--------------------------------------------------------------------- JUPITER IN 1994: SECOND INTERIM REPORT by John Rogers for BAA This report on jovian cloud appearances before the comet crash has been sent out to the IJW people by Glenn Orton. Summary follows: In view of the imminent comet impacts, this report concentrates on the high southern latitudes. Large-scale disturbances continue in the S.S. Temperate region, notably five large, very dark patches associated with five small white ovals at 41 deg.S. The S. Temperate Belt shows internal rifting and STBn jetstream spot activity preceding oval BC. The S. Tropical Zone is still narrowed by a dusky band in its northern half. The Great Red Spot has lost its very dark rim but is still reddish. The S. Equatorial Belt still has reddish colour in its south half and spots in its north half, as the Revival reaches its conclusion. The very bright Equatorial Zone and the very broad N. Equatorial Belt seem to have started returning towards a more normal state. John Rogers, July 9. --------------------------------------------------------------------------- JUPITER IN 1994 SECOND INTERIM REPORT John H. Rogers British Astronomical Association [JR@mole.bio.cam.ac.uk] *********** 1994 July 5 *********** SUMMARY In view of the imminent comet impacts, this report concentrates on the high southern latitudes. Large-scale disturbances continue in the S.S. Temperate region, notably five large, very dark patches associated with five small white ovals at 41 deg.S. The S. Temperate Belt shows internal rifting and STBn jetstream spot activity preceding oval BC. The S. Tropical Zone is still narrowed by a dusky band in its northern half. The Great Red Spot has lost its very dark rim but is still reddish. The S. Equatorial Belt still has reddish colour in its south half and spots in its north half, as the Revival reaches its conclusion. The very bright Equatorial Zone and the very broad N. Equatorial Belt seem to have started returning towards a more normal state. OBSERVATIONS This report covers 1994 May and June, following on from our first interim report dated May 9. It also includes higher-resolution notes on earlier aspects, from Don Parker's superb CCD images. Data are principally from the following observers. Don Parker (Florida), hi-res CCD images with colour filters, to April 17. Isao Miyazaki (Okinawa), hi-res photos, to May 20. Richard Schmude (Texas), colour photos, to June 6. Franco Balella (Italy), visual transits, to June 25. Mike Foulkes, David Gray, John Rogers (England); Mark Bosselaers (Belgium); Hans Eggendinger, Andre Nikolai (Germany); visual transits and drawings, to June 30. CONVENTIONS (as in our previous reports): The standard names are used for belts and zones. P.= preceding (east), f.= following (west). This report uses System II longitude (\2) (see Table at end). All latitudes are zenographic, measured from photos or CCD images. WO = white oval. S. POLAR REGION Latitudes S of 43 deg.S are, as usual, almost featureless apart from some narrow belt segments (one centred at 58 deg.S). There have been two small light ovals (\2=174, 52 deg.S; \2=189, 62 deg.S; Parker images in March), and a short dark streak of SSSTB (\2 = 163-180, 46-51 deg.S; Miyazaki images in May). All were slow-moving in System II (in contrast to the rapid S.S.Temp. Current) but could not be accurately tracked. S.S. TEMPERATE REGION Latitudes 37-43 deg.S are still marked by unusually conspicuous structures. Bright strips ('SSTBZ') still persist, as in our previous report (erratum: cyclonic latitudes are 37-40 deg.S). Five major dark patches are associated with five tiny white ovals at 40-42 deg.S. These ovals are anticyclonic and have mostly been tracked since the late 1980s. The dark material is more variable. In detail (see Table at end for longitudes): (1) Dark patch p. WO, not conspicuous until May. This is at p. end of a bright SSTBZ strip, about 40 deg. long, which is followed by dusky patches. (2) Dark patch f. WO; one of the darkest, tracked with the WO since first obs'ns in March. (3) Dark material variable as WO moved p. oval BC; alongside disturbed STB sector in May. (4) This WO marks p. end of the main, long-lived, bright SSTBZ strip. It was overtaking ovals BC and DE in March-May. The big dark patch p. it developed then, and became very dark in mid-May as it merged with STB p. BC. (5) Very dark patch, p. WO, marks f. end of the main SSTBZ strip, and has been tracked since Jan. when it was conspicuous as it passed the GRS. The formation of this dark mass was observed in detail in 1993 (see our third interim report); then it seemed to be just a curiosity, but now it appears as a prototype for all five complexes. (6?) A very tiny WO has been recorded 20 deg. f. (5), and is embedded in a vague shading - a poor relation of the other five complexes. S.S. TEMPERATE REGION The STB is a major dark belt, grey in colour, but there have been interesting changes in three sectors within it. We describe these with reference to the white ovals in the belt (33 deg.S; see table at end for longitudes). The major disturbed sector lies between the GRS and oval BC. There is a separate narrow STB(N) component along here at 28.5 deg.S, which was prominent as early as the Spencer 5-micron image of Jan.6. As the resolution of photos improved from March onwards, tiny dark spots became evident on this STB(N), prograding at about -2 deg/day in \2. These are STBn jetstream spots. They appear about 20 deg. p. oval BC. At this longitude, Parker's images of March 20 showed a newly-appeared irregular light spot in the main STB that looked like a cyclonic filamentary region. This light spot may be the same as oval (a) which defined the f. end of the disturbed sector in May, with a bright streak in the STB p. it. Altogether these structures are suggestive of a region of cyclonic turbulence 20-50 deg. p. BC, generating dark spots on the STBn jetstream. Adjacent patches in the S.S.Temp. region contribute to the very disturbed appearance. Ovals BC and DE are still close