[HIham] Propagation Currently/Immediate Days Ahead

[Jim Reid]

Aloha,  following from the Topband reflector today,
was posted by the Propagation Editor, CQ/CQ VHF/Popular
Communications Magazines,  Tomas, NW7US:

"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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