John Rogers,
British Astronomical Association

Thanks are due to all the observers who have sent images, and to Hans-Joerg Mettig and the JUPOS team for producing an interim set of charts in April, and to Michel Jacquesson, Marco Vedovato, and Yuichi Iga for producing their own maps, analysis, and discussions. The following account uses information from the JUPOS charts, but latitudes are simply estimated. (Also I have not checked histories of single spots before 2006.)

SPR: There are 2 white ovals at ~60 deg.S. Both have been tracked at least since 2006.

SSTZ & SSTB: Yet another small anticyclonic white oval (AWO) has appeared (probably the one labelled A7. though it could be A8), bringing the total to nine. Most of these have lasted for many years, but with some mergers and some new appearances, they are now numbered A0 to A8. Closed cyclonic circulations (white bars) between A1-A2 and between A4-A5 have continued to expand as usual, forcing these AWOs apart. A cyclonic white oval f. A6 is also expanding. Between the other pairs of AWOs, cyclonic 'folded filamentary regions' can be discerned.

STB: Oval BA still contains an orange annulus although it is much fainter than a year earlier, having faded last summer. It is soon to pass the GRS (as happens every 2 years) and the appearance of the belt segments around it often changes at this time. As usual, f. oval BA is the only dark segment of STB. About 120 deg. f. it is the second major long-lived circulation complex, the cyclonic 'STB Remnant', very pale blue.
STropZ: The excitement continues, as the unusual eddying tendency that developed in summer 2006 has taken on another novel form. Instead of the two STrD's of 2007 there are now two dark anticyclonic ovals, slowly prograding. 'Oval 1' may be derived from STrD-1, but indirectly; it is probably the big dark anticyclonic oval which formed at L2=261 on 2007 Sep.1 from merger of all the spots that had recirculated onto the STBn jet. 'Oval 2' may be derived either from the same source, or from circulation flanking STrD-2. Remarkably, as T. Akutsu noted on March 1, it is bright in methane and annular in near-IR; and hi-res visible images show it as Little Red Spot, with a red core and bluish dark rim (first shown by A. Wesley on March 2). The only previous example of a prograding LRS in the STropZ was in 1986, which also arose out of a STrD; and there was probably a similar example in 1889-1890 (see my book pp. 200 & 206). This LRS has just been overtaken by reddish oval BA, and both are approaching encounter with the Great Red Spot. We watch keenly to see what will happen.

The GRS, at L2 = 125 (May 1), has (surprisingly) not been visibly affected by the SEB fading and revival. It is still a well-defined symmetrical orange oval.

SEB: While the SEB is fully restored after last year's Revival, it is still highly disturbed, with rift activity arising in 3 sectors (though prograding to encompass most of the belt). They are:

(1) F. the GRS: the site of the Revival outbreak in 2007, and of perennial activity in normal times.

(2) A mid-SEB outbreak first reported by Wesley on 2008 March 8, immediately p. the GRS (L2 = 100). There had been a stable pale white spot up to then, but on March 8 it erupted as a brilliant white spot, and proceeded to expand and proliferate in classic style. This outbreak is as unexpected as last year's. It may be significant that the SED was passing just as it appeared, and on March 13 the expanding, twisting mid-SEB outbreak connected briefly to the SED as a rift, such as often appears when the SED has just passed the GRS. The approach of the SED may have actually triggered the mid-SEB outbreak: in 1975 there was evidence that secondary SEB outbreaks were triggered by a feature that may have been a SED, and the 2007 outbreak also appeared as the SED was approaching that longitude though it was not so close. So I suspect this is not just a coincidence. It is also notable that this mid-SEB outbreak appeared immediately p. the GRS: this is very rare. However there have been precedents, most notably the origin of the SEB Revival in 1993.

(3) Another mid-SEB outbreak started soon after, first seen by Chris Go on March 21 at L2 = 258. This probably appeared within a dark 'mini-barge' (like the 2007 SEB outbreak). Further white spots appeared at about the same site on March 29, April 4, 12, 21, and May 1: one every 7-10 days. As usual these expanded and prograded as bright rifts, which soon became continuous with the rifted region f. the GRS. As late as May 13, another bright white spot appeared near the original source, at L2=266, again within a dark mini-barge.

