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We present H-band (1.4-1.8 µm) images of Neptune with a spatial resolution of ∼0.06 , taken with the W.M. Keck II telescope using the slit-viewing camera (SCAM) of the NIRSPEC instrument backed with Adaptive Optics. Images with 60-second integration times span 4 hours each on UT 20 and 21 August, 2001 and ∼1 hour on UT 1 September, 2001. These images were used to characterize the overall brightness distribution on Neptune, and to determine rotations periods (which translate into wind speeds) of individual cloud features.The images show that the spatial brightness distribution of cloud features, in particular the bright bands at midsouthern latitudes and near 30°N, changed considerably between 1989 (Voyager era) and 2001. The brightest features extend latitudinally over several degrees, and despite the different velocities in different latitude bands, these bright features remain coherent. We show that these features are bright in part because of the foreshortening effect near the limb, which suggests that the features may be composed of small bright clouds that happen to line up near the limb.At certain latitudes (mid-southern and northern latitudes), there is considerable dispersion in relative rotation periods (and hence zonal velocities) of faint and moderately

We report on observations of Neptune from the 10-meter W.M. Keck II Telescope on June 17-18 (UT) 2000 and August 2-3 (UT) 2002 using the adaptive optics (AO) system to obtain a spatial resolution of 0.06 arcseconds. With this spatial resolution we can obtain spectra of individual bright features on the disk of Neptune in a filter centered near 2 microns. The use of a gas-only, simple reflecting layer radiative transfer model allows us to estimate the best fit altitudes of 18 bright features seen on these 4 nights and to set a constraint on the fraction of hydrogen in ortho/para equilibrium. On these nights there were three main types of features observed: northern hemisphere features in the range from +30 to −45 degrees; southern hemisphere features in the range from −30 to −50 degrees; and small southern features at −70 degrees. We find that the altitudes of the northern features are in the range from 0.023-0.064 bar, which places them in Neptune's stratosphere. Southern features at −30 to −50 degrees are mainly at altitudes from 0.10 to 0.14 bars. The small features at −70 degrees are somewhat deeper in the upper troposphere, at 0.17 and 0.27 bars. This pattern of features located at higher altitudes in the northern hemisphere and lower altitudes in the south has also been noted by previous observers. The best fits for all the observed spectra give a value of 1.0 for the fraction of hydrogen in ortho/para equilibrium; the value of the helium fraction is less well constrained by the data at 0.24. We suggest that the southern mid-latitude features are methane haze circulated up from below, while the −70 • features may be isolated areas of upwelling in a general area of subsidence. Northern bright features may be due to subsidence of stratospheric haze material rather than upwelling and condensation of methane gas. We suggest that convection efficiently transports methane ice clouds to the tropopause in the Southern mid latitudes and thus plays a key role in the stratospheric haze production cycle.

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