[CC-ARES-RACES] Severe storm - still!

[JD Delancy]

Guess HF conditions will be bad for a while..

------------Original Message------------
Subject: Severe storm - still!
   Date:  Thu, 23 May 2002 18:21:24 -0600 (MDT)
   From:Paul Harden <pharden@aoc.nrao.edu>

Gang,
A severe geomagnetic storm remains ongoing at 2400UTC, although it is
expected to start diminishing this evening.  It has caused near blackout
conditions globally on the HF bands.  Todays estimated A-index is at
least 50, with the K-indices since the onset being K=5,7,7 and 5.

Yesterday morning (wednesday), there was a long duration flare event from
an active region nearly at the sun's center.  It produced two M-class and
a C-class flare, about 2-3 hours apart.  When a solar flare occurs, several
things happen.  First is the "speed of light" radiation that leaves the
sun and hits the earth for about the duration of the flare event ... 
which in this case was several hours.  This tends to ionize the E and F 
layers.  This is actually good, in that it emhances the reflectivity to
radio waves for good skip propagation and low losses ... especially
important to QRP operators.  So for a good hint, get on the higher
frequencies shortly after a flare event to take advantage of several hours
of some "hot" conditions on 10-15M, and sometimes 6M.

But that bad thing about this ionizing radiation from a flare is if the
radiation is strong enough, it will penetrate through the E and F layers
and ionize the D-layer as well.  This is NOT good!  The D-layer is the
"absorption layer" in that the more it is ionized from sunlight, the more
attenuation it offers to HF signals.  So if the ionizing radiation from a
flare were to highly ionize the D-layer, it would highly attenuate HF
signals for very poor conditions (near blackout conditions) or even to a
full blackout situation.  Fortunately, this usually only lasts for a short
time (hours or less).

Another thing that happens with a large flare, is to understand it is a
huge explosion on the sun's surface, and as with any explosion, it produces
a large shock wave.  The shockwave from a flare carries millions of tons of
solar mass and tosses it out into space.  This is called a Coronal Mass
Ejection or CME.  A CME is simply this shockwave of matter being flung out
into space.  If the trajectory is right, then the shockwave will hit the
earth.  Only about 20-30% of the CME's actually hit the earth.  For the
shockwave to hit the earth, the CME must be originated from NEAR the center
of the sun.

Most shockwaves from flares travel towards the earth about 700-1200 km/sec.
and thus takes about two days to get here.  When the shockwave does arrive,
it is a very sudden, huge blast of solar wind smacking up against our
magnetic field.  This causes our magnetic field to be compressed inward
from the enhanced solar wind and starts it to wiggle like Jello.  As it
wiggles, it generates huge electrical currents that flows along our magnetic
field lines.  This is the dynamo effect, generating electricity by moving
metal through a magnetic field ... or in this case, moving a magnetic
field around stationary metal (which would be the earth itself, power lines,
phone lines, YOUR ANTENNA, etc.).  This electrical current generates gobs
of noise.  THIS IS THE BUZZING NOISE ON HF MANY OF YOU HAVE REPORTED HEARING.
The earth's generator at work as our magnetic field is wiggling.

In today's case, this gemagnetic storm is the result of the 3 large flares
that occured yesterday, all from the same active region on the sun, and
producing 3 separate and distinct CME's.  You can see these 3 CME's leaving
the sun at:
www.spaceweather.com
A small video shows it on the home page, upper right corner.  Neat.

So instead of the shockwave from a CME hitting the earth triggering a
geomagnetic field, THREE CME's are smacking the earth, one behind the
other, to keep our magnetic field wiggling pretty good.  Although to be
fully accurate, the LASCO satellite detected only two shockwaves this
morning, not three, meaning the velocity of the 3rd shockwave was likely
less than the current solar wind at the time.  The first shockwave arrived
about 1000UTC, bumping the solar wind up to about 600 km/sec.  Three hours
later (1300UTC), the 2nd shockwave arrived, with a sudden increase in the
solar wind to 1000 km/sec.  2-3 hours later, the background solar wind was
still in the 700-800 km/sec range, likely masking the 3rd CME shockwave.

This is a rare occurance, and nobody knows quite how to forecast it.
Some believe the "3 shots across the bow" will keep the geomagnetic storm
going all night.  Should this be the case, be on the lookout for AURORA
THIS EVENING in the Northern U.S., and perhaps even well into the south.
The K=7 suggests a fairly southern aurora ... but of course not down to
Florida or Cuba or anything (sorry Arnie!).  

Others believe the signs are already here that the storm is subsiding,
by the fact the K index has dropped from 7 to 5 over the last 3 hour
reporting period.  This could mean the storm is winding down and aurora
into the middle U.S. would be unlikely.

The effects of a geomagnetic storm worsen the lower in frequency you go,
so the upper bands, such as 10M if open, is scarcely effected, but 20M
and below is pretty much wiped out.  So as the storm subsides, the upper
bands will clear up first.  It takes VERY LITTLE storming to mess up 40M,
for example :-(  as most of you have probably noticed.  

Anyway, that is a fairly short but hopefully succinct description of a
solar storm, and the following geomagnetic storm, and a little of the
physics behind it, for those of you new to QRP-L.

For current conditions, see:  www.sec.noaa.gov/today.html

The top of the page shows the current x-ray emissions from the sun, which
indicate FLARE activity.  Right now that part is pretty quiet.  Below that
is the earth environment, showing proton energy levels and the K-index.
The elevated 10Mev Protons right now is giving our friends in Canada even
a worse set of conditions that we have here, if you can believe that.
And the K-index is shown on the bottom graph, updated every 3 hours.  RED
bars indicate major storming (K=4) to severe storming (K5) to extreme
storming (K=7,8,9).

Geomagnetic storms are not the end of the world.  Turn the radio on now
and again and check conditions.  Either you won't hear anything (severe
storming/blackout), or very weak signals (major storming), or weird
propagation.  The weird propagation means you can sometimes hear very
distant DX stations quite loud, while everything else is kinda weak.  Hey,
grab 'em while you can.

Lastly, HF conditions tend to get very quiet and stable right after a
large geomagnetic storm.  This is always a good time to get on the air,
a day or two after a large storm, to take advantage of very quiet conditions
and good DX propagation.  This could imply good conditions this weekend for
the various contests.

72, Paul NA5N

National Radio Astronomy Observatory
VLA/VLBA Radio Telescopes
Socorro, New Mexico