Vertical coordinate conversions

[csyhuang]

This issue is brought up by Pragallva - current QGField takes in variables in pressure coordinates, but some model outputs are in $\sigma$/hybrid coordinates.

The current solution without changing the code base is to interpolate variables from $\sigma$ grid to regular pseudoheight grid, and then input to QGField the corresponding pressure grid: plev = P_GROUND * exp(-pseudoheight/scale_height).

Additional functionalities to incorporate to QGField in the future:

• (quick) Allow the option to skip vertical interpolation if variables are already on a uniform vertical pseudoheight grid
• (need work) Incorporate sigma-to-pseudoheight interpolation of variables into QGField

Thanks Pragallva for the discussion 😄