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From: oler@HG.ULeth.CA
To: haminfo@lut.fi
Subject: MAJOR SOLAR FLARE ALERT - 25 FEBRUARY
Date: Mon, 25 Feb 91 18:02:31 MST

                        --  MAJOR SOLAR FLARE ALERT  --
 
                               FEBRUARY 25, 1991
 
                              Flare Event Summary
                           Potential Impact Forecast
                        SATELLITE PROTON EVENT OCCURRED
 
 
                                    --------
 
 
MAJOR ENERGETIC EVENT SUMMARY
 
     A major proton flare exploded off the southwest limb today.  The event
began at 08:06 UT, peaked at 08:19 UT and ended at 09:51 UT on 25 February.
The flare was rated a class X1.2/2N Tenflare and was associated with strong
Type II, III and IV sweeps.  Rich radio emissions were observed from this
flare.  Solar protons arrived and produced a satellite proton event at
12:10 UT on 25 February.  The event was short-lived, however, and
officially ended a little over an hour later at 13:35 UT on 25 February.
 
     This major X class flare was spawned by Region 6497 which is now
crossing behind the western limb.  The largest regions on the disk (6509
and 6508) are relatively dormant, despite their Beta-Gamma magnetic
configuration.
 
POTENTIAL TERRESTRIAL IMPACT FORECAST
 
     This flare was a major event and did produce a coronal mass ejection,
as is evident by the strong Type II and IV sweeps which were observed.
However, this flare was near the western limb and therefore probably will
not produce anything too significant in the way of terrestrial impacts.
There is some uncertainty regarding this, however, as events which occur
near the vernal equinox can become amplified more than expected.

     Preliminary analysis suggests that there is a moderate possibility
that planetary geomagnetic activity could increase to near minor storm
levels on 28 February.  An increase in activity is likely, but the
amount of coupling which takes place is uncertain.
 
     Geomagnetic activity is expected to increase on 28 February to
planetary A-index values between 20 and 35 for middle latitudes.  A lesser
impact over lower latitudes will likely be observed.  High latitudes will
suffer the worst conditions, with low to moderate intensity minor storming
occurring on 28 February (A-index values between 25 and 38).  Middle
latitude K-indices could range from 3 to 5 on 28 February.  High latitude
K-indices could range from 4 to 7.  Magnetic fluctuations between 400 and 750
gamma could be observed over high latitudes, while middle and low latitudes
will likely witness magnetic fluctuations between 55 and 140 gamma.
 
     Auroral activity will be most intense over the high latitudes and
extreme northern middle latitudes.  There is a very slight chance that the
impact from this flare could be higher than expected, perhaps with brief
periods of major storming over middle latitudes.  Please note that this is
not very likely, but is slightly possible.  If impacts are greater than
expected, auroral activity could become visible over the northern latitudes
north of about 42-44 North latitude.
 
     HF propagation should remain above normal until sometime on 28
February when the interplanetary shock is expected to arrive.  An SSC
should be observed with the passage of this shock, sometime on 28 February.
Thereafter, MUF's should drop combined with increased fading and absorption
(particularly over the middle to high latitudes).  High latitude propagation
has become degraded due to a polar cap disturbance which commenced on 24
February and remains in progress.  Things could get significantly worse
over the higher latitudes on 28 February if we are in fact affected by this
flare.  Polar propagation paths will suffer strong absorption and strong
flutter and fading if terrestrial impacts materialize.
 
     There is a chance for VHF auroral backscatter conditions to
materialize over the middle and high latitudes on 28 February, particularly
during the late afternoon hours and again near midnight.  However, signal
qualities will likely become degraded for most VHF DX signals over the middle
and high latitudes.
 
     A recovery is expected on 01/02 March to generally unsettled
conditions.  We are nearing the vernal equinox now, so geomagnetic activity
should become a bit more active soon.  A potential geomagnetic storm warning
may be issued within the next 24 hours.
 
     There is a slight risk for another major flare from Region 6497.  This
risk may exist for the next 24 hours (until 27 February).  No major flares
from the larger regions on the disk are currently anticipated.  Low-level
M-class flaring could occur from Region 6504, 6508 or 6509.
 
 
**  End of Alert  **
 

