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September 1999, Week 3


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Scott Mortimer <[log in to unmask]>
Reply To:
Vermont Skiing Discussion and Snow Reports <[log in to unmask]>
Mon, 20 Sep 1999 10:02:19 -0500
text/plain (44 lines)
     Sorry to take up so much bandwidth, but I thought would pass this on,
     given the recent conversation-
                Sun-Earth Alert            -------------------

     On 16 September, a large (~ 50 degrees heliographic extent) and dark
     solar filament (which is a prominence projected against the brighter
     background of the Sun's disk) erupted and produced a large coronal
     mass ejection. Later analysis revealed that although the majority of
     mass ejected by this event was directed well northwest of the Earth
     and out of the ecliptic plane, a small component appears to have been
     directed Earthward. The velocity of this disturbance is fairly low and
     will therefore require additional time to reach the Earth. But when it
     does, there is a chance it could produce moderate enhancements in
     auroral activity. The UTC day of 20 September looks to be the best
     period of time for enhanced auroral activity. The disturbance is
     projected to impact the Earth sometime late on 19 September or early
     on 20 September.

     This disturbance is not expected to be anything unusually spectacular,
     but has a better than usual chance of producing periods of strong
     auroral activity given the size and scale of the mass that was
     involved with this solar coronal mass ejection. So although most of
     the auroral activity is expected to remain confined to the higher
     latitudes and not be particularly significant, there is a notably
     slight chance activity could exceed expectations and become visible
     over more widespread middle latitude areas.

     The best times to observe activity will be near local midnight and
     the moon sets in the early morning hours.

     A full copy of the auroral activity watch has been included below for
     completeness. For more information and near-realtime images and data
     of auroral activity from the POLAR and TIROS satellites as well as
     from ground-based observations from amateurs world-wide, visit the web
     sites: and

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