[MITgcm-support] How to output b (buoyancy) using MITgcm?

[Brainf]

Hi mitgcm,
    I want to simulate internal waves using MITgcm. I am very interested in what 
Sonya Legg have done like "Internal wave breaking at concave and convex continental" research.
    I found he plotted b(buoyancy) contour to see internal waves, and said the contour interval is △b=9.81*10^(-6)m/s^2 ,but how to output this?  The traditional output  files are  U V W T S and ETA; buoyancy is not included. I checked available diagnostics, can't find variable buoyancy also. Do I need to edit the mdsio package output source code? 
    I start from  verification/internal_wave experiment,and have change the resolution to 640x100.


Best regards. 

Brainf
brainf at 163.com
2006-12-04