divergence is not right? about windspharm HOT 4 CLOSED

I think you should consider applying spectral truncation before computing the divergence, the gradients are small compared to the fields and the result is a noisy divergence field (i.e. use the truncation= keyword argument when calling divergence).

I would not expect the gradient operators to reproduce the result of divergence, and even in your first example they do not match very well away from the equator. A truncated input to divergence will do a better job.

I also noticed the units of your field are unusual, values are of the order 1e11. This should not actually cause a problem though.

from windspharm.

Thanks, @ajdawson !

After applying a truncation to the calculation, the divergence field becomes much better.

But I have a further question, different truncation returns different results. Then what is the optimal truncation I can use?

from windspharm.

I don't think there is an optimal truncation as such. Truncation is just filtering out smaller scale variations in the original field (smoothing them) before computing divergence. Choice of truncation depends somewhat on what scale features you are interested in.

from windspharm.

Thanks! I now feel more confident to use the truncation.

Close the issue.

from windspharm.