Potential bug in geopotential to height

[Marston]

import metpy.calc
from metpy.units import units

height = np.array([10000]) * units.m
metpy.calc.height_to_geopotential(height)
see image 1
----
gph = np.array([80000]) * units('meter ** 2 / second ** 2')
metpy.calc.geopotential_to_height(gph)
see image 2

According to the docs, the height and gph should be without a few percent of each other at high altitudes. But here it is off bya factor of ~10. I believe this is a bug.

[dopplershift]

Note the difference in units there, geopotential, as a sort of mass-normalized potential energy cannot be compared directly to height. At a bare minimum you need to divide by gravity. In doing that, you'll see that you get 9984 vs. 8168, which is still not close--but I don't think 8km classifies as "high altitude".

Also, where in the docs did you see the part about them being within a few percent at high altitude? I'd like to see if there's something we should clarify.

[Marston]

My bad, I mixed up geopotential (gp) and geopotential height (gph).
I looked of the equation in Meteorology science and engineering 2015 Eq 1.14b. The height and gph are suppose to be close to each other at high altitudes.

[dopplershift]

I got ya, you mentioned "according to the docs" so I assumed you meant meant the MetPy docs, but I follow now. Those should be similar at high altitude, but my rough guess is that they're "close" at something ~100km.