[18]  Circulating current report and images, August 13 - September 27; & Description of the planet, 2007 Aug.-Oct.  (2007 Dec.)

(1) The Circulating Current, Aug-Sep.

See montages posted below.

Recirculation and mergers of the jetstream spots continued.  On Aug.18, spots de and hi merged (forming di); over the next 2 days, spots L and pq also merged. Meanwhile another large spot was emerging from STrD-1, labelled R. (R is capitalised to indicate that I have note tracked its origin; it could also have resulted from merger of earlier spots, as all the previous spots did.)  On Aug.23, spots di and jk merged (dk).  By Aug.27-28 it appeared that spots ab and dk were merging, as were spots Lq and R; thus 16 of the 17 spots formed so far (except small spot c) had recirculated onto STBn and merged into just two complexes.  This process can also be followed on the JUPOS chart, which shows that the recirculated spots typically prograded at DL2 ~ -2.0 to -2.5 deg/day, but spots ab, de, and L all decelerated markedly, and this led to their apparent mergers with the spots following them in turn. 

However these last mergers (ab-dk and Lq-R) did not produce stable outcomes.  On Sep.1-4 they had broken up again into strings of small spots. One small very dark spot, resulting from the ab-dk merger, was almost stationary in the middle of the STropZ at L2 = 262 (Aug.30 – Sep.14). Some small dark spots were still prograding past it on STBn at ~-2 deg/day.  Subsequently, long gaps between good images make it impossible to track such features, but there were no large coherent spots on STBn. However STrD-1 remained as large and dark as ever, at least up to Sep.26.

On SEBs, the retrograding dark pots after L were crowded and difficult to follow. The JUPOS chart shows clear tracks which can continue the original numbering up to t, u, v, up to late August, but thereafter the SEBs spots were indistinct. Many of these spots were only modestly retrograding at first but accelerated in the retrograding direction to attain the full jet speed of about +4.0 deg/day.  (This was the exact speed of the first spot, and also the mean speed of these spots, +120 deg/mth; individual spots varied from this by  +/- 8 deg/mth, but there was no systematic change in speed as the Revival progressed.)

The September images show a densely spotty SEB(S) with a few distinct bright spots on SEBs.

(2) Description of the planet

This applies throughout 2007 September & up to mid-October, unless otherwise stated. Few images were recorded after September, and almost none after mid-October, even though the planet was still quite high in the evenings in the southern hemisphere!

See montages inc. [STrD1_Sept.,  SED_2007Sept.,  & Set-for-JBAA_2007Sept.]

STB:  Oval BA has a dark rim. The red colour in oval BA has faded, but is still present as of Sep.23 and Oct.29.

The STB is a broad dark belt p. and f. BA, in Sept. – presumably formed from dark material of the recirculated spots.  It has a tapered p. end, and a f. end continuous with STrD-1 in Sep.; then in Oct. it seems to be have detached from STrD-1.

STropZ: See above re Circulating Current.  STrD-1 remained prominent and dark into October, even though the recirculating activity was less conspicuous after Sep.1.  STrD-2 still existed too, thru Sep. & into Oct., still just a small hump and wisp. 

SEB(S) retrograding spots are smaller and less distinct in Sep., so cannot be clearly tracked thru the Circ. Current.

SEB: Double at all longitudes.  SEBZ is white p. GRS, shaded (turbulent) f. GRS.   F. GRS, in the source region of the Revival, there is still much disturbance but only small-scale.  P. GRS, the SEB(S) is dark right up to the RSH.

GRS has not faded; although the N half is paler than the rest, it is still a distinct dark orange oval.

So the anticipated fading of GRS and reddening of SEB have not yet occurred.

SED:  In August and early Sept. it had the classic appearance of a main complex with rift in SEB(N), preceded by a stormy sector.  It was passing STrD-1 in early Sept.  After that it appeared more irregular, tho the large white area at the main complex, with some dark blue-grey spots p. it, were still quite conspicuous. It passed the GRS on Aug.1, and again around Sep.25.  There were no good images of it after Sep.27.

EZ:  The exceptional dark grey-brown shading of the first half of the year, including the broad EB and festoons, were all fading, i.e the EZ was lighter again. This was already noted in July and the trend clearly continued in Aug. and Sept.

NTB: Strongly reddish after its revival -- orange-brown at all longitudes.

NTropZ, NTZ: Light, no strong colour.

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John Rogers

BAA Jupiter Section Director

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