[6] Jupiter in 2008: Full Interim Report. 2008 August.

John Rogers (British Astronomical Association)

 with data from the JUPOS project by Hans-Joerg Mettig & colleagues

Six weeks after opposition, with a new set of JUPOS charts just released, we can provide a fairly comprehensive report on the 2008 apparition so far, following on from our interim reports in May. A hi-res map of the planet in mid-July is Figure 1.

The JUPOS charts were produced by Hans-Joerg Mettig from measurements by Gianluigi Adamoli, Michel Jacquesson, Hans-Joerg Mettig, and Marco Vedovato: see

http://jupos.org so produces whole-planet maps every 7-10 days, which are placed on the ALPO-Japan web site:

http://alpo-j.asahikawa-med.ac.jp/Latest

Thanks are due to all the observers.  Australian observers have been hampered since July by winter weather and persistent bad seeing. Fortunately, Chris Go (Philippines) and Isao Miyazaki (Okinawa) have produced numerous hi-res images; several new first-class observers have joined the team in Australia and Brazil; and some observers in southern Europe, Japan, and the USA have managed to get decent images.  More good images have been provided via the ALPO-Japan web site and the (American) ALPO news-group, and we are very grateful to the organisers of these groups. 

 

SUMMARY:

Notable aspects of the major belts and zones:

Northern STropZ largely occupied by dark streaks and spots.

SEB still pale due to continuing turbulence in three sectors which now overlap.

Disappearance of most of the large NEBs projections and EZ festoons caused by:--

An unusually well-focussed and persistent bright rift in the NEB.

NEB still reddish-brown, but the north half becoming lighter.

NTB continuing to revive, with dark streaks developing in the wavy NTBn.

 

Highlights from hi-res analysis:

Rare detections of spots moving with or close to jetstream speeds in several latitudes.

Recirculation of prograding SSTBn jetstream spots at the STB Remnant.

Collision and eventual merger of the STropZ LRS with the GRS (described previously).

Confirmation of the velocity gradient of the SEBn jet preceding the S. Eq. Disturbance.

Discovery of a similar gradient in the NEBs jet, leading to the fastest speeds ever detected from Earth, in the absence of large NEBs projections.

Four mergers between barges in the NEB.

 

JUPOS detection of jetstreams:

We detect outbreaks of spots on five prograding jetstreams (S3TBn, SSTBn, STBn, NTBs, and NNTBs).  Retrograding jetstreams, as usual, do not display trackable spots with full jetstream speed, but we detect spots approaching those speeds on the STBs and NTBn – exceptionally rapidly retrograding for these latitudes – as well as SEBs.  In recent years JUPOS has often detected a pattern, in temperate domains, of small dark spots retrograding following larger slow-moving spots, and this is seen now in the S3TB, STB, and NNTB. 

 

NOTES:  In the following accounts:

Latitude bands refer to JUPOS charts.

All drifts (DL1, DL2) are in degrees longitude per 30 days, as usual.

AWO, anticyclonic white oval; LRS, little red spot (anticyclonic reddish oval). *See posted JUPOS charts.  (Black = dark spots, red = bright spots.)

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SOUTHERN HEMISPHERE

S. Polar Region (63-57oS):*

Three bright ovals are tracked here, two probably tracked since 2007.  The largest, near L2 ~ 60, has a pale reddish tint [Fig.2].  All three have variable speeds and the two smaller ones show regular oscillations with period ~42 days. 

S3Temp.R. (52-48oS):

One AWO persists (of the two present in 2007).  It had variable drift but now DL2 = -27.  Dark spots f. it move with DL2 = +17 to +27.

S3TBn jet (45-42oS):

The JUPOS chart shows definite activity with the full jet speed: at least four white spots (each lasting 2 months or more) and probably some dark spots, all with DL2 = -100!

S.S.Temp.R. (42-37oS):*

The domain is largely shaded, punctuated by 9 AWOs, all but one dating back several years, drifting steadily with DL2 = -25 to -28.  The sectors between the AWOs sometimes develop into white cyclonic circulations which always tend to grow longer, and in 2007 such white sectors existed between AWOs A1 and A2, and between A4 and A5.  The A1-A2 white strip grew until it was 30 deg long in 2008 June, then broke up.  The A4-A5 white strip has stabilised at a length of 40 deg.