Meanwhile on SEBs, the only distinct retrograding ring had the modest speed of DL2 = +30 deg/mth, and arrived at the Red Spot Hollow on April 8. Conditions prevented adequate imaging of the GRS thereafter, but the spot probably ended up as a white rift seen extending Np. from the northernmost point of the Hollow on April 16-18 (exactly as reported for a previous such event by A. Sanchez-Lavega's group).

Otherwise, SEBs is marked by tangled strings of tiny dark spots without obvious rapid motion. One string is of the 'mini-barges' at ~17 deg.S, DL2 ~ +10 deg/mth; another is of dark streaks in STropZ at ~22 deg.S, DL2 ~ 0. However, close scrutiny of images on May 13-14 shows that a string of tiny dark spots at ~20 deg.S is indeed retrograding at ~ +3 deg/day, so the SEBs jetstream is still operating, although not especially fast.

SEBn/EZ(S): The S. Equatorial Disturbance (SED) has been visible since Feb. as a very bright white bay. It passed the GRS on March 7 and briefly interacted with (or even induced) the mid-SEB outbreak described above. It passed the GRS again on April 29 and then developed its classic form, again connecting with rifts to the mid-SEB outbreak and becoming quite prominent in early May. Its L1 was approx. 250 (Feb.26), 265 (Mar.13), 295 (Apr.7-9), 320 (May 7), indicating DL1 = +30 deg/mth.

EZ(N)/NEBs: The EZ this year has few conspicuous features: all the unusual darkness of 2006-2007 has disappeared, leaving only faint tenuous streaks, which are however very complex and beautiful in hi-res images. There are few large NEBs projections, and these consist of plateaux with generally unimpressive festoons. They are virtually static in L1.

However an interesting novelty is an orange-tinted strip along the north edge of the EZ - apparently colour spilling over from the NEB. In recent years such colour has been seen in individual white bays, but not continuously.

It is worth noting that Akutsu's methane images also show a novel pattern in that northern EZ and southern NEB form a moderate-intensity band between the bright EZ(S) and dark NEB(N). This may be the orange haze, appearing reflective in the methane band. It marks a large-scale change from the previous appearance of the EZ in methane, to be discussed in a later bulletin.

NEB & NTropZ: The NEB is still strongly reddish (as in 2007) and has also acquired numerous small dark barges on the N edge. Both phenomena typically occur about a year after a NEB expansion or rifting event, so we were surprised to see them now. The last expansion event was in 2004, and in 2008, the belt has actually narrowed again.

However, a review of 2007 data shows that, while our attention was diverted elsewhere, there was actually much activity in the NEB: A large, long-lived rifted region grew to encompass one third of the circumference and there were other rifts elsewhere; and with these dynamic rifts in the NEB, plus the extreme turbulence in NTropZ during the NTBs outbreak, most of the barges and AWOs were destroyed. In summer 2007 some new barges did develop, as did the strong reddish colour.

As the NEBn edge has retreated southwards, the barges are on the N edge, often associated with prominent cusps from which festoons curve Np. into the NTropZ - a pattern familiar from previous 'retreat' years such as 1994. There are at least 9 barges (though many are small), and 8 AWOs in NTropZ. Although most are slow-moving in L2, there is still white spot Z (WSZ), revived in brightness and speed since its obscurity in 2007, with DL2 = -11 deg/mth. Some of the barges and AWOs p. it share this rapid drift, and are colliding with others which don't. Most important was the collision of two AWOs p. WSZ, in early April (L2 ~320). Although lo-res obs'ns would have suggested they merged, hi-res images showed they did not! Both AWOs shrank as they approached, especially the Sp. one, which then squeezed S of the Nf. spot, breaking up as it did so, and then disappeared. The tiny remaining spot then drifted to lower L2. All this is exactly what happened when a white oval encountered white spot Z in 2006 June. It shows that the paradigm for mergers of AWOs which we have reported in temperate latitudes (Rogers et al., Icarus, 2006b) does not hold for the NTropZ. In fact, no true merger of AWOs has ever been recorded in this latitude. Theoretical study is needed to understand why these AWOs behave differently.

