2001/05/19: Formation of NEB Rift in 2000-2001
NEB Riftの生成過程
(Yuichi Iga)

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NEB Riftの生成過程

2000-2001年の観測シーズンにはNEB内に数多くのRift が見られた。そこで、CCD画像から作成した展開図と、画像から計測されたNEBの白斑とRiftの経度を用いて解析を行った。その結果、NEB中央に白斑が発生すると、それはシアーされた気流に乗って東西に伸びると同時に南北にも伸び、NEB内のRiftが形成される。Riftはその後の白斑の発生によって供給を受けて成長し、さらに東西に伸ばされる。15～30日間の成長期間の後、経度長が110°に達するとRiftは次第に消失する。白斑は同じ発生源から次々と発生して、新たなRiftを作り出す。この発生源は、シーズンで８ヶ所が同定されたが、平均自転周期は9時間54分15秒であった。また、発生源自身も３～５ヶ月の寿命を持っている。

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Formation of NEB Rift in 2000-2001

There were many rift structures on NEB in the apparition of 2000-2001. I generated 24 strip maps and measured the longitudes of white spots and rifts on NEB from CCD images. A small white spot occurs in the center of NEB, and it grows toward the east and west by the sheared jetstream and toward the north and south at the same time. Finally it grows to the rift of NEB. Because the rift is supplied from the new white spot, it is extended more toward the east and west. The rift grows up to 15-30 days, and disappears gradually after it has 110 degrees length of longitude. The white spots occur one after another in the same location of NEB, then its generate a new rift. These sources are identified to eight locations, and these have 9h54m15s of the averaged rotation period. Also, these sources themselves live until 3 to 5 months.

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Figure

Figure 1. CCD Images of typical aspects of the NEB in 2000-2001
Figure 2. Animation of NEB rifts
Figure 3. Strip maps of NEB region in 2000-2001 (1)
Figure 4. Strip maps of NEB region in 2000-2001 (2)
Figure 5. Strip maps of NEB region in 2000-2001 (3)
Figure 6. Model of the rift that is grown by the sheared jetstream
Figure 7. Drift chart of identified white spot and rift (plotted by special system=9h54m15s)
Figure 8. Model of the growth of the NEB rift