Dark spots on SEBs continued to make U-turns one after another by the Circulating Current at STrD-1, this month. But the evolution after U-turn was unexpected. At first, dark spots which moved to STBn from SEBs at STrD-1 were anticipated prograding rapidly with STBn jetstream. As expected, they began to prograde at around -3 deg./day after U-turn, but spot a and de decelerated soon. This was because they shifted to the north and strayed off from main flow of jetstream. For example, spot a was at -26 deg. in latitude immediately after U-turn, and it started deceleration as falling to -25 deg. after Jul. 10. In consequence of it, decelerated spots collided with following spots in succession, that is, spot a and b merged into spot ab, spot de merged with several spots from fg to jk (d-k in Fig.), and spot l merged with pr and r (l-r in Fig.). Spot ab continued deceleration and moving northward. It came to a halt in mid-STrZ at about II:250 deg. after Aug. 10, and at last, began to retrograde again. The last observation of spot ab was made on Aug. 25, when it located between spot d-k and SEBs as a diffuse spot in images by Hayashi and Takimoto.

There were 15 SEBs spots which reached STrD-1 by the end of August (while spots were retrograding along SEBs, d and e merged, and spot l also merged with some spots). Among them 12 spots began to prograde on STBn, because during U-turn, spot c disappeared and spot f and g, p and q merged. But due to mergers described above, only three spots remained. STrD-1 became dark and prominent, when large spots made U-turn.

By the way, new evolution seems to have started late August. Just after spot ab which made a U-turn again disappeared, spot d-k was stretched out to east-west direction, and developed a dusky shading connected with SEB (Go on Aug. 28, Miyazaki on Aug. 30). According to images taken early in September, this dusky area and prograding spot l-r merged to form a complex, from which an array of dark spots was formed on STBn. On the other hand, light rectangle area was left following the complex between STrD-1. Since within this area, latitude of SEBs edge was lower than outside, and no SEBs spots were seen, it seems that the complex acted as new obstacle, which blocked retrograding SEBs spots. Therefore, new STrD may have been formed in about II:260-270 deg. The further observations are required to confirm whether it is true or false. Please wait for next report.

Three months had already passed since SEB Revival took place. In a SEB sector between RS and source region of SEB Revival at around II:180 deg., irregular white spots were aligned in northern SEB, and SEBs was largely disturbed. STrD-2, located immediately south of source region, changed to a large bulge of SEBs, which consisted of tiny dark spots. Dark column in STrZ was hardly seen there. STrD-2 may be decaying. The source region of SEB Revival was still continuing supply of dark spots retrograding on SEBs, so U-turns of such spots at STrD-1 will be seen for a while in the future. On the other hand, SEB faded away preceding RS leaving SEBs as a weak streak. This is because SEBs dark spots did not retrograde beyond STrD-1, at which most of them made U-turns by the Circulating Current. But it seemed that dark material of SEB Revival was seeping through STrD-1, since narrow streak appeared along SEBs following STrD-1 after early July. This streak reached RS late August, when narrow outline of RS bay reappeared.

RS was a prominent oval with 17 deg. long at II:123.2 deg. (Aug. 29, Miyazaki). It was strongly reddish as ever without any sign of changes by SEB Revival. BA was at II:277.5 deg. (Aug. 23, Takimoto), but it became vague, since white collar surrounding reddish body disappeared. A large number of spots had been observed on STBn jetstream until last apparition. Though some spots were also tracked in this apparition, they were no longer seen hardly in August. EZ was still dusky too, and bluish festoons were seen not only in EZn but also in EZs. Disturbed region in EZs (SED) was not so conspicuous than before, but white rift breaking SEBn reappeared in August (I:46.9 deg., Aug. 14, Carvalho), so it may become active again. The whole region north of NEB was dusky and featureless with a reddish tint, and few spots were seen. Long-lived NEBn white spot WSZ which was temporarily indistinct due to NTBs outbreak was recovering brightness. But remarkable prograding motion observed before was lost, and it was stationary at about II:60 deg.

(September 6, K. Horikawa)

(Translated on February 27)

[Fig.1] The Circulating Current from second half of July to August

Return to OAA Top