Another interesting phenomenon was the 'rocking' of the little dark barge on the Sp. edge of white spot Z, during the encounter of the AWOs on its p. side. It might have a period of about 5 days although there were not enough data to prove it.

All the other encounters have been between small (cyclonic) barges, and they probably do merge, according to a pattern previously observed (Rogers et al., Icarus, 2006b), although this has not been clearly observed yet this year because of small sizes and incomplete obs'ns. It is notable that all but one of these interactions are occurring just p. white spot Z, so I imagine that white spot Z is causing them, as with previous mergers of barges. These encounters have been: 1) L2 ~ 110, early April (one partner very small). 2) L2 ~ 290, late April: This pair of barges was just p. the site of the AWOs collision, and presumably were also impelled by WSZ. Although the crucial conjunction was not observed (April 22-28), the appearance on April 29 showed the formerly Nf. barge protruding from the Np. end of the other one, just as in our published examples - but in this case a small fragment actually detached and continued prograding. However the greater length of the surviving barge confirms that a typical merger did take place. 3) L2 ~ 310, mid-May; ) Two further collisions p. WSZ, one involving the 4) L2 ~ 270, late May ) product of merger (2); not yet observed.

NTB: Last year's dramatic NTBs jetstream outbreak (DL1 ~ -160 deg/mth; 'NTC-D') led to the revival of the NTB as a prominent orange belt in the latitude of the NTB(S) component, with paler reddish tint flanking it. In 2008, this orange NTB(S) is still very strong, and a fainter, greyer, sinuous (N) component is present as well, with pale ochre shading between them. Thus the full NTB is now reviving, with continuing reddish colour as an aftermath of the outbreak. (However in Akutsu's methane images the NTB is paler than before, apparently because the orange colour is a high-level haze which masks the usual belt.)

On the NTBs edge are at least 6 pale orange lozenges, each about 8 deg. long. Measurements on 3 of them give a consensus speed DL1 = -78 deg/mth (133 m/s in L3). This is a very important development which gives insight into the deep structure of the jetstream. It is one more parallel with the apparently identical NTB outbreak of 1990: in that case, jetstream spots (anticyclonic vortices) were first seen on NTBs 20 months after the outbreak, with DL1 = -57 ('NTC-C'), and persisted with very similar speed for the next 11 years. Now, with better imaging, we can see (probably, incipiently) similar spots from only 11 months after the outbreak, with the cloud-top jetstream speed still not fully back to normal. The rapidity of the change, together with modelling published by Sanchez-Lavega's group, supports a model in which the jetstream has a permanent speed of at least DL1 ~ -160 deg/mth (170 m/s) below the cloud-tops, but the cloud-top wind speed alternates between this 'NTC-D' speed (when outbreaks driven from below are frequent) and 'NTC-C' speed at other times (sometimes, or perhaps always, when jetstream vortices are present). **I will post a more detailed discussion of this topic soon.**

NNTB & NNTZ: A jet-stream spot outbreak is in progress on the NNTBs: a volley of small dark spots with DL2 = -90 deg/mth. (There had been many such spots in 2006, but they disappeared during the NTB outbreak in 2007.) The NNTB consists of irregular streaks.

In the NNTZ latitude, there are several anticyclonic ovals: two are white (L2 = 45, 250) and one is pale reddish (L2 = 90 on May 9). As usual, this LRS is prograding (DL2 = -12 deg/mth) and methane-bright (Akutsu images). All 3 have been tracked since 2006 or earlier.

I'm not including any more images with this report, but if you want to see image sets documenting any of these phenomena, I could send some (and Yuichi Iga, Marco Vedovato, and Michel Jacquesson have produced some too).

Dear Jupiter observers and enthusiasts,

On 2008 March 1 and 2, interesting new developments on Jupiter were revealed in the first methane image of the apparition (Tomio Akutsu, Japan) and the first v-hi-res colour image (Anthony Wesley, Australia). Processed versions of these images are attached, along with images from one year ago at the same scale for comparison. Items of interest are:

1) Oval BA. Wesley's image confirmed the orange ring is still present but much fainter than a year earlier.