A smaller cyclonic white oval existed f. AWO A6, separated from the AWO by a dark bar, and these broke up in July in an interesting manner [Fig.2].  The cyclonic white oval broke up suddenly in early July, just as it was passing oval BA which in turn was passing the GRS.  Such close passages of large ovals are known to destabilise adjacent cyclonic circulations (for instance, similar events led to mergers of AWOs in the STB and the SSTB in 2000 and 2001) . At the same time, the dark bar that separated the cyclonic oval from AWO A6 became brown; then the dark bar itself faded away, leaving reddish-brown haze which drifted p. to surround A6 (as pointed out in late July by Fernando P. Guimaraes). Now the colour is gradually thinning.  This seems to be another instance of a phenomenon that we have recently identified [see BAA 2001/02 report] – appearance of reddish haze over a dark cyclonic bar that is about to break up.

 

Fig.1 = Map of the planet, 2008 July16-19, made by Michel Jacquesson.

Fig.2 = Changes in SSTB f. AWO-A6.

 

SSTBn jet (37-34oS):

The chart shows a variety of prograding dark spots, including several with DL2 = -64 to -73, representing nearly the full speed of the SSTBn jet.  Two of these have recirculated at the STB Remnant (see below), and a third may be about to do so!

 

S. Temp.R. (34-30oS):*

The STB is still thin or absent around most of the circumference.

The STB Remnant is a long-lived, low-contrast, large cyclonic cell, ~20 deg. long, still very pale blue [Fig.3].  It is dark in methane-band images.  P. it is a much smaller oblique streak, also pale blue and methane-dark.  The surrounding STB has been absent (white and methane-bright), but in late July diffuse pale brown STB material prograded to this region, so in some images the STB Remnant now appears light with a slightly darker surround.

Its important status has been confirmed by the anticyclonic recirculation of two SSTBn jetstream spots, each of which performed a U-turn at its f. end, in June and in July [Fig.4] (and possibly one in early May which disappeared).  After the turn they retrograded in STZ, with DL2 = +8 to +12, for at least 2 weeks, though they then drifted south and ceased retrograding. 

Thus, the STB Remnant obstructs jetstream flow in the STZ.  In fact, Mettig recently posted a chart which suggests that similar recirculations have happened in other years starting in 2004: 

 http://jupos.privat.t-online.de/img/spec_STCS_1999-2008.GIF

This is interesting as we are looking for new large-scale anticyclonic circulations to develop in the STZ to replace the old AWOs which merged a few years ago.

Retrograding small dark spots are also seen elsewhere in the STZ, including one with DL2 = +36: probably the fastest yet observed here, close to the full speed of the STBs jetstream.

The most conspicuous S. Temperate features are still oval BA and structures f. it, with little change since last year.  Oval BA (DL2 = -14.5) still has a pale orange annulus.  There was little change in the oval or its surroundings as it passed the GRS: conjunction was on July 1 [see illustrations in previous report on the LRS].  F. it is the only really dark segment of STB, which breaks up to Sf. with retrograding spots (DL2 = +17), which terminate at a conspicuous, very dark oval in STZ (‘STZ Dark Spot’: DL2 = -16).  This must be anticyclonic so its very dark grey appearance is unusual; it resembles ‘DS3’ of a few years ago.

P. oval BA there is a long dark but narrow segment of STB(N) (see below); and diffuse light brown material is extending even further p. (see above).

 

STBn jet (30-26oS):

The STB(N) carries very small jetstream spots (DL2 = -99) that arise just p. the GRS, but are not distinct until they have passed another STB dark spot (L2=36 on July 9, DL2 = -16).  Some of them survive as far as the STB Remnant and a pair passed it with only temporary hesitation then re-acceleration.

 

Fig.3 = STB Remnant, 2008

Fig.4 = Recirculation of a SSTBn jetstream spot at the STB Remnant, 2008 July (with appearance of new white spots in the ongoing mid-SEB outbreak).

 

S.Trop.Zone (26-22oS):*

The GRS is at L2 = 124 --> 128.

Dark streaks and spots form a band in northern STropZ p. the GRS, with p. end(s) at L2 ~ 290-320.  Speeds are well-defined but diverse: the dark streaks have DL2 from ~-14 to +14, and smaller dark and bright spots in this band have DL2 = +30.  Similar streaks and spots with the same range of drifts have also come and gone at other longitudes, and are now (since June) becoming prominent f. the GRS as well.

The excitement of the collision between the Baby Red Spot (Oval 2) and the GRS has already been described.  Oval 2 had DL2 varying between -12 and -6; Oval 1, following it, has DL2 = -12, on course to arrive at the GRS in November. However, Oval 1 is now small and faint, and the dark streaks developing p. and f. it are more conspicuous. These streaks are prograding up to the f. end of the GRS.

