[1]
Jupiter
in 2007 - First Report
(report, 2007
Jan.21st)
Jupiter in 2007: first report
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:
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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.
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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.
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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:
i) Are they prograding as
expected? This will become evident
with more images.
ii) 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.)
iii) Is STrD-1 connected to oval
BA? Let's see if they move in
parallel...
iv)
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.
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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!
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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.
______________________________________
Jupiter
Section Director,
British
Astronomical Association.
jhr11@cam.ac.uk
http://www.britastro.org/jupiter
_______________________________________