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Jupiter’s North Equatorial Belt (NEB) shows a wide variety of impressive phenomena, but the relationships between them are still largely mysterious. Here we summarise the range of speeds shown by NEB rifts from 1986 to 2011, and consider how rifts relate to NEB expansion events, which occurred six times during those years. BAA and JUPOS records for rift speeds in those years largely fall into two ranges: ‘fast’ with DL2 = -2.9 to -5 deg/day, and ‘slow’ with DL2 = -1.0 to -2.8 deg/day. These confirm the two distinct ranges found in the historical record, Fast drifts are found in most years, whereas slow drifts (shown by more northerly rifts) are found only just before, during, and after a NEB expansion event. Slow rifts always appear at the onset of an expansion event, though one arose shortly before. When the expansion is completed, there may be no remaining large-scale rifts, or slow rifts may continue to appear until the NEBn recedes again. Thus a slow rift, which includes a convective plume, is always present at the start of a NEB expansion event, and could be the initiating factor, although it is also possible that the slow rift is only one among several phenomena induced by an unknown cause. This contributes to our developing view that NEB expansion events affect the whole belt and are comparable in many respects to SEB Revivals.

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John H. Rogers, Ph.D.
Jupiter Section Director,
British Astronomical Association

John H. Rogers, Ph.D. Jupiter Section Director,
British Astronomical Association
jhr11@cam.ac.uk
http://www.britastro.org/jupiter/