
From: std_oler@HG.ULeth.CA
To: haminfo@lut.fi
Subject: POTENTIAL MAJOR FLARE WARNING - 19 FEBRUARY
Date: Tue, 19 Feb 91 01:33:45 MST

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                     POTENTIAL MAJOR FLARE WARNING
 
                         ATTENTION  ATTENTION
 
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                          February 19, 1991
 
 
ATTENTION:
 
     There is a distinct possibility for major flaring to occur within the
regions now near the eastern limb.  There is an elevated risk for potential
X-class and/or major proton flares from the regions now returning to
the east limb.  Although the occurrence of any major flares from the eastern
regions are still fairly incapable of producing significant terrestrial
impacts aside from potentially strong SID's and SWF's, the risk for major
flaring is high enough to warrant a potential major flare warning.  This
warning will almost certainly remain in effect throughout the coming week
(19 - 26 Feb) at least, and probably into the second week as well (26 Feb
to 06 March).  Major flaring is expected to occur over the next two weeks.
 
     Major flaring could begin to be observed within the next 72 hours.
Sudden ionospheric disturbances (SID's) and shortwave fading (SWF's) could
become abnormally intense and of long duration should major flaring occur.
 
     Several active regions are returning into view near the eastern limb.
One region, now visible and identified as Region 6509, is of large size and
appears to be moderately complex.  Magnetic measurements of this region are
not yet reliably accurate due to its proximity to the east limb.  M-class
flaring has increased significantly over the past 48 hours.  Four M-class
flares were observed on 18 February.  Two of these flares originated from
Region 6504 (S16E36); a class M2.6/1N at 07:30 UT, and a class M1.0/SF at
22:07 UT.  Both of these flares are suspected of producing minor SID's/SWF's.
The other two M-class flares were optically uncorrelated, which points to
the possibility that another active region is around the eastern limb
spawning these events.
 
     The solar flux increased dramatically today to 267, which is a huge
jump of 53 points compared to yesterdays flux value of 214.  This single
day increase in the solar flux may represent further evidence to suggest
that a potentially significant active region is ready to rotate into view.
We will soon know just how significant the activity just behind the eastern
limb is.  An optical region responsible (at least, in part) for the large
increase in the solar flux should become visible on 19 February.  This would
coincide with the expected return of old Region 6471, which became very
active just as it departed the western limb two weeks ago.  A better
analysis of the regions on the eastern limb will be possible by about 21
February.  An additional bulletin may be posted near this time if activity
proves to be unusually energetic or complex.
 
     The solar activity prediction chart given in the latest STFR report
has obviously been invalidated with todays unexpectedly high increase in
the solar flux.  Rough predictions for the next 72 hours suggest a further
dramatic increase in the solar flux to 340 by 21 February.  Further increases
to near 360 (or higher) are possible in the days following.  The sunspot
number broke 300 again today and was measured at 301 on 18 February.  The
sunspot number could reach (or possibly briefly exceed) 400 before this
week ends.  The background x-ray flux increased again to a class C2.7
x-ray level on 18 February.
 
     Widespread openings on 6 meters will be possible over the next two
weeks if solar indices reach the levels anticipated.  Solid communications
on the high HF bands will also be possible throughout the next two weeks.
However, frequent flare-induced SID's will cause some periodic distortion
and fading over the sunlit portions of the earth.
 
     Watch for possible major flare alerts.
 
 
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