This month, a change of RS and its vicinity was noticed. SEBs edge had been active through this apparition, with large projections and dark rings preceding RS. It is conjectured that these originated from SEBs jetstream, but there were very slow-moving objects, gradually retrograding or almost stationary relative to System II. As described in last report, there had been three dark rings preceding RS in April, and two of them which had slowly been retrograding collided with RS in succession in May. Fig. 1 shows the second collision, in which dark ring traveled anticlockwise direction along n. edge of RS Hollow, similar to former examples. The drift rate of this ring was about +1 deg./day, much slower than typical jetstream spot. This may be because the ring much projected from SEBs edge was somewhat off from main flow of the jetstream, having higher latitude than other jetstream spots. On the other hand, there was an almost stationary dark ring at about II:60 deg. It was typical dark ring but one size larger than other retrograding rings, spanning more than half width of STrZ. Other retrograding rings passed through just north of larger ring toward RS, without showing any interactions. RS was distinct and reddish, and bridge connecting both edge with SEB was formed mid-late February. This would be an effect of collision with dark rings described above. Its longitude was II:102.4 deg. (Feb. 15, Miyazaki), continuing slight retrograding motion.

BA was prominent at II:353.6 deg. (Feb. 20, measured from Einaga's image) with dusky surroundings, and STB dark segment extended from BA to near RS. In other longitudes, only tenuous north component was seen, though it was darker preceding BA. SSTB was dark broad belt between II:240 deg. and BA, being double in Miyazaki's image, while it was faint and indistinct between BA and RS, where STB dark segment was present. In this sector, there were five long-lived white spots, but low-contrast against faint main belt made them difficult to distinguish in poor condition. Following RS, SSTB was narrow and located somewhat southerly. In STZ, two isolated tiny spots were seen around II:230 deg.

The post-GRS disturbance, the SEB area showing white clouds activity following RS, extended up to about II:140 deg., but not violent. Following this region, SEB was relatively faint and double by indistinct light band, and dark SEB started from II:200 deg. EZ was generally light with yellowish color in northern half, and EB lying as boundary was weak and fragmentary. Most of festoons were bluish and filamentary, fewer conspicuous ones than in last apparition, and bluish plateaus on NEBs edge were also fewer.

NEB rifted regions were seen in some places, but not so violent. Though bright rift sometimes emerged, it declined soon. In early-mid February, long rift developed and its p. end reached north of RS around Feb. 13, but it seemed to break up and disappear after then. Northern part of broadened NEB included an array of barges and white spots, and the belt was a little narrower being shaven off its n. edge, in a sector between II:210 and 300 deg., where barges and white spots were hardly seen. NTB was still absent in all longitude, and any sign of North Temperate Current-C was not seen.

(2) Saturn

Saturn was retrograding in Gemini, still in good period for observation. This month, we have received observations listed below.

White spots on Saturn were observed this month, too. Takimoto's image taken on Feb. 4 showed white spot in SEBZ accompanied by irregular shading around III:20 deg. Similar features could be seen in Pellier's image taken Feb. 6. Considering these longitudes, it seemed that these were the same feature or a series of markings of single phenomenon. Also, Yunoki observed a white spot in EZs around I:130 deg. on Feb. 8 and again Feb. 11.

It was noted in southern high latitude that outstanding reddening was observed in SSTZ surrounding SPR. This region had been characteristic blue-green tint before the apparition, showing beautiful contrast against other areas with warm color. Though redness in SSTZ was first noticed in January, it seemed to have already begun in early stage of the apparition, as a slight redness of the region could be seen in Grafton's image taken in October. In Pellier's images taken at several wavelengths on Feb. 27, SSTZ was bright in red and infrared showing SPR smaller, while it was as dark as bluish SPR in blue and ultraviolet in which SPR looks larger.

On the opposition effect of Saturn's ring reported by Yunoki last month, Einaga examined his images after 1999 for luminosities of ring and body around opposition against those 1-3 months before or after it, and pointed out that increasing brightness of ring similar to that observed this apparition could be confirmed. In his montage which included distribution chart of luminosity, ring B was obviously brighter than Saturn's body at opposition, while it was almost the same as or somewhat darker than that at other times. It presented that this phenomenon was not particular to this apparition.

(March 12, K. Horikawa)

[Fig.1] Collision of SEBs dark ring with RS

Ring (a) is being swallowed up by RS.

On the other hand, another ring (b) is approaching RS passing through just north of larger ring (triangle) which is almost stationary.

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