[7]  S. Temperate domain: reddened oval BA, and the other circulating complex  

  Thoughts on the redness of oval BA:

  Oval BA is the last survivor or a series of 3 great storms along one belt, which merged together a few years ago. Up until a year ago it was white. But at the start of 2006 it was clearly reddish – first reported by Christopher Go (Philippines) on Feb.24.  Other images showed the colour had been developing since December.

The colour has become even more prominent since, in an orange ring within the oval.

Now it is about to pass the GRS.

(See Chris Go's special web page:)  http://www.redspotjr.com

  Here too are some thoughts on the reddened oval BA and its forthcoming passage past the GRS (conjunction forecast for mid-July).  They will, of course, not collide nor be disrupted.  Oval BA, like its predecessors on the STB, passes the GRS about every two years.  However structures in the STB are sometimes destabilised as they pass the GRS: for example, these 'white' ovals have sometimes appeared slightly reddened or veiled,  and segments of STB have either darkened or faded. So we might see changes in the appearance of oval BA and of the dark STB f. it, during the passage.  Whether its redness will change is anyone's guess!

The colour in the GRS is always strongest when the SEB is faint (whitened) – as last seen in early 1993.  Although large sectors of the STB are often faint (as now p. BA), this has long been a common event and  does not seem to resemble the fading of the SEB. Nevertheless, it will be interesting if there are correlated changes in the colour of oval BA and of the surrounding STB after it passes the GRS.

It is interesting that the reddish colour has appeared as a ring within the white oval BA (possibly around its radius of highest wind speeds?—we await the analysis of Hubble images).  The GRS also may have developed reddish colour first as a ring, in the 19^th century.  From its discovery in 1831 up to 1856, only the light Hollow was seen.  In 1857 a dark arch appeared around its S side. Then when the SEB was faint in 1858/59, and again in 1870, it was drawn for the first time as a dark ring. In 1870, this was described as a 'ruddy elliptical line' by one observer (Mayer). As he used only a 15-cm refractor, I would not trust the colour, but this was the first mention of reddish colour in it.  The reddish colour was first clearly seen, filling the Spot, by Rosse and Copeland in 1873.  I suspect that these observations traced the true origin of red colour in the GRS, and that oval BA may be recapitulating this development now.  (Or it may just be going through a funny phase.)

Reddish colours on Jupiter may be associated with high vorticity, ranging from the GRS, to tiny  eddies in cyclonic 'rift' regions in Voyager images. We still don't  know why only some anticyclonic ovals become reddish and methane-bright –especially in the NNTZ (e.g. the present LRS, methane-bright in the Lazzarotti-Olivetti image of April 10).  Reddish colours over belts or zones are also associated with recent energetic outbreaks (e.g. a segment of NNTB is reddish following last year's numerous NNTBs jetstream spots, and the NEB was recently reddish after the broadening event).  It is still not clear whether these disparate phenomena really share any physical properties, but they all appear to involve high vorticity or high energy in some form, and to lead to the appearance of reddish haze over the clouds.

The two dynamic complexes in the South Temperate domain:

In the S. Temp. domain, the STB since 2000 has more long-lived circulations than just oval BA.  BA is part of a complex with cyclonic turbulence following it plus another, small AWO: in white light there is a dark belt segment which tapers southwards on the f. (W) side. On the other side of the planet, there is a similar dark belt segment which tapers southwards on the f. (W) side; but this second complex contains no substantial AWO. 

The arrangement is described in our BAA report for 2000/01 (as previously referenced). At that time, the second complex was a substantial dark belt segment, which we originally called Dark Spot 2, but that one eventually merged with the STB f. oval BA.  Then a new little streak appeared in the vacant region of S. Temp. domain.  This new second complex is visible only as a faint blue streak (alongside SSTemp-AWO-A1 in 2006 March, alongside A2 now in early May); but its existence implies a long-lived cyclonic circulation still exists.

This second complex is essentially an 'orphan' cyclonic circulation such as those observed by the Pioneer and Voyager spacecraft (see my book p.228).  In those days, in addition to the 3 widely spaced AWOs, the orphan cyclonic region divided the STB into four.  At other times the STB was just divided into three by the 3 AWOs.  In the late 1980s, the STB was divided into two, with one complex of AWOs BC + DE + others, and a second complex containing oval FA (book p.221).  Now the STB is again divided into two.

John Rogers, 2006 May 18