[9] The GRS and adjacent jets: Further analysis of amateur images, 2013/14

Summary
 
This report describes the GRS and STBn jet up to 2014 April, when they were viewed by the Hubble Space Telescope.

1. Shrinkage of the GRS
The GRS has shrunk in latitude as well as longitude – slightly over many years, and considerably in 2013/14, in parallel with the shrinkage in longitude.  This is the first definite change recorded in latitudes for the GRS.  The centre latitude did not change significantly until 2013/14, when it is ~0.2º further south.
These recent changes in the GRS are not due to the incoming STBn spots, because detailed study of the STBn outbreak shows that the spots did not reach the GRS until 2013 Dec., long after the GRS had shrunk.
 
2. Circulation of the GRS
Measurements of hi-res images in 2014 Feb., tracking a dark grey streak round nearly 3 circuits inside the GRS, show a slightly varying rotation period of 3.6 to 3.8 days, confirming our measurement in Jan.  The hi-res images in 2014 Feb. have been compiled into (i) a series of maps, (ii) measurements of the internal rotation of the GRS, (iii) an animation of the maps showing the interactions with STBn jet spots. 
The images in 2014 April, spanning the time of the HST imaging, have also been compiled but there were no persistent trackable features within the GRS.
 
3. The STBn jet outbreak
3.1.   We present a full JUPOS analysis of the STBn jet outbreak in 2013/14.  The jet spots appeared on the STB(N) just p. oval BA; they initially moved comparatively slowly [DL2 ~ -75 to -86 deg/mth], but speeded up to the usual jet speed [DL2 ~ -94 deg/mth] within months; their zonal drift profile (ZDP) followed a shallow cyclonic gradient from ~28.5ºS to 27ºS, shifting to higher speed as the outbreak developed; many of the spots drifted north through this range during their lifetimes without change of speed.  In all these respects, the outbreak behaved exactly like previous ones in 2004-2005 and 2010-2011.
3.2.  Interactions with the GRS:  Hi-res image sets are provided for 2014 Feb. and April, showing in detail how the jet spots were distorted and disrupted as they passed the GRS. They were strongly accelerated and deflected south for the duration of the passage.  In some cases, remnants survived, reverting to approx. their original speed and latitude.
3.3.  Interactions with the STB Ghost:  A few STBn jet spots survived to pass the STB Ghost, when they drastically decelerated. (The same was recorded in 2005.)
 
4.  The SEBs jet
The SEBs jet carries sparse, small white spots. In 2013/14 they appear to be vortices with peak jet speed running slightly south of the nominal jet peak, as in most other years.  Although there was anomalous behaviour in autumn, 2012, with exceptionally rapid retrograde speeds, there has been no long-term change in the behaviour of this jet.
 

PDF of text (inc. tables)

PDF of figure legends with miniature figures
ZIP file of full-size figures
MP4 animation of GRS maps  by Michel Jacquesson {GRS-maps-reduced.mp4}

Best Wishes,

John

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