AstroAlert: Significant Solar Limb Activity In-Progress

[Peter Kuklok]

A s t r o A l e r t

Sun-Earth Alert

Solar Terrestrial Dispatch

http://www.spacew.com

20 July 2002

A MOVIE of this event is available:

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

Watch solar activity in real-time:

http://www.spacew.com/sunnow

(updated every minute)

SIGNIFICANT SOLAR LIMB ACTIVITY IN PROGRESS

As noted in the AstroAlert of 19 July, there exists a potential for
significant solar activity visible on the east limb of the Sun. Over the last
24 hours, frequent surging has been observed as the strongly active sunspot
complex just behind the eastern limb of the Sun begins to rotate into view.

Today, at 21:30 UTC (5:30 pm EDT), a very strong class X3.3 solar x-ray flare
was observed from this sunspot complex. Although the sunspot complex itself
is not yet visible, the activity it is producing is visible.

Big Bear Solar Observatory (BBSO) and the Culgoora Solar Observatory
(Australia) were able to image todays activity. See the following URL:
http://www.spacew.com/astroalert.html for images and a movie of the activity.

This spot complex is due to rotate into view within approximately the next 24
to 48 hours. It has been producing energetic solar activity about once every
other day during the last week. Until the spot complex rotates into view so
we can ascertain it's growth/decay and magnetic characteristics, it is
reasonable to assume that this frequency of activity from this spot complex
may persist. As a result, this may be one of the best opportunities of the
solar cycle to observe energetic limb activity through telescopic equipment
equipped with suitable filters.

Frequent surging is expected as this spot complex moves onto the east limb.
Limb sprays are possible and post-flare loop prominence arcades are virtually
a certainty if this region produces another major flare while near the east
limb.

DETECTING SOLAR FLARES WITHOUT TELESCOPES

If you don't own a telescope, you can still "observe" these events if you
have an inexpensive short wave radio receiver. The intense solar x-rays from
these flares are entirely absorbed by the lower layers of the Earth's
protective ionosphere (known as the D-region of the ionosphere). During this
absorption process, the lower region of the ionosphere becomes much more
heavily ionized than normal. Under normal conditions, short wave radio signal
energy travels from a transmitter on the ground up to the ionosphere where it
is reflected back to the ground a large distance away. During major solar
x-ray flares, the lower portion of the ionosphere becomes so heavily ionized
that short wave radio signals lose all of their strength when they pass into
this intensely ionized region. The result is known as a short wave radio
blackout. By listening to radio stations via short wave radio, you can
instantaneously detect these strong solar flares by noticing a weakening (or
a complete loss) of signal strength. Simple short wave radios capable of
receiving broadcasts from popular radio stations such as the Voice of America
are inexpensive and can be found at many Electronics stores. You don't even
require an elaborate antenna - the one supplied with the radio should suffice
in most cases.

A simple short wave radio receiver is capable of detecting minor M-class
solar x-ray flares to major M and X-class solar flares. The position of the
Sun has a strong bearing on the impact of the signal loss you observe. If the
radio signal you are listening to originates from a location that would take
the radio signal through sunlit portions of the Earth, you would be able to
detect signal loss during solar flare activity. But if the Sun is setting and
the radio station you are listening to originates at a location that is still
in darkness (further east of you), you won't be able to detect flare
activity. So to properly detect solar x-ray flares, you must make certain the
radio station you are listening to is either in a sunlit region of the Earth
or is transmitting to you through an area of the Earth that is Sunlit. To
help you visualize the region that is sunlit, the Space Environment Center
makes available a regularly updated (real-time) map that shows the region of
the Earth where flare-induced ionization is strong and the radio frequencies
that may be affected by the event. The map associated with today's X-class
solar flare is available at: http://www.spacew.com/astroalert.html

For those interested in detecting flares using short wave radio, purchase a
short wave radio and tune it to stations like the Voice of America.
Regularly updated frequency schedules for Voice of America are available
on their web site (visit www.spacew.com/astroalert for details). Many other
stations also exist that would work equally well. Just tune through the bands
and find something of interest. If you are in a day lit region of the Earth,
the signal is most likely reaching you through an ionospheric bounce and will
work well for monitoring solar activity.

Solar x-ray flares more rapidly and more easily affect the lower frequencies
below 10 to 15 MHz, so try to find stations below 10 or 15 MHz in frequency
if you try this method of detecting flare activity. The length of time that a
station remains inaudible during the day reflects the strength and/or
duration of the solar x-ray flare. Some significant X-class solar flares in
history have produced radio blackouts that have lasted from sunrise to near
sunset.

** End of the AstroAlert Bulletin **

[Peter Kuklok]

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MAJOR SOLAR FLARE ALERT

ISSUED: 00:50 UTC, 21 JULY 2002

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

A major class X3.3 solar flare was observed at 21:30 UTC on 20 July.
This event was accompanied by strong radio emissions (a 2600 sfu tenflare,
20,000 sfu intensity at 8.8 GHz and 43,000 sfu at 15.4 GHz), a Type II
sweep (estimated shock velocity 515 km/sec - preliminary), and a strong loop
prominence on the southeast limb. In addition, an interesting and h-alpha
wave is visible propagating onto the visible solar disk to the northwest of
the flaring center. Although this is well time correlated with the presumed
onset of the flare start, it may be an independent phenomena as opposed to a
Moreton-type wave related directly to the flaring site. Nevertheless, it is
interesting to speculate.

The x-ray and radio signatures of this event suggest it was a probable
proton producing flare. However, no significant flux enhancements are
expected in the near-Earth space environment due to its present poor
location. X-ray fluence with this event was modestly respectable at near
0.75 Joules.

The southeast limb has been teeming with activity. Frequent and
occasionally fairly strong surging has been observed over the last 24 hours.
Additional major levels of solar flare activity are expected from this spot
complex as it continues to approach and (within the next 24 to 48 hours)
rotate into view.

Region 10036 is still considered a possible site for major flaring. It
has experienced renewed growth over the last 24 hours. Although magnetic
gradients and shear are not as strong as in Region 10030, the spot complex
may still produce an isolated major event over the next several days. Flare
activity from Region 10036 is expected to be fairly infrequent unless more
rapid growth and dynamic flux emergence occurs. It is expected to take a back
seat to the activity in the region due to rotate around the southeast limb.

** End of Notice **

[Ulrich Rieth]

Protonen am GOES reagieren *o.T.*