Evolution of the anemone AR NOAA 10798 and the related geo-effective
flares and CMEs
Ayumi Asai(1,2,3),
Kazunari Shibata(4),
Takako T. Ishii(4),
Mitsuo Oka(4,5),
Ryuho Kataoka(6),
Ken'ichi Fujiki(7),
Nat Gopalswamy(8)
Abstract
We present a detailed examination of the features of the active region (AR)
NOAA 10798. This AR generated coronal mass ejections (CMEs) that
caused a large geomagnetic storm on 24 August 2005 with the minimum
Dst index of -216 nT. We examined the evolution of the AR and the features
on/near the solar surface and in the interplanetary space. The AR emerged
in the middle of a small coronal hole, and formed a sea anemone like
configuration. H-alpha filaments were formed in the AR, which have southward
axial field. Three M class flares were generated, and the first two that
occurred on 22 August 2005 were followed by Halo-type CMEs. The speeds of
the CMEs were fast, and recorded about 1200 and 2400 km/s, respectively.
The second CME was especially fast, and caught up and interacted with
the first (slower) CME during their travelings toward Earth. These acted
synergically to generate an interplanetary disturbance with strong
southward magnetic field of about -50 nT, which was followed by the large
geomagnetic storm.
(1) Nobeyama Solar Radio Observatory, National Astronomical
Observatory of Japan, Minamisaku, Japan
(2) National Astronomical Observatory of Japan, Mitaka, Japan
(3) Graduate University for Advanced Studies, Hayama, Japan
(4) Kwasan and Hida Observatories, Kyoto University, Yamashina, Japan
(5) Space Plasma and Aeronomic Research, University of Alabama in Huntsville,
Huntsville, Alabama, USA
(6) RIKEN, Wako, Japan
(7) Solar-Terrestrial Environment Laboratory, Nagoya University,
Nagoya, Japan
(8) NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
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