[ncl-talk] error in pot_temp_equiv

[Buzan, Jonathan R]

Hi NCL-Talk,

I was checking out the pot_temp_equiv function in NCL.  Unfortunately, I believe I found an error.  https://www.ncl.ucar.edu/Document/Functions/Contributed/pot_temp_equiv.shtml
The descriptions page states it uses Davies-Jones (2009) for the calculation.  However, looking at the contributed file, the code uses Stull 1988 §13.1 p. 546, which does not use the lifting condensation temperature.

I use Bolton 1980 equation 22 for lifting condensation temperature and equation 39 for equivalent potential temperature.
Using typical warm pool values, T = 27°C-31°C, and an average humidity 75% at 1000mb:

NCL: pot_temp_equiv = 69.1°C, 72.7°C, 76.4°C, 80.3°C, 84.3°C
Bolton Eqn 39  = 77.8°C, 82.2°C, 86.9°C, 91.8°C, 97.0°C

These are substantially different values for the warm pool.  This is important for researchers analyzing buoyancy differences for tropical disturbances.

-Jonathan R. Buzan


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