Prerequisites and Run Notes

• Install MAG - The following tutorials assume you have already installed MAG following the instructions in Chapter 2 in the MAG User Manual.
• Delete, Move, or Rename Output Files - After each run, you must delete, move, or rename all of the output files in the current directory before re-running with the same "output" filename. Retaining same-named output files in the current directory causes MAG to crash.
• Changing Parameters - Physical and time-step parameters can be changed in the par-file namelist without re-compiling MAG. See Appendix B in the MAG User Manual for a list of the input parameter names and definitions. Grid parameters must be changed in param.f and MAG must be then re-compiled. There are some numerical restrictions on the grid parameter combinations, which are given in Appendix A.

Tutorial 1: Running Benchmarks

1. Uncompress all files, and create a path (see Chapter 2 of MAG User Manual)
2. Link the grid parameter file to param.f, which enters into most subroutines through "include" statements. For example, a grid parameter file named param32f4.f (32 is the spherical harmonics truncation degree; 4 is the longitude symmetry) is linked using:

       $ ln -sf param32s4.f param.f 
   

3. Compile the program as follows (renaming the executable in line 2 is optional):

       $ make
       $ mv magx magx32s4  
   

4. MAG uses a standard input file. Background execute using par.XXX as the input file and .YYY as the output file's extension, e.g., $ magx32s4 <par.XXX >p.YYY &, so to run with the benchmark input files (par.bnch0 or par.bnch1), the execution statement should be:

       $ magx32s4 <par.bnch0 >p.bench0 &
   

5. If there is a problem with the input file list, it is often the final three lines; with some systems, a "$" may be required at the end.
6. MAG produces a series of output files. For example, when using input file par.bnch0 (the example in step 4) MAG generates: l.bench0, ls.bench0, g[i].bench0 and d[i].bench0, where i=0,1,2...9. See Appendix B in the MAG User Manual for details on MAG's output files. Compare your output files with the data provided in the directory ~/bench-data/data_bench0.

Tutorial 2: Reversal Dynamo Case

In this example, we produce a magnetic field reversal using MAG. The input parameter in the source directory for this case is ~/src/par.Rev. There is no longitudinal symmetry in this case, so when you compile MAG, use param32s1.f linking to param.f. The Ekman number is E=0.02, the Prandtl number is Pr=1 and the magnetic Prandtl number is Pm=10. The Rayleigh number is Ra=12000.

1. Link param32s1.f to param.f:

       $ ln -sf param32s1.f  param.f 
   

2. Compile the program with:

       $ make
       $ mv magx magx32s4 
   

3. Background execute using par.Rev as the input file and p.rev as the output file (Note: The output file's extension is specified in the par-file, e.g., here par.Rev specifies that the outfile should be named filename.rev):

       $ magx32s4 <par.Rev >p.rev &
   

4. MAG will then execute and produce datafiles in the same directory. See Appendix B in the MAG User Manual for details on MAG's output files.

Results and Discussion

This case has run on 32-bit and 64-bit Intel processors. Figure 1 below shows a plot of mean velocity Vrms, mean magnetic field Brms, the axial dipole and the dipole tilt on the outer boundary. It indicated a magnetic field reversal between time steps 25 and 30.

Figure 2 shows a longer run of MAG, where we see the magnetic field reversed again. At this time, the magnetic field had weakened substantially.

In Figures 3 and 4 (below), the top figure is the pole plot before the second field reversal and the bottom is the pole plot after the second field reversal.

An additional tutorial on creating a Reversal Dynamo movie is found in Chapter 5 of the MAG User Manual