Find local pressure for fields on model levels

Pick any file that contains data you want to look at on model levels (any dm- or pm- file). Then use the following command:

    r.diag ggstat filename -info | less

You should see lines like the following:

    :
  pref=   100000.00000000000      Pa
    :
  Equation to compute hydrostatic pressure (pi): ln(pi) = A + B * ln(P0*100/pref)
  Momentum levels ip1, A, B:
   96649243   5.1943503239077842        0.0000000000000000
    :
  Thermodynamic levels ip1, A, B:
   96683587   5.3687530840411721        2.3925018330509525E-009
    :

You see the equation you need to solve above: ln(pi) = A + B * ln(P0*100/pref)
So in this example the local pressure is : pi = exp(A + B * ln(P0*100/pref))
The value for 'pref' is written above: pref = 100000
'P0' is the surface pressure for the current point and timestep.
If you are looking at winds you need to take ip1, A, B from the 'Momentum' level set, otherwise from the 'Thermodynamic' level set.
'ip1' is the model level "description". Once you read the field you want to plot you also have access to its 'ip1'. If you do not find them let me know. And once you have the ip1 you can get the corresponding 'A' and 'B' from the table above. I suggest you create a case of if statement, for example:

       if ip1 == 96649243:
          A = 5.1943503239077842
          B = 0.0000000000000000
and so on.