together; their separation declined steadily from 21 deg. in Jan. to 14 deg. in May, but has now increased again to 18 deg. Midway between ovals DE and FA is a 20-deg-long oblong within the STB which has shown striking colour changes. Presumably it is a cyclonic circulation. Its p. end is always marked by the tiny white oval (b) (see table). On Feb.24-Mar.8 (Parker's images), the oblong was a notably dark 'barge' with reddish-brown colour - a rarity for this latitude, contrasting with the grey belt around it. But from April 2-16 (Parker's and Miyazaki's images), it became a bright streak, yellowish in colour. Then it turned dark again, merging into the STB (Schmude's photos later in April and Miyazaki's in May). The third disturbed sector of STB, in May, is alongside the GRS, where the belt is broken into spots. Again, patches in the S.S.Temp. region contribute to the very disturbed appearance. S. TROPICAL REGION The STropZ is still narrowed by the dusky Band in its N half (23 deg.S), which is detectable at most longitudes. Although the S half is quite bright at many longitudes, many photos and drawings confirm the presence of indistinct shadings and white areas, many of them ephemeral but some moving with \\2 = -7 deg/mth. The shadings often seem to be continuous with the faint Band. However, the well-structured S. Tropical Disturbance of 1993 is no longer distinguishable. The most conspicuous features are the brilliant white oval fixed at \2=302, and the dark segment of the Band extending for 20-30 degrees p. the GRS. The later segment seems to have faded lately as the GRS lost its very dark rim. The GRS is still reddish but now seems to float free of the SEB [visual obs'ns since mid-May]. *****If anyone has any hi-res images before mid-February, around \2 300-360 or \2 100, I would be very grateful for copies, in order to determine what happened to the STropD and where the bright WO came from.******** The main part of the SEB is orange-brown. [Confirmed by Parker and Schmude images; in Parker's images, this tawny colour is more evident from March 10 onwards.] This is the 'orange flush' that usually follows a SEB Revival. It contrasts with the bluish-grey band in the STropZ, and with the narrow, dark grey SEB(N) component. There are still many small spots in the N half of the SEB. SEB(N) is interrupted by several gaps or white ovals. Parker's images show that they often have a bright orange border on the Sp. side, and a very dark, bluish segment of SEB(N) on the f. side. They are moving at \\2 = -200 deg/mth; thus SEB(N) activity appears to be gradually accelerating towards System I, which is also typical after a Revival. EQUATORIAL REGION Although the EZ sometimes appears bright white as it did earlier, at other longitudes a more normal filigree of light grey or bluish wisps and shadings is apparent. There have also been some brilliant white spots on the equator. We have not yet analysed the features in detail, but have the impression that large dark bluish-grey patches on NEBs are more common or conspicuous in recent months. N. TROPICAL REGION Early in the year, the NEB was very broad (N edge at 20 deg.N), and free of bright 'rifts'. As in 1988, rift activity was suppressed for several months after the broadening event. Now, some major bright rifts have appeared again. Two new, very dark brown 'barges' have formed at 16 deg.N within the NEB. Along with the small dark spots and bright oval previously recorded, perhaps these could be the start of the predicted global array of spots? One barge at \2=325 was first recorded on April 17, and moves at \\2 = -5 deg/mth. The other at \2=192 was first recorded as conspicuous on June 6. (However it was visible as a small dark spot in Miyazaki's photos as early as May 8-10, adjacent to a newly-erupting rift; this was one of several tiny dark spots that appeared from then on alongside this rift as it prograded in the NEB. Earlier, there were small dark spots at the same latitude at \2 36, 56, 106, but these have not been recorded since late April when rifts began to pass them.) The NEB is brown as usual, and the dark barges in it are the same colour. The 'warm brown' N half is offset by the S half which consists largely of dark 'cold grey' patches or streaks with some big dark blue projections. Some of Parker's images also show the extreme NEBn edge as cold grey. Meanwhile the NEBn edge may be starting to recede at some longitudes. Several visual observers have this impression, and in one sector (approx \2 80-230, May onwards) it is clear that a light strip has formed in the northern extension of the belt leaving a tenuous NEB(N) at 19 deg.N. The NTropZ remains narrow and shaded and patchy, with NTBs jetstream spots protruding into it. TABLE OF LONGITUDES AND DRIFTS ---------------------------------------------------------- Current/Features \2(O) \2(C) \\2 ---------------------------------------------------------- S.S.S.Temp.Current Short dark bar (49 deg.S): 172 188 (+6) S.S.Temp.Current Small white ovals (41 deg.S) with v. dark patches p. or f: DS(1) (0) 301 (-22) WO(1) 5 306 -22 WO(2) 93 23 -26 DS(2) 103 33 -26 DS(3) (138) 72 (-25) WO(3) 147 81 -25 DS(4) (179) 112 (-25) WO(4) 192 125 -25 DS(5) 297 227 -26 WO(5) 307 237 -26 S.Temp.Current White ovals in STB (33 deg.S): (a) 148 114 (-13) (BC) 184 152 -12 (DE) 202 170 -12 (b) 221 188 -12.5 (FA) 269 231 -14.5 S.Trop.Current Ovals (22.5 deg.S): GRS 42 42 0 WO 302 302 0 N.Trop.Current Dark barge (16 deg.N) 322 309 -5 Bright WO (19 deg.N) 80 73 -7 before opp., -3 since opp. ---------------------------------------------------------------------------- \2(O) is System II longitude at opposition on April 30; \2(C), extrapolated to July 19. Speeds (\\2) are in degrees per 30 days (in brackets if imprecise). \3 = \2 + 50, on April 30; \3 = \2 + 71, on July 19; \\3 = \\2 + 8.0 deg/mth. All latitudes are zenographic. WO = white oval.; DS = dark patch. If this table is garbled by e-mail, send my your address and I'll mail it. ----------------------------------------------------------------------------