Floating point sum errors with longitude normalization in MONET

[rschwant]

There are some small floating point sum errors with the longitude normalization in MONET that impact the pairing step in MELODIES MONET namely for the vertical interpolation we need to pick the right value based on the exact values for latitude, longitude, and pressure_obs. These longitudes are not the same in Python speak: 120.711744 and 120.71174400000001. The result is for some datasets (e.g., first noticed with the ASIA-AQ data) there are a lot of NaNed values when doing the pairing step.

We will document how we are fixing this here in case it comes up again for other datasets.

[rschwant]

Zach is working on a fix in MONET here for this: noaa-oar-arl/monet#160