From: LARRY KLAES (firstname.lastname@example.org)
Date: Mon Apr 22 2002 - 17:51:51 PDT
----- Original Message -----
From: Cary Oler
Sent: Monday, April 22, 2002 11:09 AM
Subject: AstroAlert: Significant Solar Coronal Mass Ejection Alert - 21 April
This Is SKY & TELESCOPE's AstroAlert for Sun-Earth Interactions
A s t r o A l e r t
Solar Terrestrial Dispatch
21 April 2002
Details at: http://www.spacew.com/astroalert.html
SIGNIFICANT SOLAR CORONAL MASS EJECTION DIRECTED EARTHWARD
(PLEASE NOTE: This disturbance is projected to impact the Earth relatively
soon. This notice might not be delivered to all subscribers of AstroAlert
before the disturbance impacts. We apologize if this occurs. A private
distribution list has been established for those who require rapid delivery
of watch/warning material. Refer to: http://www.spacew.com/www/sublists.html
for details. This anticipated activity is being followed closely on the
aurora discussion forum at: http://www.spacew.com/aurora/forum.html for those
who are interested in near real-time information regarding the activity.)
As active sunspot complex 9906 was preparing to depart the west limb of
the Sun on 21 April, a large and significant class X1.5 solar x-ray flare was
observed. This event produced a prompt space radiation storm as energetic
protons travelling at near relativistic velocities began arriving at the
Earth about 5 minutes after the solar flare commenced.
A high velocity coronal mass ejection was observed emanating from the
west limb of the Sun. Peak plane-of-sky velocity measurements made by the
SOHO spacecraft science team suggest the velocity of the coronal mass
ejection may have been travelling near 2,427 km/sec - a very substantial
velocity. Although this coronal mass ejection contained an Earthward directed
component, most of the mass from the partial halo CME was directed well west
of the Earth.
The earthward-directed portion of the coronal mass ejection is expected
to impact the Earth sometime during the mid-to-late UTC hours of 22 April
(this translates to around noon or the afternoon hours in Europe and the
early to mid morning hours near dawn for North America). This places
Australian/New Zealand and European sectors in the best positions for
observing potentially strong auroral storm activity after the coronal mass
ejection impacts the Earth's magnetosphere. Whether activity holds out long
enough for North American observers to spot activity is an open question.
However, North American observers should be aware that an earlier than
expected impact (which is possible, but less likely) prior to 12:00 UTC may
provide them with a predawn light-show for a few hours.
Observers across the world and even into the lower latitude regions are
encouraged to watch the skies on 22 and 23 April for possible auroral
activity ("northern lights").
A middle latitude auroral activity warning has been issued for this
event, details of which have been appended below.
MIDDLE LATITUDE AURORAL ACTIVITY WARNING
ISSUED: 20:41 UTC, 21 APRIL 2002
*** POTENTIAL FOR MODERATE TO HIGH ACTIVITY EXISTS ***
VALID BEGINNING AT: 06:00 UTC ON 22 APRIL (11:00 pm EDT on 21 April)
VALID UNTIL: 19:00 UTC ON 23 APRIL
HIGH RISK PERIOD: 22 - 23 APRIL (UTC DAYS)
MODERATE RISK PERIOD: 22 - 23 APRIL
PREDICTED ACTIVITY INDICES: 70, 40, 12, 10 (22 APRIL - 25 APRIL)
POTENTIAL MAGNITUDE OF MIDDLE LATITUDE AURORAL ACTIVITY: MODERATE TO HIGH
POTENTIAL DURATION OF THIS ACTIVITY: MAIN BELT = 12 TO 18 HOURS
MINOR BELT = 18 TO 24 HOURS
ESTIMATED OPTIMUM OBSERVING CONDITIONS: NEAR LOCAL MIDNIGHT
EXPECTED LUNAR INTERFERENCE: MODERATE
OVERALL OPPORTUNITY FOR OBSERVATIONS FROM MIDDLE LATITUDES: FAIR TO GOOD
AURORAL ACTIVITY *MAY* BE OBSERVED APPROXIMATELY NORTH OF A LINE FROM...
OREGON TO NORTHERN UTAH TO NORTHERN COLORADO TO SOUTHERN NEBRASKA TO
NORTHERN MISSOURI TO ILLINOIS TO INDIANA AND EXTREME NORTHERN KENTUCKY TO
ACTIVITY *MAY* ALSO BE OBSERVED APPROXIMATELY NORTH OF A LINE FROM...
FRANCE TO SWITZERLAND TO SOUTHERN GERMANY TO NORTHERN AUSTRIA TO NORTHERN
SLOVAKIA TO SOUTHERN POLAND TO NORTHERN UKRAINE TO CENTRAL RUSSIA. NEW
ZEALAND AND SOUTHERN REGIONS OF AUSTRALIA ARE ALSO GOOD CANDIDATES FOR
AURORAL ACTIVITY SIGHTINGS.
A very intense, complex and high velocity solar coronal mass ejection
was observed early on 21 April. This disturbance had an estimated plane of
sky velocity of 2427 km/sec averaged out to 28 solar radii. Impact is
expected between 09:00 UTC on 22 April and 03:00 UTC on 23 April, with a
preferred impact time of near 12:00 to 15:00 UTC (give or take several hours)
on 22 April.
This is a potentially significant disturbance that could drive periods
of intense auroral storm activity. Middle and low latitude regions may be
able to spot periods of significant activity after this disturbance impacts.
At least a portion of the CME was directed Earthward, although the bulk of
the highest velocity material was directed well west of the Earth.
Note that our projected activity index for 22 April (listed as 70) may
be on the conservative side.
This warning will remain in effect until 19:00 UTC on 20 April. It will
then be updated or allowed to expire.
PLEASE REPORT OBSERVATIONS OF AURORAL ACTIVITY TO:
o A new and advanced space weather, auroral activity, and terrestrial weather
monitoring tool is available at: http://www.spacew.com/swim
o Real-time notification of events via Digital SMS (cell phone/pager):
using the SWIM software.
o Monitor real-time conditions and report sightings using software at:
o On-line global discussion forum:
o Chat in real-time with others using IRC at:
and join the #aurora channel (type /join #aurora in the IRC software).
** End of the AstroAlert Bulletin **
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