Adjust the along_isobath_averaging recipe to account for the vertical grid in ACCESS-OM2

[taimoorsohail]

The ht and hu variables for bathymetry use the actual vertical water column height in ACCESS-OM2-01, while variables like temp have fixed st_ocean_edges. To average along isobaths, I currently define a new bathymetric field, called ht_coarse or hu_coarse, that uses the NaNs in variables like temp and u to bin in isobaths.

We need to think about how/whether to incorporate the actual bathymetry in the binning here, and consider whether the current workaround is reasonable.

[adele-morrison]

I think we should use the correct cell thickness (i.e. not use st_ocean_edges for binning), because otherwise locations could get put in the wrong isobath bins, with an error of up to 180m or so for deeper/thicker cells.

[navidcy]

Could we elaborate a bit? The "correct" thickness cells variable name is what the st_ocean vertical grid?

@taimoorsohail what do you mean by "I currently define"? Are you referring to how the averaging is done in the along-isobath averaging recipe at the moment?

[taimoorsohail]

@taimoorsohail what do you mean by "I currently define"? Are you referring to how the averaging is done in the along-isobath averaging recipe at the moment?

Yes that is correct. That is what is currently done in the recipe.

I think we should use the correct cell thickness (i.e. not use st_ocean_edges for binning), because otherwise locations could get put in the wrong isobath bins, with and error of up to 180m or so for deeper/thicker cells.

What about variables like temp that are aligned to specific st_edges_ocean grid boundaries? Do you linearly interpolate onto the correct cell thickness?

[adele-morrison]

Variables like temp have a thickness defined by dzt, which at the bottom is aligned with ht, not st_edges_ocean. They're just output on the st_ocean grid for ease of saving.

[navidcy]

What is ht if it's not the thickness? Perhaps I'm diverging a bit of the issue here but I do find the MOM variable name bit cryptic. I thought ht is the cell's depth at the t-cells so their differences give the dzt?

[taimoorsohail]

Variables like temp have a thickness defined by dzt, which at the bottom is aligned with ht, not st_edges_ocean. They're just output on the st_ocean grid for ease of saving.

So, to clarify, the st_ocean dimension in temp is incorrect, and to be completely accurate, temp actually maps onto a variable vertical grid defined as the vertical cumulative sum of dzt?

What is ht if it's not the thickness? Perhaps I'm diverging a bit of the issue here but I do find the MOM variable name bit cryptic. I thought ht is the cell's depth at the t-cells so their differences give the dzt?

I think ht is a 2D field that represents to total column thickness at a given lat/lon (i.e., the sum of dzt).

[adele-morrison]

So, to clarify, the st_ocean dimension in temp is incorrect, and to be completely accurate, temp actually maps onto a variable vertical grid defined as the vertical cumulative sum of dzt?

Yes that's correct.

[adele-morrison]

I think it would be ok to ignore the variation in vertical position of cells above the bottom, because that doesn't vary very much. But binning using ht/hu would be good.

[taimoorsohail]

Thanks, I'll work on this and get back to you.

[navidcy]

No pressure, no need to promise! The issue is up for grabs.

But when you actually start working on it a good idea is to assign yourself this issue so that nobody else starts doing double job.