Complex changes are occurring in the South Temperate Domain at present, on both sides of oval BA and up to the GRS.  These may be important stages in the cyclic birth and death of large-scale structured sectors of the domain.  In recent months we have been anticipating the culmination of the latest cycle, and the start of another.  The former refers to the arrival of the cyclonic structured sector known as the STB Spectre at the f. side of oval BA; the latter refers to the origin of putative new cyclonic circulations on the p. side of oval BA.  

In summary:  The p. end of the Spectre caught up with STB segment A (the dark patch f. oval BA) in mid-Feb., 2020, or somewhat earlier.  There has been no noticeable change in the Spectre itself, which has remained invisible to ground-based imaging except at its f. end.  However, from early March, segment A itself has been expanding again and remains turbulent, and all the other expected sequels of such a collision have occurred: the acceleration of oval BA, the dark collar around BA (which already existed), the outbreak of dark spots Np. BA in the STBn jet (which started in Dec.), and the outbreak of dark spots Sf. into the ‘tail’.  

On previous occasions it was suspected that all these phenomena could be due to the turbulence in segment A, which was renewed each time another structured segment merged with it.  In 2020, the STB Spectre had become so long that one could not confidently forecast whether its collision would have the same consequences. The result seems to have been that it has not undergone any transformation itself (at least, not yet), but since the collision segment A itself has expanded with renewed activity, thus producing the same consequences around it.

This report describes the situation as seen in JunoCam images during solar conjunction, and in amateur observations since.  Thanks are due to the observers who have produced excellent images, mainly in Australia and South Africa and the Philippines.  Thanks are also due to Shinji Mizumoto of ALPO-Japan, who makes regular maps that are an invaluable resource; and to the JUPOS team, whose data have provided drift rates for the features (here expressed as DL2 (deg/mth), i.e. degrees in System II longitude per 30 days).

JunoCam obtained good views of the region of interest at PJ26 on April 10, which will soon be described in a separate report.

The report (including miniature figures) is here as a PDF:   Report-2020-no2_STempR.pdf

The full-size figures are here in a ZIP file:    Report-2020-no-2_STempR.zip

Figure 5 (below):  Animation of two images taken 10 hours apart on 2020 April 14, showing the region centred on Oval BA; images and animation by Christopher Go (Philippines) and E. Sussenbach (Curaçao).