Jupiter’s South Temperate Domain, 2015-2018

John Rogers* (2019 Feb.)

THIS COMPREHENSIVE REPORT IS ATTACHED HERE:

–THE FULL TEXT & TABLES, AS A PDF:    STempR_2015-2018_Report-text.pdf

–THE FIGURES IN MINIATURE, AS A PDF:  STempR_2015-2018_Report-Figures.pdf

–THE FULL-SIZE FIGURES, IN A ZIP FILE:  STempR_2015-2018_Figures.zip

THE INTRODUCTION AND SUMMARY ARE SHOWN BELOW (for references see the full report) with a summary diagram beneath:

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*This report represents results from many observers, and from the JUPOS team, and from the JunoCam team – to all of whom I am very grateful.   The JUPOS team are: Gianluigi Adamoli, Michel Jacquesson, Marco Vedovato, Rob Bullen, Hans-Jörg Mettig, and Grischa Hahn.   The JunoCam team are:  Candy Hansen, Glenn Orton, Tom Momary, Mike Ravine, Mike Caplinger, and Gerald Eichstädt.

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This report describes the changes in the South Temperate domain from 2015 to 2018, as observed in ground-based images and in maps from Hubble and Juno.  The dynamical features and previous history of this domain were described in our previous long-term reports for 1991-1999 [ref.1], 2000-2012 [ref.2], and 2012-2015 [ref.3].  Our final report on this domain for 2014/15 was included as an Appendix in the latter report [ref.3] so is not fully covered here.

Section 1 gives an overview of these three years. 

Section 2 summarises data from cylindrical maps of spacecraft images, which have been plentiful in these years and could be exploited further.  From the Hubble Space Telescope, pairs of maps 10-20 hours apart are made annually by the OPAL project, and single or paired maps have been made on other dates by the WFCJ project.  From Juno, southern-hemisphere maps are made from JunoCam images, usually every 53 days since 2016 August.

Section 3 reviews our ground-based results, all from amateur ground-based images unless otherwise stated.  Most of this information has already been posted in our reports on the BAA web pages, along with many illustrations. 

Appendix A is our new analysis of wind speeds in a cyclonic circulation called the STB Ghost, first in its quiescent state (from Hubble maps), then during its dramatic transformation in 2018 Feb.

Appendix B contains comprehensive JUPOS charts in both L2 and L3.

1.  Overview

This domain is distinctive in its longitudinal segmentation (Figures 1 & 2).  It always has two to four structured sectors (with major cyclonic and/or anticyclonic structures) separated by undisturbed sectors [ref.2].  From 2015 until early 2018, it had no visually striking features.  There was no dark South Temperate Belt (STB), just a whitened domain with three inconspicuous structured sectors (none of them dark), and no STBn jetstream spots.  The three structured sectors were: 

           (1)  Oval BA and the small dark spot f. it.  Oval BA still had its orange colour, usually quite strong.  The dark spot f. it, which had been turbulent and contracting, was small and largely quiescent. With the decline of this spot’s activity, oval BA had decelerated to a speed typical of this quiescent condition.

            (2)  The STB Ghost (STB Structured Segment E).  This was a cyclonic circulation, appearing as a pale blue loop, but methane-dark – just like the former Segment C (STB Remnant).  

          (3)  The STB Spectre (STB Structured Segment F): a duplicate of the STB Ghost.  This arose in early 2015 as a very dark cyclonic spot, which faded to pink in early 2016.  In May it completed its fading to white as expected, leaving just a pale bluish loop around it, which persisted and was methane-dark, like the STB Ghost.  So it was named the STB Spectre.

          The Ghost and the Spectre, although cyclonic, affected the whole width of the domain, and blocked any spots approaching them on the SSTBn jet from the west.  These spots would recirculate anticyclonically, due south of the Ghost or Spectre, and return westwards in the STZ for tens of degrees.  This circulating track became visible as an orange-tinted ‘recirculation loop’ Sf. the Ghost and the Spectre. 

          Typical drift rates [refs.2 & 3], in DL2 (deg/mth) are as follows:

Oval BA when dark spot f. it is quiet: -10.4 to -11.8.

Oval BA with dark turbulent STB f. it: -14.2 to -16.5.

Structured sectors such as STB Ghost and Spectre:  -15.4 to -17.8.

          Their speeds from 2016 January to mid-May were typical:  Oval BA, DL2 = -11.0 (±0.5) deg/mth, though with some fluctuations;  STB Ghost and Spectre, both DL2 = -16.4 (±0.3) deg/mth, and therefore moving towards oval BA.  From mid-2016 June to early 2018, BA had a mean speed of -12.0, with ~2-month oscillations, while the Ghost and Spectre proceeded with typical speeds.

Two dramatic events affected the domain in early 2018.  Coincidentally, both began on 2018 Feb.4:

i)  The STB Ghost collided with the small dark spot at the f. edge of oval BA, as predicted [ref.5], and a bright spot (convective plume) suddenly erupted inside it, initiating a turbulent transformation of the whole Ghost into a chaotic dark STB segment adjacent to oval BA.  This also had all the other effects typical of these collisions, viz. oval BA developed a dark rim and accelerated, and dark spots were emitted p. on the STBn jet and f. in the STZ.

ii)  A South Tropical Disturbance (STropD) arrived at the f. edge of the Red Spot Hollow, and turbulent material from it promptly began streaming around the S side of the GRS.  Much of this accumulated in the S. Temperate domain Sp. the GRS, and a long sector became filled with tiny vortices.  However, this all dissipated by summer 2018, with no lasting effect.

We previously noted that new cyclonic circulations and other spots tend to arise tens of degrees p. oval BA, but in these years, only small transient spots have appeared; no new structured segment has developed.  The present count of two structured segments (the complex with oval BA, and the Spectre) has existed in some previous years, but it seems likely that a new structured segment will appear in 2019 – unless the STB revives more generally in some unexpected manner, as happened in 1993. 

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