Use pint to properly deal with unit conversions in "Barotropic streamfunction" example

[navidcy]

This PR showcases how we can use pint to properly deal with unit conversions e.g. when we want to convert from mass to volume transport or when we want to convert from m^3/s to Sverdrup.

There are heaps of warnings that xarray spits out and

import warnings
warnings.simplefilter(action='ignore', category=UserWarning)

at the beginning seems to have no effect... I don't know how to remove them or what do they are really trying to say (I mean, I can read them but I don't know what I should do...). If anyone has any idea is welcome!

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[navidcy]

I removed the warnings by passing chunks={'time': 3}) to the cc.get_variable.

[navidcy]

@julia-neme, I don't know if it was you who defined the shift_colormap(). I deleted the shift_colormap() since it was never used! feel free to put it back and use it if you like! :)

[lidefi87]

Sorry for the delay in getting back to you. I was flat out this week, and thanks again for being on top of keeping the examples up to date.

I checked the notebook and it runs, but if I am honest, I do not really understand what it does because I do not know what a barotropic streamfunction is. Perhaps it would be clearer to a physical oceanographer, which I am not.

I do have a question/request. Is it important to highlight positive and negative values in the map? At the moment is a continuous colourmap and I cannot distinguish positive from negative values. If this is important, maybe a divergent colourmap would be more appropriate (maybe the delta palette from cmocean, which has blues/yellows/green).

If it is not important to make this distinction, let me know and I will approve it so this can be merged.

[navidcy]

hi @lidefi87! the stream function is a quantity whose derivatives give you the velocities... thus its actual value is irrelevant, only its gradients matter. you can think of it like pressure.

the colormap was actually a divergent one but because it was highlighting the value ψ=0 as a "special one" I decided to change to this non-diverging colormap.

[lidefi87]

Ah. Got it now. Thanks for explaining it. I'm approving it now 😊