We present 2.03-2.30 \mu m near-infrared spectroscopy of Neptune taken 1999 June 2 ( UT ) with the W.M .
Keck Observatory ’ s near-infrared spectrometer ( NIRSPEC ) during the commissioning of the instrument .
The spectrum is dominated by a bright cloud feature , possibly a storm or upwelling , in the southern hemisphere at approximately 50 \fdg S latitude .
The spectrum also includes light from a dimmer northern feature at approximately 30 \fdg N latitude .
We compare our spectra ( \lambda / \Delta \lambda \sim 2000 ) of these two features with a simple model of Neptune ’ s atmosphere .
Given our model assumption that the clouds are flat reflecting layers , we find that the top of the bright southern cloud feature sat at a pressure level of 0.14 ^ { +0.05 } _ { -0.03 } bar , and thus this cloud did not extend into the stratosphere ( P < \sim 0.1 bar ) .
A similar analysis of the dimmer northern feature gives a cloud-top pressure of 0.084 \pm 0.026 bar .
This suggests that the features we observed efficiently transport methane to the base of the stratosphere , but do not directly transport methane to the upper stratosphere ( P < 10 ^ { -2 } -10 ^ { -3 } bar ) where photolysis occurs .
Our observations do not constrain how far these clouds penetrate down into the troposphere .
We find that our model fits to the data restrict the fraction of H _ { 2 } in ortho/para thermodynamic equilibrium to greater than 0.8 .