Using Sander's CH4 fields

For CO simulations, I am switching to Sander's latest CH4 fields. Along the way, I'm also modifying the way they are read. The first time they are read, they are coarsened according to the running region definition. During subsequent runs, the coarsened fields are read in. I will convert all of Sander's output fields to the new format, since that is likely the format that will be there going forward.

With the old CH4 field (coded by Pim), the budget over one month (forget the initial value, that's just arbitrary, starting from global 65 ppb) is

 --------------------------------------------------------
Budget of tracers in region glb600x400 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          3.22312E+11
     emitted   :          1.41387E+11
   chemistry   :         -1.43613E+11
    update_p   :          1.29686E+10
   advection   :         -5.02319E-02
  deposition   :         -6.89012E+09
stratosphere   :          0.00000E+00
  Final mass   :          3.26165E+11
Budget error   :         -9.42383E-02
 --------------------------------------------------------
 --------------------------------------------------------
Budget of tracers in region sea300x200 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          3.09878E+10
     emitted   :          7.44775E+09
   chemistry   :         -5.19502E+09
    update_p   :          1.11884E+10
   advection   :         -6.62135E+09
  deposition   :         -4.72521E+08
stratosphere   :          0.00000E+00
  Final mass   :          3.73350E+10
Budget error   :         -4.21448E-02
 --------------------------------------------------------
 --------------------------------------------------------
Budget of tracers in region sea100x100 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          1.56116E+10
     emitted   :          2.19059E+10
   chemistry   :         -8.39908E+09
    update_p   :          0.00000E+00
   advection   :         -6.63566E+09
  deposition   :         -2.31840E+09
stratosphere   :          0.00000E+00
  Final mass   :          2.01643E+10
Budget error   :          1.47724E-01
 --------------------------------------------------------

With the new CH4 field, coarsening on-line, the budget is

 --------------------------------------------------------
Budget of tracers in region glb600x400 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          3.22312E+11
     emitted   :          1.41525E+11
   chemistry   :         -1.43629E+11
    update_p   :          1.29707E+10
   advection   :          2.04956E-01
  deposition   :         -6.89137E+09
stratosphere   :          0.00000E+00
  Final mass   :          3.26287E+11
Budget error   :          2.02454E-01
 --------------------------------------------------------
 --------------------------------------------------------
Budget of tracers in region sea300x200 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          3.09878E+10
     emitted   :          7.45044E+09
   chemistry   :         -5.19639E+09
    update_p   :          1.11892E+10
   advection   :         -6.60557E+09
  deposition   :         -4.72536E+08
stratosphere   :          0.00000E+00
  Final mass   :          3.73529E+10
Budget error   :          1.72729E-02
 --------------------------------------------------------
 --------------------------------------------------------
Budget of tracers in region sea100x100 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          1.56116E+10
     emitted   :          2.19076E+10
   chemistry   :         -8.40009E+09
    update_p   :          0.00000E+00
   advection   :         -6.62674E+09
  deposition   :         -2.31837E+09
stratosphere   :          0.00000E+00
  Final mass   :          2.01740E+10
Budget error   :          1.59882E-01
 --------------------------------------------------------

And with the new CH4, reading pre-coarsened fields, the budget is

 --------------------------------------------------------
Budget of tracers in region glb600x400 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          3.22312E+11
     emitted   :          1.41525E+11
   chemistry   :         -1.43629E+11
    update_p   :          1.29707E+10
   advection   :          2.04956E-01
  deposition   :         -6.89137E+09
stratosphere   :          0.00000E+00
  Final mass   :          3.26287E+11
Budget error   :          2.02454E-01
 --------------------------------------------------------
 --------------------------------------------------------
Budget of tracers in region sea300x200 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          3.09878E+10
     emitted   :          7.45044E+09
   chemistry   :         -5.19639E+09
    update_p   :          1.11892E+10
   advection   :         -6.60557E+09
  deposition   :         -4.72536E+08
stratosphere   :          0.00000E+00
  Final mass   :          3.73529E+10
Budget error   :          1.72729E-02
 --------------------------------------------------------
 --------------------------------------------------------
Budget of tracers in region sea100x100 (Kg)
      Tracer   :             CO      
 --------------------------------------------------------
Initial mass   :          1.56116E+10
     emitted   :          2.19076E+10
   chemistry   :         -8.40009E+09
    update_p   :          0.00000E+00
   advection   :         -6.62674E+09
  deposition   :         -2.31837E+09
stratosphere   :          0.00000E+00
  Final mass   :          2.01740E+10
Budget error   :          1.59882E-01
 --------------------------------------------------------