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From: oler@rho.uleth.ca (Cary Oler)
Reply-To: SOLAR-WARNINGS Distribution List <solar-warnings@lut.fi>
To: SOLAR-WARNINGS Distribution List <solar-warnings@lut.fi>
Message-Id: <9302171829.AA17154@rho.uleth.ca>
Subject: ALERT: Major Solar Flare Alert
Date: Wed, 17 Feb 93 11:29:39 MST
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Status: OR

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                           MAJOR SOLAR FLARE ALERT

                        ISSUED: 18:00 UT, 17 FEBRUARY

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                        * NIL to Low Impact Possible *


MAJOR ENERGETIC EVENT SUMMARY:

            ( All times are valid for the UT day of 17 February )

Flare Size: Class M5.8/SF
  Location: N18E04 (Region 7425)
  Tenflare: None reported.
SESC Times: Begin=17/1032 UT, Peak=17/1040 UT, End=17/1058 UT
            (SESC Times are based on a half-power-point system)
    Sweeps: No Sweeps Reported


PRELIMINARY X-RAY TIME PROFILE DATA AND ESTIMATED STATISTICS:

BEGIN (XRAY)   MAX  (XRAY)   END  (XRAY)   DURATION   INTEG. FLUX   SWF DUR.
------------   -----------   -----------   --------   -----------   --------
 1032 (C1.5)   1040 (M5.8)   1152 (C9.9)   079 MIN.   0.114 J/m^2    076 min

NOTE:  The xray time profile data above is not based on the half-power-point
       system, but is intended to give a general idea of the duration of the
       entire event, from the start to the end when xrays fall below M-class
       levels.  Integrated x-ray flux covers the interval from start to end.


SYNOPSIS:

     It appears this major flare was the result of simultaneous flaring from
Regions 7420 and 7425.  Region 7420 is on the west limb and produced an
optically small flare while Region 7425 (which is near the central meridian)
generated a flare of its own.  The combined x-rays from these flares are
thought to have been sufficient to push x-rays above the M5 threshold.  More
detail will be made available in the daily activity summary for 17 February.

     In x-rays, this flare had a fairly impressive long-decay signature, but
lacked significant radio activity.  There were no reported Type II or IV
sweeps and only weak discrete radio emissions.  A moderate short wave fadeout
accompanied this flare that affected frequencies to about 12 or 15 MHz.


POTENTIAL TERRESTRIAL IMPACT ASSESSMENT:

     The following tables depict the preliminary estimated potential for
terrestrial impacts in various categories.  These tables are valid only for
the flare described and do not include assessments for previous influential
flare events.


                      ----------------------------------
                      POTENTIAL MAGNITUDE OF DISTURBANCE
                      ----------------------------------
                                 HIGH : 01 %
                             MODERATE : 10 %
                                  LOW : 35 %
                                 NONE : 54 %
                      ----------------------------------
                      OVERALL ARRIVAL PROBABILITY : 40 %


              ESTIMATED WINDOW OF SHOCK ARRIVAL IF SHOCK ARRIVES
    ---------------------------------------------------------------------
   |  MINIMUM   |    EARLY     |  PREFERRED  |     LATE     |  MAXIMUM   |
   |------------|--------------|-------------|--------------|------------|
   | 18/2100 UT |  19/0200 UT  | 19/1000 UT  |  19/1800 UT  | 19/2300 UT |
   |  FEBRUARY  |   FEBRUARY   |  FEBRUARY   |   FEBRUARY   |  FEBRUARY  |
   |------------|---------------------|---------------------|------------|
   |     5 %    |  45%  PROBABILITY   |  45% PROBABILITY    |     5 %    |
    ---------------------------------------------------------------------


---------------------------------       ----------------------------------
  POTENTIAL FOR >10 MEV PROTONS           POTENTIAL FOR >100 MEV PROTONS
---------------------------------       ----------------------------------
    HIGH FLUX :  0 %  > 100 PFU             HIGH FLUX :  0 %  > 100 PFU
MODERATE FLUX : 15 %  >  10 PFU         MODERATE FLUX :  0 %  >  10 PFU
     LOW FLUX : 30 %  >   1 PFU              LOW FLUX :  0 %  >   1 PFU
         NONE : 55 %  <=  1 PFU                  NONE :100 %  <=  1 PFU
----------------------------------      ----------------------------------
OVERALL ARRIVAL PROBABILITY: 20 %       OVERALL ARRIVAL PROBABILITY: 0 %

---------------------------------       ---------------------------------
EST. POTENTIAL GEOMAGNETIC IMPACT       EST. POTENTIAL IONOSPHERIC IMPACT
---------------------------------       ---------------------------------
       SEVERE STORM :  1 %                 LOW LATITUDES : NIL
        MAJOR STORM : 10 %              MIDDLE LATITUDES : NIL - MINOR
        MINOR STORM : 40 %                HIGH LATITUDES : NIL - MINOR
     ACTIVE OR LESS : 49 %               POLAR LATITUDES : NIL - MINOR
---------------------------------       ---------------------------------
 PROBABLE SI ASSOCIATION : 40 %       ESTIMATED GLOBAL IMPACT: NIL - MINOR


ESTIMATED POTENTIAL DURATION OF DISTURBANCE AFTER ARRIVAL: 18 TO 32 HOURS

EST. PROBABILITY FOR GEOSYNCHRONOUS SATELLITE MAGNETOPAUSE CROSSINGS:  20 %


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