Subj: AstroAlert: Middle Latitude Auroral Activity Watch - 11-14 May
Date: 5/9/00 9:44:23 PM Pacific Daylight Time
From: firstname.lastname@example.org (Cary Oler)
A s t r o A l e r t
Solar Terrestrial Dispatch
Valid: 11-14 May (UTC days)
with emphasis for 11-13 May
-- Potential Category G2 Geomagnetic Storm --
Solar filaments are enormously large and dark strings of material that
are suspended above the backdrop of the Sun's surface by powerful magnetic
fields. When observed on the limbs of the Sun against the black background of
space, they appear as bright clouds of material (known as prominences) that
appear to hang magically above the surface of the Sun. Prominences and
filaments are therefore different words used to describe the same physical
On 06 and 07 May, some interesting and potentially influential
filamentary activity occurred on the Sun. Several small filaments disappeared
as well as one very large and dense filament. These disappearances occur when
the magnetic fields that hold the mass above the surface of the Sun becomes
disrupted. With the magnetic fields disrupted, the suspended mass is no
longer firmly held in place. The magnetic fields begin to rise outward into
space along with the imprisoned mass. Eventually, the mass is ejected into
interplanetary space and becomes a coronal mass ejection (or CME).
On 06 and 07 May, the disappearance of several filaments resulted in a
mass ejection which has been determined to contain an Earthward directed
component. This coronal mass ejection is predicted to impact the Earth
sometime during the mid to late UTC hours of 11 May. The mass is not thought
to be travelling at a very high velocity. As a result, it will take longer
for the cloud of material to pass through the Earth system. Forecasters
estimate the duration of this disturbance may be in the neighborhood of about
36 to 48 hours, commencing sometime on 11 May.
Although the velocity of the ejected mass is not very high, there is a
chance the magnetic fields associated with the ejected mass may be oriented
favorably for increasing levels of goemagnetic and auroral activity at the
Earth to near minor storm levels, with possible brief periods of major
storming over the high latitude regions.
For these reasons, we are issuing a middle latitude auroral activity
watch to cover the time period spanning from the early UTC hours of 11 May to
14 May, but with heaviest emphasis on the UTC days of 12 and 13 May which
should correspond to the interval of strongest auroral activity.
This auroral activity disturbance will NOT likely reach levels of
intensity similar to those observed during the memorable aurora storm of 06
April. A somewhat subdued disturbance is a more realistic expectation, with
possible bursts of activity that may become more easily visible over fairly
widespread middle latitude regions. The northern tier of U.S. states may
observe activity, as well as extreme northern regions of Europe and Russia.
New Zealanders as well as observers in extreme southeastern parts of
Australia may also spot periods of activity.
The approximately > 50% illuminated waxing moon will interfere with
attempts to view activity until after local midnight when the moon continues
its travel toward the horizon. Observations near 3 am may be most productive,
during the time when the moon begins to set and the sky becomes darker.
Anyone who believes they may have spotted auroral activity are
encouraged to report their findings to:
A near-real-time updated list of observations reported through this form
page is available from:
Individuals with an appetite for photography may want to try
photographing this activity, even if no activity is visible with the naked
eye. Very often auroral activity becomes visible to the sensitive films of
cameras that is not visible to the naked eyes. During the anticipated height
of the storm, take a few extended exposures of the northern horizon (for
northern hemisphere observers) or southern horizon (for observers in the
southern hemisphere). Try various exposure settings ranging in time from
perhaps 10 seconds to a full minute or more using a stable camera tripod.
Experiment with various settings and use the widest angle lense you have to
better capture more of the sky during the exposure. Try to find a location
where the northern (or southern) horizons are free from light pollution. You
may be surprised to find auroral activity visible on the film that you never
observed with your eyes.
** End of AstroAlert **