2) The two dark features in STropZ. We first thought these were STrD's persisting from last year, but hi-res images, esp. Wesley's, show that they are actually anticyclonic ovals. 'Oval 1' (L2=242) may be derived from STrD-1, but indirectly; it is probably the big dark anticyclonic oval which formed at L2=261 on 2007 Sep.1 from merger of all the spots that had recirculated onto the STBn jet. 'Oval 2' (L2=176) may be derived from the circulation p. STrD-2. Remarkably, as Akutsu points out, it is bright in methane and annular in near-IR. Consistent with this, Wesley's image resolves it into a reddish core with bluish dark rim - a Little Red Spot! (Thanks to Hans-Joerg Mettig & colleagues for the attached JUPOS chart, & Yuichi Iga for discussion.)

3) The NTB. As previously noted, the revived NTB now consists of a narrow grey NTB(N) as well as the strong orange NTB(S). However in the methane image, the NTB was very dark before the visible revival, and is very light now! The methane images show high-altitude haze. They imply that, before last year's outburst, the haze over the NTB remained thin as determined by the jet streams, in spite of the changes in the visible clouds; but the new orange belt created in last year's outburst itself consists of high-altitude haze. (The same appearances were noted in some of the first methane images ever taken, in 1971, by R.B. Minton at the Lunar & Planetary Lab in Arizona.)

Happy observing!

John

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Hi everyone,

The attached set of images (my last for some time) shows small but interesting bright outbreaks on August 7, in two features that we have tracked for many years:

One is a rift in SEB(N), on the CM at L1=38: this is a revival of the rift in the S. Equatorial Disturbance after it has passed the GRS. (This phenomenon was frequent in earlier years, but in recent months the SED has become a long quiescent white area with no rift. The renewal of the rift might be due to the reappearance of convective activity following the GRS. The SED has quickly resumed its classical appeaarance; will this last?)

The other is a bright white spot on NEBn, near L2=50. This is a revival of white spot Z. (White spot Z is the long-lived fast-moving anticyclonic white oval on NEBn. In 2007 April-May, after the NTB outbreak passed it, it suddenly decelerated and became a ragged grey patch, almost disappearing. Now a bright white spot has popped up in it; this mostly dissipated within a couple of days, but left WSZ as a distinct grey ring with a tiny white core. It adds to my suspicion that WSZ was not a simple anticyclonic oval, but had some characteristics of the equatorial plumes - theoretical modelling would be of interest.)

The images also show interesting slower developments in the belts at these longitudes:
* The NTB is still reddish.
* The SEB(S) is now dark and also reddish. It has extended quietly past STrD-1 and is spreading rapidly towards the GRS; so this sector of SEB will also revive, but peacefully. But the middle of the SEB is almost white.
* The Equatorial Zone is not as dark as it was in recent months.

Best wishes,

John

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Hi everyone,

Here is another compilation of the Circulating Current at STrD-1. Thanks to everyone who contributed. This is probably the last that I can make, as I am going on holiday after Aug.17, and I'll have to ask you not to send any more images after that date.

The recirculation of the jet-stream spots, and their mergers, are continuing spectacularly. Sometimes observers have noted that it looks like a big new oval in the STropZ, but this is just an illusion caused by large spots passing on the opposite jet-streams.

On STBn, spots de and fg have merged, and spots h and i have merged. Spot j was delayed in STrD-1 and probably merged with spot k within it. The big spot L (resolved as a ring after merging with at least 2 spots on SEBs) did its U-turn at STrD-1 quickly. But the next spot, p, was held up in STrD-1 and merged with spot q.

In summary, out of 16 spots that came along SEBs, one small one (c) disappeared, but all the others have recirculated at STrD-1, and merged with each other until only 6 are now left: 5 prograding on STBn, and one (pq) still in STrD-1.

Best wishes,

John

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Jupiter update

Here is an update on the Circulating Current at STrD-1 (July 25-31); plus JUPOS charts showing the drifts of all the relevant spots until late July. Thanks to all the observers, and to Hans-Joerg Mettig and colleagues in the JUPOS team .

