Astro Alert von Cary Oler

[Peter Wloch]

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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

18 November 2003

THEY'RE BAAACK!

Power-house sunspot Regions 10486 (currently the record-holder for
producing the largest solar x-ray flare in recorded history) and 10488
(another X-class producing spot complex) are returning to the eastern solar
limb.

Later today (and possibly tommorrow as well), these regions will be
renumbered. For now, we will refer to their old designations: 10486 and 10488
(or simply, 486 and 488).

Region 488 (which led Region 486 by roughly one day) has appeared as a
very large sunspot complex with a large penumbral mass. Size often matters
when dealing with large solar flares. Region 486 is not yet visible, but a
large solar flare behind the limb of the Sun where Region 486 should be, was
observed a few hours ago. An impressive loop prominence system (LPS) was
observed in h-alpha from this location. Major solar flare activity is now
considered possible given the strength of this current limb event.

Region 501 (formerly known as Region 484 last month) has also increased
in activity over the last 48 hours, producing numerous smaller (but
significant) M-class flares. An event on 17 November was associated with a
coronal mass ejection that is directed at least partially Earthward. Impact
of that disturbance could happen near the mid UTC hours of 19 November (as
early as tonight for eastern North Americans). Its arrival could
herald enhanced levels of auroral activity for many dark-sky middle latitude
observers.

Region 501 also produced a second influential solar flare a few hours
ago (just prior to the large solar flare on the eastern limb) that will
almost certainly help prolong auroral activity into 21 November when the
associated coronal mass ejection reaches the Earth.

A mid-latitude aurora watch is active for 19-20 November and will
probably be extended through 21 November. The watch has been appended below.

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MIDDLE LATITUDE AURORAL ACTIVITY WATCH

WATCH EXTENDED: 12:10 UTC, 18 NOVEMBER 2003

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VALID BEGINNING AT: IN-PROGRESS
EXTENDED UNTIL: 23:00 UTC (7 pm EDT) ON 20 NOVEMBER

PREDICTED IMPACT TIME OF DISTURBANCE: NEAR 09:30 UTC ON 19 NOVEMBER
(+/- SEVERAL HOURS)

HIGH RISK PERIOD: 19 NOVEMBER (UTC DAYS)
MODERATE RISK PERIOD: 19 - 20 NOVEMBER

PREDICTED ACTIVITY INDICES: 24, 40, 24, 20 (18 NOVEMBER - 21 NOVEMBER)

POTENTIAL MAGNITUDE OF MIDDLE LATITUDE AURORAL ACTIVITY: MODERATE

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

MINOR BELT = 12 TO 24 HOURS

ESTIMATED OPTIMUM OBSERVING CONDITIONS: NEAR AND PRIOR TO LOCAL MIDNIGHT

EXPECTED LUNAR INTERFERENCE: LOW AFTER MOONRISE (AFTER LOCAL MIDNIGHT)

OVERALL OPPORTUNITY FOR OBSERVATIONS FROM MIDDLE LATITUDES: FAIR

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

WASHINGTON STATE TO SOUTHERN MONTANA TO SOUTH DAKOTA TO SOUTHERN MINNESOTA

TO SOUTHERN MICHIGAN TO DARK-SKY SITES OF NORTHERN PENNSYLVANIA TO DARK

SKY SITES OF NEW HAMPSHIRE.

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

SCOTLAND AND POSSIBLY NORTHERN IRELAND/CENTRAL U.K. TO EXTREME NORTHERN

NETHERLANDS TO EXTREME NORTHERN GERMANY TO SOUTHERN SWEDEN TO LATVIA TO

ESTONIA TO NORTHERN RUSSIA.

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

SOUTHERN NEW ZEALAND TO EXTREME SOUTHEASTERN AUSTRALIA (VICTORIA).

SYNOPSIS...

A partial halo coronal mass ejection (in our judgement, a possible full
faint halo event) was observed on 17 November following a class M4.2/1N solar
flare from sunspot complex 501. Impact of this disturbance could occur during
the early to mid UTC hours of 19 November. The Space Environment Center
believes it may arrive on 20 November or perhaps late in the UTC day of 19
November. There are discrepancies in some of the data associated with this
event that are introducing larger than normal error-bars in the predicted
impact times. Nevertheless, it is our opinion that the CME will likely impact
the Earth near 09:30 UTC, give or take several hours.

Another relatively large solar flare was observed just prior to the time
of issue of this watch, again from Region 501 (with later contributions from
an unnumbered region behind the southeast limb - probably returning Region
486). This event from Region 501 is also probably associated with an
Earthward-directed coronal mass ejection. As a result, this watch will
probably be extended another 24 to 48 hours after this last event has been
analyzed.

There is the potential for periods of moderate to strong auroral
activity over the high and many middle latitude regions on 19 and 20
November. If the shock arrives near STD's predicted time, observations will
be best for the New Zealand and Australian regions followed by Europe a few
hours later. If SEC is more accurate, North America and Europe should be best
positioned.

This watch will remain valid through 23:00 UTC (7 pm EDT) on
20 November. It will then be updated or allowed to expire. For updated
information, visit: http://www.spacew.com/aurora/forum.html. For real-time
plots of current activity, visit: http://www.spacew.com/plots.html or
www.sec.noaa.gov.