A Comprehensive Look at Neptune's Wind Field and Cloud Structure from Multi-Wavelength Observations

Near-infrared and visible images of Neptune are sensitive to the visible cloud deck, located at the methane condensation level P < 1.5 bar. These observations can be used to track the velocities of bright cloud features at different latitudes from which a smooth zonal wind profile can be generated. However, individual features can be dispersed from the smooth profile by more than 200 m/s, thus hinting that Neptune's zonal wind profile may be more structurally complicated. This dispersion may be explained by wave propagation, unseen vortices, and rapid alterations in cloud morphology. Vertical wind shear is another important factor. Keck observations in the H and K' bands reveal wavelength and depth dependences on the zonal wind profiles. At the equator, cloud features probed in the H-band are, on average, 100 m/s weaker in wind speed strength and deeper than those seen in the K' band (Tollefson et al. 2018). The drift rate of Neptune's dark spots, believed to be anti-cyclones, are intrinsically linked to this background wind field and wind shear. The dark spots are visible at UV wavelengths and provide a localized look into the atmosphere below the cloud deck. SDS-2015 is the most recently discovered dark spot, lying at P >= 3 bar, near the H2S cloud deck (Tollefson et al., 2017, Wong et al., 2018). If dark spots are Kida-type vortices, then the drift rates and morphology of SDS-2015 can be used to infer the wind shear near the H2S cloud deck. Combined, these observations provide a comprehensive look at Neptune's zonal wind field and cloud structure over several scale heights.