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Дата изменения: Sun Mar 7 14:39:53 2004
Дата индексирования: Sun Apr 10 01:19:24 2016
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The Basille Day 2000 Event
We have analyzed dimmings (i.e. transient coronal holes) and manifestations of a
coronal wave in the famous event of 14 July 2000 using images produced with the EUV
telescope SOHO/EIT. Our analysis was inspired by a paper of Andrews (2001), in which
this event was studied using running-difference EIT images at 195 Å formed by the
subtraction of a previous image from each current. Running-difference images
emphasize changes of the brightness, location, and configuration of observed
structures occurred during the 12-min interval between two subsequent heliograms.
However, they distort the picture of large-scale disturbances caused by a CME,
particularly, dimmings. A real picture of dimmings can be obtained when derotated
fixed-difference images are considered. The latter are formed in two stages: first,
the solar rotation is compensated using three-dimensional rotation of all images
(`derotation') to the time of a pre-event heliogram, here 10:00 UT, and then
the base heliogram is subtracted from all others. We show real dimmings to be
essentially different from those described by Andrews (2001). The reconstruction of
large-scale magnetic fields in the corona in connection with the CME is accompanied by
the appearance and growth of two large dimmings. One of them is located along the
central meridian, southward of the eruptive center, at the place of the pre-eruptive
arcade. Another dimming occupies the space between the flare region and a remote
western active region. Moreover, fragmented dimmings are observed virtually overall on
the solar disk, especially, within the northwest quadrant. A propagating disturbance
with properties of a coronal wave has been also revealed in the north polar sector.
We also suppress the `snowstorm' produced in the images by energetic particles
that allows us to consider the dimming manifestations in all four EIT passbands
171, 195, 284, and 304 Å, as well as the light curves of the main dimmings including
several later images at 195 Å.
 

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