am 8/12/08
  code to calculate magnetic perturbation at the ground
  can be used for time- and tie-gcm
  The compiler flag in the Makefile has to be changed
  adjusting to either model.
  Basically there is no change between the two models, 
  but the number of levels is used
  at one place. That's the only reason.
  
  For how to run the model look into the doc directory.
  This document is older but it should still apply with minor
  differences.
  
  An example file is in the directory.
  
am 4/13/2011
  update code to 64 bit machines
  corrected a few errors
  put ncl scripts for plotting
  more information in src_code/Readme