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[python #PPS-589228]: metpy units don't seem to be correct

Hello, and thanks for reaching out!

Good catch! This documentation is incorrect. In our constants, we define R_v as 
R (in J / mol / K) divided by M_water (in g / mol), resulting in the value you 
received in J / g / K. We'll fix this to either document correctly, or update 
the definition of R_v to return J / kg / K.

Either way, useful tools for you here are Pint's unit conversion methods, 
particularly `.to('<unit>')` (docs: 
https://pint.readthedocs.io/en/stable/tutorial.html#converting-to-different-units).
 So, for you here,

  Rv = mpcons.water_gas_constant.to('J / kg / K')

which will do the appropriate multiplication and update your Quantity's unit 
string. This can also be found in MetPy's units tutorial 
(https://unidata.github.io/MetPy/latest/tutorials/unit_tutorial.html#converting-units).
 Thanks again for reaching out, and let me know if there's any further help we 
can provide!


All the best,

Drew


> For the water_gas_constant, the documentation says that units are J/K/Kg 
> however:
> 
> Rv=mpcons.water_gas_constant
> 
> This returns:
> >>> Rv
> <Quantity(0.461523116, 'joule / gram / kelvin’)>
> 
> Note the units are J/g/K. I would have expected it to return 461.52 J/kg/K
> 
> Other constants (e.g. dry_air_gas_constant) are correct. How do I convert it 
> to J/kg/K? Obviously I can multiply by 1000 but that does nothing for the 
> units.
> 
> The units documentation doesn’t cover a case like this.


Ticket Details
===================
Ticket ID: PPS-589228
Department: Support Python
Priority: Low
Status: Closed
===================
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