Computer Science
Scientific paper
Sep 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993icar..105..110s&link_type=abstract
Icarus, Volume 105, Issue 1, p. 110-141.
Computer Science
33
Scientific paper
We used Voyager 2 images of Neptune to investigate the dynamics of the Great Dark Spot (GDS), the Scooter, the Second Dark Spot (DS2), and the South Polar Features (SPF). Relative to previous studies, we covered a longer time base, achieved more complete sampling of the available data, and improved accuracy by using stars to correct navigation errors. We tracked the GDS 8-day shape oscillation for more than 2000 hr, measuring amplitudes of 7.4° in longitude and 1.5° in latitude. We found a surprisingly large increase in the mean latitudinal size of the GDS from 8° in January 1989 to 17° in August. During the same period, we measured steady GDS northward motion from 26°S to 17°S and found no evidence of the latitudinal limits. We confirmed that the varying longitudinal drift rates of the GDS and DS2 were simple functions of latitude that approximately match the zonal wind profile. Measurements of at least three cycles of the periodic motions of the DS2 defined a 36-day period and amplitudes of 2.4° in latitude and 47.5° in longitude relative to its mean drift longitude. We found that the bright core of the DS2 varied in step with the DS2 latitudinal oscillation, reaching a maximum area when the DS2 was furthest north. A large increase in relative core brightness at high phase angles is consistent with forward scattering cloud particles. We measured one cycle of a Scooter longitudinal oscillation of 20° about its mean drift position, with a period of 120 days; but the Scooter's latitudinal motions are too small and of the wrong frequency to be consistent with an advective model of the zonal motions. We found that the highly variable SPF formation region has the same mean longitudinal drift rate as the DS2, but an offset of 180° in longitude and a 20° difference in latitude. The apparent synchronization of these widely separated and dramatically different features is unexplained. Coupling to the deep interior is ruled out by the significant difference between the radio and cloud periods. Observed motions of all features are described by empirical models valid over the Voyager time period. Comparisons of Voyager results with groundbased observations did not lead to conclusive constraints on the long-term dynamics, although much of the data seem to be consistent with a 5.8-year oscillation in GDS latitude.
Fry Patrick M.
Limaye Sanjay S.
Sromovsky Lawrence A.
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