outDir,'/',focnRoot,'.',fields{ifield},'.bin'],'r','b');
        focn = reshape(fread(fid,'real*8'),[size(RAC),12]);
        fclose(fid);
        crange = [min(focn(:)),max(focn(:))];
        for ii = 1:size(focn,3)
            subplot(4,3,ii); merccube(XG,YG,focn(:,:,ii));
            shading flat; caxis(crange); colorbar;
            title([mncfld{ifield},' month ',num2str(ii)]);
        end
    end
end


% Field dependent data corrections.
function CorrectedData = ...
  DataCorrections(DataToCorrect,CorrectionField,gravity,RAC)
    if     isequal(CorrectionField,'SIC')
        CorrectedData = gravity.*DataToCorrect;
    elseif isequal(CorrectionField,'FW')
        offset = sum(DataToCorrect(:).*RAC(:))./sum(RAC(:));
        CorrectedData = DataToCorrect - offset;
    else
        CorrectedData = DataToCorrect;
    end