AURORA WATCH update

[Ulrich Rieth]

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This Is SKY & TELESCOPE's AstroAlert for Sun-Earth Interactions
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A s t r o A l e r t

Sun-Earth Alert

Solar Terrestrial Dispatch

http://www.spacew.com/astroalert.html

18 August 2002

CORONAL MASS EJECTION IMPACT ALERT - 18 AUGUST

"Better late than never" is the statement that many people use when
hunting down their favorite quarry - Aurora. A major solar flare observed on
16 August was associated with an Earth-directed coronal mass ejection that
was predicted to arrive at the Earth on 17 or early on 18 August. But nothing
happened at the predicted time, or even 12 hours later. Indeed, almost 24
hours elapsed before the elusive shock front was observed in the solar wind.
The ACE spacecraft, positioned about 1.5 million kilometers upstream of the
Earth, first detected the "blast wave" from the coronal mass ejection at
18:11 UTC. At that time, the solar wind suddenly jumped from background quiet
values near 410 km/sec to values near 580 km/sec. Impact with the Earth's
magnetosphere occurred near 18:58 UTC (2:58 pm EDT).

The late arrival of this disturbance will have a detrimental impact on
the ability the disturbance has to generate auroral storm activity ("northern
lights"). Auroral activity will not be visible from locations as far south as
originally predicted. Widespread middle latitude observations of activity are
still possible from dark-sky sites, but the activity won't attain the same
intensity that would have been observed had the disturbance arrived when
originally predicted. Low latitude regions (California to Texas to South
Carolina) will be hard-pressed and probably lucky to observe any activity at
all with this disturbance.

The middle latitude auroral activity watch has been updated with new
estimated visibility limits given the weaker state of this disturbance.

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MIDDLE LATITUDE AURORAL ACTIVITY WARNING

UPDATED: 18:35 UTC, 18 AUGUST 2002

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*** DISTURBANCE ARRIVAL ALERT ***

*** POTENTIAL FOR MODERATE TO HIGH ACTIVITY EXISTS ***

For North Americans, begin watching TONIGHT, the evening of 18 August.

VALID BEGINNING AT: EFFECTIVE IMMEDIATELY
VALID UNTIL: 19:00 UTC ON 19 AUGUST

HIGH RISK PERIOD: 18 AUGUST (UTC DAYS)
MODERATE RISK PERIOD: 18 - 19 AUGUST

PREDICTED ACTIVITY INDICES: 30, 20, 12, 12 (18 AUG - 21 AUG)

POTENTIAL MAGNITUDE OF MIDDLE LATITUDE AURORAL ACTIVITY: MODERATE TO HIGH

POTENTIAL DURATION OF THIS ACTIVITY: MAIN BELT = 6 TO 12 HOURS

MINOR BELT = 12 TO 24 HOURS

ESTIMATED OPTIMUM OBSERVING CONDITIONS: NEAR LOCAL MIDNIGHT

EXPECTED LUNAR INTERFERENCE: MODERATE PRIOR TO MOONSET BEFORE 1:30 TO 3:00 AM

OVERALL OPPORTUNITY FOR OBSERVATIONS FROM MIDDLE LATITUDES: FAIR

AURORAL ACTIVITY *MAY* BE OBSERVED APPROXIMATELY NORTH OF A LINE FROM...

(See Synopsis below)

OREGON TO SOUTHERN IDAHO TO EXTREME NORTHERN UTAH TO SOUTHERN WYOMING TO

NEBRASKA TO IOWA TO NORTHERN ILLINOIS TO INDIANA TO OHIO TO NORTHERN

VIRGINIA AND MARYLAD.

ACTIVITY *MAY* ALSO BE OBSERVED APPROXIMATELY NORTH OF A LINE FROM...

(See Synopsis below)

EXTREME NORTHERN FRANCE TO BELGIUM TO CENTRAL GERMANY TO CENTRAL POLAND TO

BELARUS TO CENTRAL RUSSIA.

SYNOPSIS...

The anticipated arrival of the coronal mass ejection associated with the
major solar flare of 16 August finally arrived at the ACE spacecraft 1.5
million kilometers upstream of the Earth at 18:11 UTC (2:11 pm EDT) on 18
August. This is almost 24 hours later than predictions suggested. As a
result, the disturbance will not be as strong as originally predicted.
Adjustments to the estimated limits of visibility have been included in this
mid-latitude aurora warning update. There is still a fair to good chance the
Earth will see periods of moderate to strong auroral storm activity over the
high and dark-sky middle latitude regions during the next 24 hours. Observers
are encouraged to keep a close eye on conditions now that the disturbance has
finally arrived.

This warning will remain in effect until 19:00 UTC on 19 August. It will
then be updated or allowed to expire.

PLEASE REPORT OBSERVATIONS OF AURORAL ACTIVITY TO:

http://www.spacew.com/submitsighting.html

CURRENT REPORTED SIGHTINGS OF ACTIVITY MAY BE FOUND AT:

http://www.spacew.com/www/auroras.html

** End of the AstroAlert Bulletin **
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[Bernhard Dorner]

Ist 'ne WARNING *o.T.*

[Heiko]

Leider reicht's wohl nicht bis in die Schweiz .... (( *o.T.*

[Thomas Saevert]

aber bis nach Holland *oT*