The dark spots on the SEBs jetstream are still performing the U-turn at STrD-1. They are quite liable to overtake and merge, thus spots ab, de, and fg, now on STBn, and spot L absorbing faster-moving spots on SEBs. Please see the additional notes on the attached images and charts.

Meanwhile, changes are developing in the SEB between STrD-1 and the GRS. This sector is still very pale p. the GRS (with the blue streak Np. the GRS - typical of the faded state).

But a gradual darkening of SEB(S) has spread f. STrD-1: it began as far back as July 10, and by July 26-28 it was obvious (as pointed out by Guillaume Bertrand and Chris Go). Meanwhile there is a dark spotty section of SEB(N) prograding p. the GRS. The limits of the darkened sectors of SEB(S) and SEB(N) are very ill-defined but they are now overlapping, at L2 ~ 20-30 on July 26-28, and more extensively on August 2.
Meanwhile, near the original source region, the whole SEB has been filled in with small-scale turbulent disturbance, from the GRS (L2 ~ 120) up to the source (L2 ~ 180) (July 14-31). Some small white spots continue to appear near the original source, but also in surrounding regions, and the appearance is no different from the perennial post-GRS disturbance of previous years.

Note that the SED (now a long white area) passed the GRS around Aug.1; will it cause rifting or further disturbance in SEB(N) in the next few days?

John

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Jupiter's Circulating Current, Part 3b

Here is another compilation showing the progress of the Circulating Current. Spots f and g have merged while undergoing the U-turn at the STrD, before emerging on STBn. Spots h,i,j are still entangled in the STrD today. All the spots appear grey when on SEBs but slightly redder when on STBn.

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Also attached is a movie of some of the images in Powerpoint.


Many thanks to everyone who has contributed.

Meanwhile in the northern hemisphere, it is amazing to see the strong reddish colour. In images of modest resolution it covers everything from NEB to NNTB! In hi-res images it is located on the NEB and NTB and a segment of NNTB, but the zones between appear grey. This is clearly a sequel to the violent NTB outbreak. The SEB may well turn similarly red next year, after its revival is complete.

Best wishes,

John

Jupiter's Circulating Current, Part 3

Hello all,

Here you can see the progress of the SEB Revival and the Circulating Current, in the two attached sets of images.


The Circulating Current is spectacularly visible at STrD-1. The individual dark spots involved with it (transferring from SEBs to STBn) are presumably anticyclonic circulations themselves, as confirmed by their orientations during mergers. Spots d and e merged on July 3-4, on SEBs, before reaching the STrD; spots a and b merged around July 16, on STBn, after exiting from the STrD. Spots f and g and are circulating thru the STrD today.

At STrD-2, which appears to be much weakened by the SEB Revival source beside it, no circulation is visible. In fact, two dark spots prograded up to it in the STBn jet but have passed by it without interruption (apparently just a transient deflection and hesitation; yellow arrows in 'SEBO set').


The SEB is now filled with intricate turbulence both p. and f. the original source. The disturbance p. it has spread all the way to the Red Spot Hollow. F. the source, dark spots are still being created on the SEBs retrograding jetstream, providing many more opportunities to observe the Circulating Current in the coming weeks.

There is still little disturbance p. the RSH, where the SEB(S) has continued to fade until it is now almost invisible. Indeed the latest images show a blue streak Np. the GRS, which is typical of the faded state of the SEB.

Happy observing,

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

http://www.britastro.org/jupiter

Jupiter's Circulating Current, Part 2

Hi everyone,

These images complete the set showing the recirculation of the first two SEB(S) spots at the South Tropical Disturbance. Both spots (a and b) are now prograding in the STBn jet-stream at ~3 deg/day.

Congratulations to all the observers who have contributed to this, especially Isao Miyazaki, and all the European observers who took images on Friday night (July 6). You have obtained images on almost every rotation of the planet from July 6-9, and produced a perfect record of the Circulating Current!

Please keep on imaging, as there are two other very interesting phenomena still going on:


1) SEB(S) spots d and e merged on July 3, but has appeared elongated again. These two spots were very large and dark, and the merged one is even larger. Sometimes, a merged spot like this becomes a slow-moving anticyclonic ring in the STropZ, so I wonder whether this spot will proceed to STrD-1 like its predecessors, or whether it will produce a separate circulation that may interfere with that of STrD-1. The latest image shows spot a alongside it, and although the apparent connection may be due to limited resolution, it is worth watching.

