Improve definitions and usage of "surface" vs "surface_adjacent_layer" for wind variables, as well as "direction"

[mkavulich]

Description

As discussed in issues #151 and #153, there are shortcomings in both the names and definitions surrounding near-surface wind. This PR implements the changes discussed in those issues:

• wind_at_surface variables are now wind_at_surface_adjacent_layer
• We now have wind_to_direction in addition to wind_from_direction
• direction is given a definition in the rules

Issues

Resolves #151, #153

[jianjunj]

@mkavulich Can you confirm that "wind_at_surface_adjacent_layer" is "wind at the lowest model layer" ?

[jianjunj]

@mkavulich Can you confirm that "wind_at_surface_adjacent_layer" is "wind at the lowest model layer" ?

I see. It is.

[svahl991]

Could we also look to see which wind *_at_surface_adjacent_layer names do not have a corresponding *_at_10m name, and add them where necessary? Then they're there if/when we need them.

[svahl991]

@mkavulich Can you confirm that "wind_at_surface_adjacent_layer" is "wind at the lowest model layer" ?

FWIW, I've encountered someone else who finds the "surface adjacent layer" wording more confusing than "lowest model layer". Personally, I don't have a problem with either one, and think both are better than the "at surface" being replaced. I don't know if I consider it worth changing, but I thought I'd mention it.
https://github.com/JCSDA-internal/ufo/issues/4313#issuecomment-5352176745

[svahl991]

Tagging @ClaraDraper-NOAA @BenjaminRuston @BenjaminTJohnson @mikecooke77

[mkavulich]

@svahl991 I'm unable to view the JCSDA internal repository, so let me know if there's any specific context I'm missing.

The surface_adjacent_layer wording has been in use for many years in CCPP, so I'm hesitant to change it without thorough discussion, but I won't reject the idea offhand. Expanding my usual "atmospheric thinking" into the ocean I can see how there may be some strangeness/ambiguity there, since any modeling system that incorporates information underneath the surface would have a different definition of "surface-adjacent" than the atmosphere does. And in fact it seems that we already have at least one standard name that deviates from this standard: mass_content_of_water_in_top_soil_layer. I am not sure if there are any individual models that might incorporate layers both above and below the surface, but if that existed that would for sure be a deal-breaker for keeping the current wording.

That said, I can also envision scenarios where "surface-adjacent layer" is not synonymous with "bottom layer of atmosphere". For example, an atmospheric state interpolated to pressure coordinates can easily have "layers" that are below the physical surface (I clearly remember this scenario giving me fits in my masters thesis work!). In that case, if we did decide to change the wording, something like "atmospheric layer immediately above the surface" would be required.

I will bring this up for wider discussion at next week's meeting.

[svahl991]

To be clear, I realize changing the surface_adjacent_layer terminology would be a pretty big change, and I personally don't think it's worth it, and feel the wording is clear enough, and there are much bigger fish to fry.

But here's the PR comment you couldn't follow the link to. It came in the context of a discussion of making the name changes that are in this PR within JEDI code. It was similar to @jianjunj above, so I just wanted to mention it.

To be frank, wind_speed_at_surface_adjacent_layer (unclear what "surface adjacent" means) is confusing to me as well.
Is it just the "wind_speed" at the lowest model level?
Then, will wind_speed_at_lowest_model_level be more clear?