Dynamic Meteorology of Neptune

Abstract

Although Earth-based observations provide hints of Neptune's dynamic activity, most of the observations of cloud patterns, winds, and horizontal variations in temperature are from Voyager. The wind speed varies from 400 m s^(-1) westward at the equator to 250m s^(-1) eastward at -70° latitude. As on all the giant planets, the winds decay with height in the stratosphere. The meridional contrasts in temperature are small in the upper troposphere and lower stratosphere, with mid-latitude minima that are reminiscent of those on Uranus. The oscillations and motions of Neptune's large spots are more regular than those of Jupiter and Saturn. During the Voyager observations, the Great Dark Spot moved steadily equatorward while it oscillated in shape with an 8-day period. The latitude and longitude of Dark Spot 2 oscillated with a 36-day period. The small elements within each major feature appeared and disappeared in less than a day. Such activity is remarkable for a planet whose emitted power per unit area is 1/20 that of Jupiter and 1/400 that of the Earth. Weak viscosity can account for the decay of winds in the stratosphere, and models without viscosity can account for the spot oscillations. But the wind velocities and temperatures vs latitude--especially the differences among the giant planets--have not been explained. Major unknowns concern convection and latent heat release, the interaction with Neptune's fluid interior, and the importance of internal energy relative to solar energy in driving the circulation.

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