SEB started fading from a sector preceding RS. Full scale of fading of SEB is the first time in 14 long years. It was expected that SEB would fade in the near future from previous examples, because post-GRS disturbance had halted during solar conjunction, and SEBs jetstream spots had also disappeared. Fading of SEB became noticeable in second half of April, when the south component lost contrast preceding RS, while the belt remained broad and dark following RS. Horikawa confirmed visually this situation on Apr. 25.

At the end of April, fading of SEB was limited to south component between RS and STrD-1. Though north component was still dark all round the planet, SEBs became faint as a whole, containing many barge-like small dark spots. Since previous examples of SEB fading also started from preceding RS, faded sector would expand eastward. But it had great variation in periods to complete the fadings: SEB faded rapidly in 1989, when entire of the belt almost disappeared within half a year, while it proceeded more slowly in case of 1991, in 1992 autumn one year after, SEBn was still dark and main part of the belt was recorded as dusky gray band. In addition, it is expected that SEB Fading will be followed by SEB Revival within a few years.

In northern hemisphere, dark broad NTB was developping by activities of NTBs jetstream outbreak begun in March. The leading spot (LS1), which emerged first, prograded almost half around the planet, and was at I:227.7 deg. (Apr. 29, Go). Its drift rate was -5.5 deg./day against System I, or rotation period was 9h46m50.8s (wind speed against System III was +168.8 m/s), which was a typical value as leading spot of NTBs outbreak. Following the spot, NTB was revived by disturbed sector containing irregular gray markings and tiny white spots. High resolution images showed that delicate features also expanded in adjacent zones. Another white spot (LS2) was observed immediately after the outbreak started, but it seems that it had disappeared by the mid-April. At the time of end of April, dark broad NTB revived between LS1 and around I:70 deg., followed by a sector of blue-gray spots extending to I:110 deg. On the other hand, NTB preceding LS1 was still faint and narrow, but tiny white spots and dark filaments were seen in high resolution images. In author's 16cm reflector, darkened NTB was a uniform belt in general, and no individual spot could be resolved. Because author was clearly able to see leading spot and dark spots in 1990 outbreak, it seems that this outbreak is comparatively moderate.

STrD-1 was gradually fading in accordance with SEBs becoming faint. Dark column at p. end was still obvious at II:335.6 deg. (Apr. 29, Fukui), and STBn was dark preceding it. While dark column was slowly prograding at -0.2 deg./day, f. end was stationary around II:10 deg., and whole length of STrD expanded to 35-40 deg. in longitude. On the other hand, STrD-2 was at II:199.6 deg. (Apr. 13, Miyazaki), and prograded at -0.4 deg./day, which was the same speed as LEBS. This month, slight step-down of SEBs appeared at about II:215 deg. It may indicate that f. end of the disturbance was forming.

Disturbed region in EZs (SED) passed through north of RS in mid-April. This region consisted of two large ovals and surrounding dark materials. The preceding oval was at I:269.2 deg., and the following one was at I:297.6 deg. (both Apr. 29, Yunoki). White rift of SEBn was connected to the preceding oval, where white cloud of SEBZ flowed into EZs. SEBn was remarkably dark following the rift.

RS was a strongly reddish oval having dark core at II:118.7 deg. (Apr.25, Kumamori). It was striking as surrounding zone was increasing brightness, though bluish STB remnant was passing through its south. It is expected to become much more prominent by SEB fading, because it is known that there is reverse correlation in density between RS and SEB. BA was a doughnut ring at II:330.1 deg. (Apr. 29, Ikemura), and it seemed that it became more reddish than before. NEB became narrower than before about half round the planet by retreat of its north edge to 17 deg. N in latitude. But NEB remained broad in two sectors, II:30-160 deg. and around II:300 deg., where n. edge was still about 20 deg. N in latitude. Only two portholes were left in north edge, one was WSZ at II:64.7 deg. (Apr. 18, Pujic), and the other was seen preceding it. Both were approaching to about 20 deg. in longitude, so it is expected that a merger of the two spots will take place as observed last apparition.

(2) Saturn

Saturn was at stationary on Apr. 20, and turned to prograding motion. Since it crosses the meridian soon after sunset, observation time is shifting to evening. This month, we have received observations listed below.

White spots were observed by Yunoki and Vandebergh this month too. On Apr. 5, Yunoki found some dark and white spots in SEBs-STrZ around III:320 deg. These were able to see only in emphasized image due to low contrast. Also, he detected a white spot in SEBZ at about III:240 deg. on Apr.12. Vandebergh created GIF animations which showed many delicate features. But no features were confirmed in images by other observers, because his images were too emphasized.

(May 15, K. Horikawa)

(Translated on October 4)

[Fig.1] SEB started fading preceding RS

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