2) On July 7 at STrD-2 (L2 = 175), Miyazaki's image showed two little dark spots prograding on the STBn jet-stream: the leading spot was in contact with STrD-2 (see attached image). Is this spot recirculating from STBn to SEBs, i.e. the converse of the Circulating Current seen at STrD-1? Recirculation in this direction has never been directly observed so this is also worth watching! Or (as STrD-2 appears much weakened by the SEB Revival) perhaps the spots will just drift past it.


Best wishes,

John Rogers

Jupiter: Circulating Current observed!

Interim report on developments on Jupiter: THE CIRCULATING CURRENT!

The first of the retrograding dark spots on the SEB(S) has indeed recirculated to the STBn jet at STrD-1, in the first display of the Circulating Current ever to be fully documented by imaging. The second spot is recirculating now!
These events started on July 1 as predicted, and have been followed almost single-handedly by Isao Miyazaki (Okinawa, Japan). This images would have greatly delighted the old BAA observers who were the first, and last, to record this phenomenon in the early 20th century.

The Circulating Current, at the p. side of a S. Tropical Disturbance (STrD), transfers spots from the SEBs jetstream (westward) to the STBn jetstream (eastward), causing them to reverse their drifts of around 4 deg/day or ~200 km/hr! This phenomenon was first recorded during the SEB Revival in 1920, and again in 1932-34, by BAA visual observers. Those observations involved the Great STrD, and were thoroughly described by B.M. Peek in his book. There was no further STrD with an observable circulation until 1979 when one fortunately arose during the Voyager 2 encounter, but the Voyager images showed that SEB(S) spots became trapped and destroyed in the circulation, rather than emerging onto the STBn. In 1980-81, spots did emerge p. the same STrD in the STBn jetstream, but it was not clear if they had recirculated from SEBs. In 1993, there was again a STrD during the SEB Revival and there was evidence for circulation within it but no further. Thus, the present observations are the first in the modern era to show complete recirculation from the SEBs jetstream to the STBn jetstream.

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The attached set of images shows the phenomenon in detail. (It also shows mergers of two pairs of spots which overtook each other: two mini-barges in the SEB, and two other dark spots in the SEB(S) chain.)

More images are urgently needed, on every rotation this weekend, to track the second spot (b on the attached images), and to check whether the first spot (a) is now stably in the STBn jetstream. STrD-1 is at L2 = 322.

THE S.E.B. REVIVAL OUTBREAK:

Finally, a quick summary of the progress of the SEB Revival:

The southern branch consists of the dark spots retrograding on SEB(S); there is now a long chain of them from the source up to STrD-1.

The source region, at L2 ~ 180, continues to produce bright and dark spots and is a scene of great turbulence. Recently STrD-2, next to the course, has darkened again.

Turbulent spots have now prograded to the Red Spot Hollow, and it was not clear whether they would extend p. it. On June 27, images revealed were two striking developments from this interaction: (i) a very dark rim developed on the f. side of the Red Spot Hollow (presumably prograding dark material reflected around the GRS); (ii) a long series of 'waves' on the SEB(N) p. the GRS (indicating that disturbance from the SEB Revival may now be extending p. the GRS).


The activity continues...

John Rogers

Here is a quick update as the New Horizons flyby on Feb.28 approaches. Some amateur observers have now been able to get enough good images that we can predict where the main features of interest at that time. Thanks to Fabio Carvalho (Brazil), Tiziano Olivetti (Thailand), Chris Go (Philippines), and Anthony Wesley (Australia), for these images. The following drift rates are approximate, as they are derived partly from my manual measurements on these images (which will be superceded when the JUPOS team have completed their work), and partly from measurements on the early New Horizons images which I fitted to an assumed track for SSTB-oval-A8.

EZ(S), SED, and SEB:

The EZ and SEB appear dramatic, with much shading and coloration. In the EZ, there is an intricate mixture of blue-grey festoons with the broad brownish EB that developed during 2006. The EZ(S) is very disturbed, largely due to the S. Equatorial Disturbance (SED).

