[11]  NEBn:  Interim reports on the SSTB (cyclonic white ovals break up) and STB (A remnant or a forerunner?)   (Reports,  2006 July 30)

SSTB:  AWOs persist, cyclonic white ovals break up.

The set of S.S. Temperate anticyclonic white ovals (AWOs) continues to be an eye-catching feature of hi-res images: in order, A8-A0-A1-A2-A3-A4-A5.  The attached image set shows this array in 2006 June and July. 

Most or all of them are separated by cyclonic circulations, which are more variable in appearance. In these image there are two main types: white ovals (which tend to expand in length forming white lozenges, as has occurred between A2-A3 and between A4-A5), and folded filamentary regions (FFRs, which are like miniature versions of the rifted regions in SEB and NEB, and are hard to detect in ground-based images). The best images can now distinguish these cyclonic features and document their transformations. 

In this series, a small white oval between A0-A1 disappears suddenly between June 5 and 10, becoming a FFR; actually it probably merges into a pre-existing FFR f. it.  Then note the long, long-lived white lozenge between A2-A3, which seems to have lower contrast from June 8 onwards but is still present on July 2; but in the next images, July 21 and 26, it too has broken up to form a FFR.  It may be significant that this happened as it was passing the STB Remnant (see below), which could destabilise the adjacent SSTB; perhaps the cyclonic white lozenge between A4-A5 will do likewise in a few months' time.  These white lozenges tend to expand (like their equivalents in the STB: see my book pp.54 & 231), perhaps pushing the adjacent AWOs apart, and as the white lozenge broke up, oval A3 immediately rebounded from oval A4, to which it had been uncomfortably close.

STB:  A remnant or a forerunner?

The STB Remnant (seen in the same images) is an obscure faint bluish streak in otherwise whitened STB latitudes, but I think it is important.  From its latitude and appearance, it is probably a cyclonic disturbance, perhaps like a FFR. It thus constitutes an active complex in the STB, approximately half way round the planet from the other such complex; but it has no large AWO.

This second complex is essentially an 'orphan' cyclonic circulation such as those observed by the Pioneer and Voyager spacecraft (see 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 three great AWOs.  In the late 1980s, the STB became divided into two, with one complex containing AWOs BC + DE, and the other containing oval FA.  When they all combined into one complex, new spots arose to create a second complex which existed from 1998 to 2003. (This is the situation shown in the Cassini movie.) When it too merged with the first complex (now characterised by the single AWO  BA), new spots again appeared on the other side of the planet, and these have persisted as the present STB Remnant.

In summary, there must always be 2-4 active complexes spaced around the S. Temperate domain. If there is a large gap, a new feature arises to maintain the spacing, often an orphan cyclonic circulation.

But we are also waiting for another phenomenon to occur.  As there is only one great oval left, will the S. Temperate domain again become subdivided into several large anticyclonic cells which contract to form a new generation of great AWOs, as happened from 1940 onwards (see book pp.223-228)?  The first sign of that happening was the appearance of three short dark features (dusky STZ or STB(S)), subdividing the STZ. This could describe the appearance of the two active complexes in the present STB!  They do not have the circulation patterns expected for the origin of great anticyclonic circulations (see the Cassini movie): but could they be the fore-runners of the same process?  Time will tell.

John Rogers, 2006 July 30