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6th Order Horizontal Diffusion (diff_6th_opt) recommendation

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New member
I would like to ask about the 6th Order Horizontal Diffusion (diff_6th_opt).
The default option, the option that comes in the namelist.input, is diff_6th_opt=0. However, the ARW User’s Guide Version 4 informs that "Option 2 is recommended".
I would like to ask why option 2 is recommended? or should I use none (diff_6th_opt=0)?

What the wording in the Users' Guide should actually say is that this option is set to 0, by default, as it's not necessary for most users; however, if you are going to use it, you should use option 2. I will modify the Users' Guide so that this is more clear. If you're interested in reading more about diff_6th_opt and why it may be sometimes used, you can read the publication about it here.