The main complex of the SED is now (Feb.18-19) passing the GRS. It now appears as a great white spot, as in the Voyager era; this is a spectacular transformation of the feature that we have tracked since 1999. Apparently its appearance owes more to the surrounding cloud patterns than to its internal dynamics. There is much disturbance p. it, which looks like (and may be) a series of great waves; the most obvious is a second large white patch 30-40 deg. p. the main complex. The movement of the SED seems to be variable (as has been noted before when it is very active): its drift DL1 was ~+22 deg/mth from 2006 May to Dec., then >+30 deg/mth in mid-Jan., but only ~ +20 deg/mth now.

Following the SED is a prominent dark reddish sector of SEB(N). Elsewhere SEB(N) is quite narrow, and there is an extensive SEBZ: perhaps this will develop into general fading of the SEB later this year? (The SEB is internally still quiet.)

In contrast the SEB(S) is strikingly dark red. Perhaps this is part of the same coloration event that started with dull shading in the EZ in 2006 and has spread southward, intensifying over the SEB? The few 'mini-barges' within it have become very prominent, very dark red, in hi-res images. One is f. the GRS and one has just passed STrD-1.

STropZ and STB circulations:

STrD-1 and -2 persist as prominent features, both now prograding in L2 as expected. They were well shown in the early pairs of New Horizons images, but the circulations still could not be clearly resolved, apart from one pair of images which seemed to show the expected anticlockwise circulation at the f. edge of STrD-2. Hopefully the close encounter images will show STrD-1 much better.

STrD-1 split into separate p. and f. components, both with variable drift, and the f. one faded away as oval BA passed it, leaving just a faint outline behind on Feb.10-13. About the same time, oval BA seems to have accelerated. These changes may all have been connected. The p. edge of STrD-1 had also accelerated to DL2 = -8 (+/-2) deg/mth; it will be interesting if it and oval BA move as a coupled pair in future.

Below is a table of recent estimates of the drift rates of these features, and their projected positions on Feb.27. Also attached is a montage of 4 recent images showing the major features.

John Rogers
2007 Feb.18


Predicted positions on Feb.27
(from data to Feb. 17):

	DL2 (deg/mth)	L2	L3
GRS		116	334.5
Minibarge in SEB	+8.5	5	223.5
P. end STrD-1	-8	347	205.5
F. end STrD-1	(disapp.)
Oval BA	(var.)*	358	216.5
STrD-2	-3	218	76.5
	DL1 (deg/mth)	L1	L3
SED	+20	226	280

*Oval BA has recently accelerated from previous DL2 = -12.5 deg/mth

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The beautifully sharp rotation movie from New Horizons on Jan.8 confirms the major changes that had been reported from the first amateur images of the apparition: the termination of activity in the SEB, and the appearance of a new South Tropical Disturbance (STropD).

Attached is a montage of both NH and amateur images showing the major features of the new apparition. Thanks to Anthony Wesley (Australia), Fabio Carvalho (Brazil), Tiziano Olivetti (Thailand), and Chris Go (Philippines) for these images. The top row shows the striking colourful grouping of oval BA, the STropD, and the S. Equatorial Disturbance.

Reviewing the major changes from the equator southwards:

EZ(S) darkens, SED is more visible:
The yellowish shading which began to appear in EZ(S) last year (continuing the darkening of features all across the EZ in 2006) has continued, and EZ(S) is now mostly dusky brown. The dark NEBs projections and bright patches in EZ(N), along with other dark shadings in the EZ, now make a very striking picture.

The long-lived S. Equatorial Disturbance, tracked since 1999, appears to be still present (L1 ~ 185) and passing the STropD. In the top row of images (Jan.8-15), the main complex of the SED is identified by a bright patch, and the NH image shows this is a rift in SEBn with the classic SED structure. Immediately f. it is an amazing red shading! This must have developed from the brown shading seen there in 2006.

SEB activity has ceased:
The greatest change is the end of activity in the SEB. There are no white spots in the SEB f. the GRS, and no dark spots retrograding on the SEBs, and no dark rim round the GRS. Everything is quiet, for the first time for many years!