The GRS interior is still orange with no obvious after-effects of the LRS collision, but it is now completely surrounded by a dark grey rim.  This seems to have developed from darkening of the previous S rim and extension to form a narrow N rim after the LRS passed round; extension of a dark stub at the p. end f. the LRS remnant; and accumulation of STropZ dark streaks into the triangle at the f. end.

 

SEBs jet (22-19oS):

The speed of the SEBs jet after last year’s STrDs is of interest, but it is barely detectable among all the other dark streaks.  Manual measurements have given DL2 ~ +78 to +90 for a few small spots over short intervals.  The JUPOS chart shows one dark spot with DL2 = +108 next to a white spot with DL2 = +76.  More detailed scrutiny may be worthwhile. ]

 

S.Eq.Belt (19-8oS):

Riding smoothly above the fray at ~17 deg.S is a series of four small dark spots (minibarges) with DL2 = +10.

The SEB is still very disturbed throughout, due to intense convective activity continuing in 3 sectors which now overlap:

1) The mid-SEB outbreak p. the GRS, which started at L2=100 on March 8. Still full of bright spots in May & June [Fig.5] and up to early August.  Sometimes rifts connected to the SED (see below).  The main f. end has prograded to L2 ~ 65 (July 5), 30 (July 26: another big bright white spot), 8 (Aug.22), but with further disturbance tapering Sf. for another 30 deg. or so.

2) The second mid-SEB outbreak, which started at L2 = 258 on March 21.  Still producing prominent white spots, e.g. new ones on July 14 (L2=248) and July 20 (L2=244) [Fig.4] (these went on to form a bright rift with the SED).

3) The perennial rifted region f. the GRS.

 

Fig.5 = Set showing NEB & SEB rifts, 2008 May-June

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EQUATORIAL REGION:

In the Equatorial Zone, all the exceptional darkness of 2006-2007 has disappeared, leaving only faint tenuous streaks, which however are complex and beautiful in hi-res images.  The south and north edges of the EZ have evolved to unusually similar states, with numerous tiny spots showing  very rapid speeds ahead of the few major features. 

SEBn jet (8-5oS):*

On the SEBn edge, the South Equatorial Disturbance is still an impressive feature (DL1 ~ +27 to +40), with a distinctive ‘stormy sector’ p. it.   [See Fig.6 & JUPOS chart, and also image sets in our previous reports on the LRS-GRS collision as the SED was passing the GRS in late June.  A more detailed report can be provided on request.]  Methane images show it as a methane-dark patch with SEBn ‘step-up’ as in previous years when it was active.

The main complex passed the GRS on April 29 and June 23 and August 17.  This year it has not been visibly rejuvenated when passing the GRS, but instead, its bright rift has been reinforced by connecting to rifts in the when mid-SEB outbreaks as it passes (June 4, July 9, July 16) [Fig.6].   These events reinforce my belief that the usual rejuvenations of the SED are not due to the GRS itself, but to the mid-SEB rifted region that usually follows it.  This year, the extensive mid-SEB outbreaks are performing that role instead.

The appearance of the main complex has ranged from the classic ‘active’ form with rift and great white spot (early May) to a remarkable cream-coloured large oval (late July) that contrasted with the innumerable small blue-grey streaks over the rest of the EZ. 

P. the main complex there has been an impressive ‘stormy sector’ of small but high-contrast spots and projections. The JUPOS chart beautifully confirms the pattern that we have reported since 1999: the chevrons move faster with increasing longitude p. the SED.  A preliminary estimate of speeds and distances is as follows:

                Deg. p. SED                        DL1                        u3                           Spacing

                                                                (deg/mth)               (m/s)

                0-50 deg.                          -27                          118                          8 -> 9 deg.

                ~120 deg.                        -56                           132                          irregular, 9-20 deg.

                >130 deg.                        -67                           137                          scattered

                ~280 deg.                        -73                           140                          one

These values are very similar to those recorded in 2000/01 during the Cassini flyby, when the SED was in a similar state of high activity.

 

NEBs jet (5-8oN):*

On the NEBs edge, the typical large projections have become subdued and few in number (DL1 ~ +4); most of them were destroyed in May-June by the prominent new NEB rift (see below), leaving just 3 consecutive large plateaux at L1 ~ 190-290 [Fig.6]. 

