Folks:
What an exciting time for radio enthusiasts! This past weekend's media hype
about a major geomagnetic and solar storm was unfortunate and unwarranted.
But,
today, solar events have occurred that has the whole propagation science
community buzzing.
I just finished talking with Mike Weaver from the National Ocean and
Atmospheric
Administration Space and Environment Center (NOAA SEC). He is the Solar
Forecaster that has been on duty for the last four days. Last week, I also
spoke with Bill Murtagh, who is beginning a shift to cover the next few days.
Our discussion focused on today's events, and what will transpire over the next
few days. The following is my perspective of current solar and geophysical
conditions and the forecast for the next 48 hours or so.
On 28 October 2003 UTC, an X17.2-class flare from NOAA Region 486 occurred at
0951Z, peaking at 1110Z. This caused severe radio blackouts (R4 is the
reported
level, see http://www.sec.noaa.gov/NOAAscales/ for details on the scales used)
on the sunlit side of the Earth (which would have been morning, on the eastern
coast of North America). It also created an S3 (strong) solar radiation storm.
Associated with this flare are a proton event and a full-halo coronal mass
ejection (CME). This flare is the second most intense of the current solar
cycle. It is not historical. We expect several of these large flares during
any given solar cycle.
The proton event started at about 1330Z, and has exceeded all threshold levels,
causing a Polar Cap Absorption event (PCA). It is expected that this proton
event will be prolonged and last for the next 36 hours, to some degree. This
will cause transpolar path degradation (don't expect any DX over the poles nor
over any high-latitude paths) for the next few days.
The CME was a full-halo, and is directed squarely at the Earth. Based on the
speed and recordings, so far, Mike expects it to impact the Magnetosphere at
about 1500Z 29 October 2003. When it hits, the shock alone will produce at
least G3-level geomagnetic activity. This would translate to a Kp index of
about 8, even if the IMF (Interplanetary Magnetic Field) is not pointed south
when the CME arrives. After the initial shock wave, if the Bz is negative,
indicating that the IMF has turned south, the Kp index will remain high, with a
possible Kp of 9 during the passage of the CME. This will cause between a
level
G4 and a G5 (severe to extreme) geomagnetic storm. This will severely degrade
HF and MW radio communications (while possibly enhancing VHF/UHF propagation).
The timing of the arrival of the CME shock will occur after sunrise for those
in
North America. Therefore, I do not expect to see any Aurora tonight, local
time
on 28 October 2003. However, I do expect radio auroral mode propagation during
the day of 29 October 2003, and continuing into the night of the same day. If
the IMF remains negative, there is a strong chance of a prolonged severe
geomagnetic storm, with associated Aurora viewable as far south as southern
California and Florida.
Continued radio blackouts are likely from new flare activity. As I write this,
we are in the decline of a new M-class flare. There are eight main regions on
the visible solar disk, three of which are actively producing flares. One of
these is about to rotate out of view. One of the new regions just rotating
into
view is active, and has already produced some M-class flares.
Overall conditions:
In the next 12 to 20 hours, expect great conditions on frequencies above 15
MHz,
while in general, all HF will have periods of radio blackouts during the flare
events, if they occur. (And, they will occur). Sometime around 1500Z,
tomorrow
(29 Oct 2003), expect all HF communications to become severely degraded with
the
arrival of the CME shock, and for a severe to extreme geomagnetic storm to
commence and last for a prolonged period. S3-level (severe) solar radiation
storm conditions will last for the next 24 to 48 hours.
I expect a lot more activity during this week, but I don't view this as a
"third" peak in this current solar cycle, number 23. Several past cycles have
had such bursts during the decline of those cycles.
I'll post more about this soon.
73 de Tomas, NW7US (AAR0JA/AAM0EWA)
--
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