The last time all the activity stopped like this was in 1988. Then the SEB faded (whitened) in 1989 and the spectacular SEB Revival ocurred in 1990. So we may see the SEB fading some time in 2007, with the GRS becoming truly red. (It is already an isolated orange oval). This is the appearance that was imaged by the Pioneer spacecraft. This would be followed later by the spectacle of a SEB Revival (perhaps in 2008 or 2009).

This change seems to have started in mid-2006, as the two mid-SEB outbreaks ran their course. The retrograding spot activity on SEBs was coming to an end: only modest retrograding speeds were detected in 2006, and most of these ended in June. By Aug-Sep., although tiny spots and streaks still existed in SEB(SS) and STropZ, there were no coherent SEBs jetstream spots, and none were reaching the GRS. The GRS had already begun emerging as an oval separate from its surroundings from June onwards, and esp. in August. The sector p. the GRS was very quiet when last seen in 2006 Sep.

There is a new S.Tropical Disturbance (or two):
A STropD is a persistent dark structure spanning the STropZ, prograding in L2. Those observed at high resolution have shown recirculation of spots from the SEBs to the STBn at the p. edge of the STropD, and this is probably the dynamical feature that creates and defines it. They usually arise within some tens of degrees p. the GRS. One such was well observed by Voyager 2.
These images show a structure very like a STropD, just Np. oval BA, and the NH image shows the characteristic curving connections to the S. Tropical Band p. and f. it: I think we can call this STrD-1. Nor is it the only one. Wesley's image of Jan. 10 shows a second smaller example and this too has the characteristic structure in the NH image: let's call it STrD-2. Several important points arise:

1. Are they prograding as expected? This will become evident with more images.
   
2. Why are there two of them? I don't know, but the situation resembles 1993 the last time the SEB faded, and the last time a STropD was seen -- when there were two STropD structures before the SEB Revival. (The similarity wil be completed if white oval Q, probably still present in the NH imagery, becomes red like the GRS.)
3. Is STrD-1 connected to oval BA? Let's see if they move in parallel...
4. More specifically, did it originate as a consequence of BA's much-observed passage past the GRS last July?-- just as S. Tropical Disturbances and Dislocations (inc. the Voyager one) used to develop as the 3 old STB white ovals with adjacent STB white areas passed the GRS. No, it didn't. As oval BA reached the p. edge of the GRS in late July, there was considerable disturbance in the STropZ p. it, but then everything calmed down. The STropBand prograded and faded. This sector p. the GRS was quiet when last seen in 2006 Sep.

However, there was a strong tendency for eddying in the STropZ in 2006 June.

The JUPOS charts (just produced by Hans-Joerg Mettig et al.) show that as the SEBs retrograding activity came to an end, in June, at least four slowly retrograding dark spots at 22-23 deg.S halted, drifted south, and reversed their drift briefly, before disappearing. Although similar behaviour was also seen by a few spots in earlier apparitions, it seems to have been unusually widespread in 2006 June and it was recirculation such as this which formed the STropD in 1979. So I suspect the passage of BA past the GRS, together with a general tendency to eddying in the STropZ as the SEB activity declined, favoured recirculations and mergers of some of the tiny grey streaks in this region, until they accumulated (during solar conjunction) into the anticyclonic hemi-circulation that forms a STropD.

Red oval BA and the STB Remnant persist:
Oval BA is still orange and still has the internal ring in the NH images. The faint wisp called the STB Remnant, which marks the second region of disturbance in the STB, is now approaching the GRS. It will pass it in mid-summer, when the STB Remnant may darken. The NH image hints that there may be an anticyclonic hemi- circulation on its p. side, which just might be the beginning of a new generation of great white ovals.... let's wait and see!

The SSTB white ovals persist:
The NH images show a regular array of nine little AWOs at ~41 deg.S, eight of which we tracked last year. They are the long-lived ovals A1-A5; a new small A6 which developed f. them in 2006; and three more p. them, where we only recorded two (A8 and A0) last year.

With all these changes, this promises to be a very interesting apparition.

John Rogers

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