The space vacated by them is occupied by small spots and projections with unpreced-entedly fast speeds, which form a gradient p. the surviving large projections, just like the gradient of speeds on SEBn p. the SED.   Indeed in July the NEBs strikingly resembled the SEBn: there were only three reasonably large and persistent dark projections, forming a group with DL1 ~ +4 deg/mth, analogous to the SED; preceding them were small or moderate-sized dark projections with DL1 = -28 to -40 deg/mth, analogous to the stormy sector; and further p., more tenuous small projections and white spots with mean DL1 = -60 deg/mth.  [See Fig. 7, & the JUPOS charts. A more detailed report can be provided on request.]

Even the speeds of DL1 = -28 to -40 (in L1 ~ 100-180) are faster than almost anything reported in this latitude before 2001.  However, JUPOS analysis in several years since 2001 has recorded a similar class of small fast-moving projections and spots ranging from DL1 ~ -12 to -40 (mean ~ -23) (and one spot up to -56). (Speeds up to DL1 ~ -29 were also noted in the BAA reports in 1986-88.)  In those years, as now, the fast-moving spots were seen especially (though not exclusively) where the normal large NEBs projections had broken up, often due to passing rifts in the NEB. The present features are more notable because some of them have been quite conspicuous, but not for very long – so they may yet be a frequent phenomenon that was not clearly observable before modern techniques.

Even more novel are the faster speeds shown further p. (L1 ~ 300-20) by inconspicuous little oblique projections and white spots:  mean DL1 = -60 deg/mth, amounting to 134 m/s, which surpasses any previous measurements for the NEBs (except for one by HST). Around the whole circumference of the NEBs, the pattern of speeds forms a gradient very similar to that around the SEBn.  As it has only prevailed for one month, it is too early to make any definite interpretation: we will have to wait to see whether it is just a passing phase.

Meanwhile the bright reddish fringe of EZn is still visible at some longitudes (e.g. Aug.18, Haese); probably mainly in bright areas f. the few substantial projections, but not in the sectors with rapidly-moving spots.

 

Fig.6 = Set of maps in L1, 2008 May-August (prepared by Marco Vedovato), labelled to show the SED,  major NEBs plateaux, and new NEB rifts.

Fig.7 = Examples of very rapid spots on NEBs, 2008 July (excerpts from larger sets)

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NORTHERN HEMISPHERE

N.Eq.Belt (10-17oN) & N.Trop.Zone (17-21oN):*


The NEB is still strongly reddish, and still very dark in its south half; but from June to August, paler sectors (quiet NEBZ)  have formed in the north half around most of the circumference, leaving a narrow brown NEB(N) incorporating the dark barges.

An unusually stable NEB rift has existed since May [Figs.5 & 6]. It appeared on May 3 as a small white spot in southern NEB beside the p. end of a NEBs plateau, drifting close to System 1.  Within a week it matured into a still-compact but extremely bright white spot, with narrow extensions Sp. and Nf., and a steady drift of DL2 = -133, up to mid-June. Then it became a more extended rift, with faster drift again, until mid-July.

As this rift faded, a new similar feature erupted on July 22 – a very bright white spot adjacent to a conspicuous NEBs dark plateau, which had just been passed by the earlier rift.  It has evolved similarly (spectacularly bright on Aug.3:  Salway).  A third such white spot appeared on Aug. 11, and has become as brilliant as its predecessors [Fig.6].

In the NEB(N), there are now seven barges, following four mergers as listed in the previous report. The second of those is shown in [Fig.8].  The third and fourth happened as predicted, the fourth being the best observed (in late May at L2 ~ 270) [Fig.9].  The event was similar to previous ones that we have described [Rogers et al., 2006b, Icarus]: no prior acceleration, and the merged barge (longer than either parent) moved with a speed intermediate betweeen the two parents.  However the event did show more evidence of cyclonic vorticity than previous ones [Fig.9].

The NEB(N) still protrudes north around the barges and wiggles south around several bright white bays. One of these is white spot Z (WSZ): hi-res images show it encompasses a smaller, very bright white spot quite far north in the NTropZ (~21 deg.N?).  [E.g:  Wesley, May 9; Grassmann & Salway, July 16; Kazanas & Go, July 23; Go, Aug.9; Barnes, Aug.12; Salway, Aug.24.]

Fig.8 = NEBn/NTropZ: AWOs collision and barges merger, 2008 April.

Fig.9 = NEBn barges merger, 2008 May-June.

 

NTBs jet (22-25oN):

Earlier we noted several pale orange ‘lozenges’ within the dark orange NTB(S), moving with DL1 ~ -78.  The JUPOS chart shows that four of these have persisted from April to now, with average DL1 = -78 (range -74.5 to -81.5).  A cluster of shorter-lived ones, with DL1 ranging from ~70 to -82, disappeared in June.

