[MITgcm-support] DRhoDr Diagnostic

[Ryan Abernathey]

I am trying to understand *precisely* where the diagnostic DRHODR is  
calculated the vertical dimension. Here is the relevant line from  
available_diagnostics.log:

   69 |DRHODR  | 42 |SM      LR      |kg/m^4          | 
Stratification: d.Sigma/dr (kg/m3/r_unit)

According to the documentation (http://mitgcm.org/r2_manual/latest/ 
online_documents/node262.html), SM means "scalar mass point," which  
would imply it is on the "C-grid," with RC giving the vertical  
position. (I don't understand what LR means.) However, several people  
have told me that DRHODR is actually at the cell interface, with RF  
giving the vertical position.

The stratification is actually calculated in grad_sigma.F in the  
following lines:
          sigmaR(i,j,k)= maskC(i,j,k,bi,bj)
      &                *recip_drC(k)*rkSign
      &                *(sigKp1(i,j)-sigKm1(i,j))

This seems to imply that the true vertical position of sigmaR is  
exactly half-way between C points. This only corresponds with the F  
point when the cells are evenly spaced.

Can someone help clear up my confusion?

Thanks!
__________________
Ryan Abernathey
rpa at mit.edu
MIT Ph.D. Student
Program in Oceans Atmospheres & Climate
http://web.mit.edu/rpa/



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