Xylar Asay-Davis

@alicebarthel, I think since @mark-petersen won't be back until next Tuesday that you should go ahead and make a PR. We can do further testing as part of the review....

@alicebarthel, I will try to run some tests today or tomorrow. Thanks for submitting this!

# Testing I made a test merge of this branch with `master` (currently just one merge behind) and tested the result against `master` in both E3SM and compass on Anvil....

@alicebarthel, thanks for putting this in. @jonbob, do you think my testing is sufficient or should we wait for @mark-petersen to return and do a review?

Sounds great!

Thanks @jonbob. Sorry our other testing didn't turn this up. @cbegeman, do you have recommendations on how to handle this based on similar loops over edges elsewhere in the code?

It seems most likely that we need a check for valid `edgesOnVertex`. Presumably, we're using the dummy index for nonexistent edges on vertices and this is leading to `minLevelEdgeBot ==...

It seems like this code block shows how to do this properly: https://github.com/E3SM-Project/E3SM/blob/973a8f7147f75e7a0b8e6abd6ac4ee04b5a38f90/components/mpas-ocean/src/shared/mpas_ocn_vel_hmix_del4.F#L204-L217 We need to use `minLevelVertexBot` and `maxLevelVertexTop` rather than `minLevelEdgeBot` and `maxLevelEdgeBot`. @alicebarthel, would you like to...

@alicebarthel, that's great! I'll check with @jonbob in a bit but I think that will do for now.

@alicebarthel, the fix that @jonbob suggested might only work under RK4 if `normalVelocity` is defined for both valid and invalid edges (i.e. it is zero for edges between ocean and...