N.Temp.Region (25-33oN):

Both components of the NTB have now revived, with pale reddish colour between them.  The NTB(S) is still dark and strongly orange, although the colour may be becoming slightly less pure (more brown). 

The NTB(N) has been reviving as a sinuous grey band, faint at the start of the year but quite strong now.  Its remarkable wavy pattern has become conspicuous as the belt darkened, and dark grey streaks or barges are now forming in some of the waves.  The pattern of waves is neither regular nor stable – spacings are ~10-20 deg. – but tracks are well defined all around the circumference, with DL2 = +21 to +31.  This is not as rapidly retrograding as the NTBn jet measured by spacecraft, but notably more so than the historical N.Temp. Current.

The extreme waviness in the NTBn latitude was actually present, at low contrast, in HST blue-light images on 2007 March 25 before the outbreak (Dr. Amy Simon).  It was also present in a 1979 Voyager close-up, but not in 1999 HST nor 2000 Cassini images. So it may be a correlate of the super-fast (NTC-D) state of the NTBs jet, and now it has been visualised by the revival of dark material in the NTB.  

No NTB revival has ever been observed at such high resolution before.  The orange colour, the sinuous N edge, and the formation of barges by eddying within the waves, all resemble the phenomena of the NEB, and may be a similar response to the vigorous outbreak within the previous year.

 

NNTBs jet (33-37oN):

A substantial outbreak on the NNTBs jetstream is in progress: at least 17 small dark spots have been tracked, with mean speed DL2 ~ -84, though many spots show small variations.  They seem to be originating around L2 ~ 20-30 (March-July) though no special feature can be seen there.  As on the STBn, this may be a region where instability develops gradually along a long stretch of the jet.

Some of the NTBn ‘waves’ project far north into the NTZ, and one NNTBs spot actually recirculated to NTBn on encountering one of them (L2 = 245, May 20-22), and then disappeared.  However I have not found any more such events: although the JUPOS chart implies that several NNTBs spots may have disappeared when they reached NTBn projections, all that I have examined were vanishingly small and did not recirculate. 

 

N.N.Temp.R. (37-42oN):

The NNTB exists only in several separate dark grey segments: in July they are at L2 ~ 0-60, L2 ~ 190-225, and a more northerly (retrograding) one at L2 ~ 150-190.

We have thoroughly tracked six AWOs in the NNTZ, plus the LRS which is the largest such oval. The colour of the LRS has been fairly constant from March to July: modestly reddish, i.e. redder than oval BA, and very slightly redder than its surroundings.  (It may appear slightly redder in the latest images, Aug.18.)

In June, the LRS merged with a small AWO f. it [Fig.10]. Images on June 8 & 10 probably showed the tiny AWO swinging around the N edge of the LRS, but it was barely resolved; then there were no hi-res images until June 16, when the LRS was again single and undisturbed.  It was near-stationary at L2=87 throughout.  The only lasting change was an increase in its size: it was 8 deg. long before the merger, and 10 deg. long immediately afterwards and up to the present.    

Although this merger was not observed well enough to draw any conclusions, it prompts some further thoughts on anticyclonic mergers in general, also exemplified by the STropZ LRS and GRS, and by pairs of AWOs in the NEBn in 2006 and 2008 (see previous reports, and Fig.8).  These events, in which one partner was smaller, did not show the characteristic behaviour that we have reported for the rarer mergers of two substantial-sized AWOs [Rogers et al., 2006b, Icarus].  The NEBn AWO mergers in particular were surprising in that the smaller partner actually swung round the larger one, shrinking further as it did so, and was not visibly drawn into it.  This is exactly how the LRS-GRS merger would have appeared if reduced to the same scale. In fact, the visible LRS remnant was just one part of the original oval, stretched into a narrow ‘lasso’ around the larger oval, and although it became inconspicuous, it actually survived and was drawn back into the larger oval. 

 

Fig.10 = NNTemp. LRS merging with a smaller AWO.

N3, N4, & N. Polar Region (42-56oN):

Many white spots are tracked on the JUPOS charts at various latitudes in this range, with typical N3TC and N4TC drifts.  The most well-defined is near 50 deg.N with DL2 = +8 (N4TC).

2008 August 24

______________________________________

John H. Rogers, Ph.D.

Jupiter Section Director,

British Astronomical Association.

_______________________________________