:Product: 19980825RSGA.txt
:Issued: 1998 Aug 25 2200 UTC
# Prepared jointly by the U.S. Dept. of Commerce, NOAA,
# Space Environment Center and the U.S. Air Force.
#
JOINT USAF/NOAA REPORT OF SOLAR AND GEOPHYSICAL ACTIVITY
::::::::: CORRECTED COPY ::::::::::
SDF NUMBER 237 ISSUED AT 2200Z ON 25 AUG 1998
IA.  ANALYSIS OF SOLAR ACTIVE REGIONS AND ACTIVITY FROM  24/2100Z
TO 25/2100Z:  SOLAR ACTIVITY HAS BEEN HIGH.  A MAJOR SOLAR EVENT
BEGAN AFTER 24/2100 UT.  THE ACTIVITY INCLUDED A CLASS X1 X-RAY
EVENT BEGINNING AT 2150 UT AND PEAKING AT 2212 UT.  AN OPTICAL
FLARE CLASS 3B BEGAN AT 2148 UT AND PEAKED AFTER 0108 UT.  THE
ASSOCIATED OPTICAL EVENTS INCLUDED DISAPPEARANCE OF A MODERATELY
LARGE ACTIVE REGION FILMENT AND MAJOR UMBRAL COVERAGE BY THE FLARE
EMMISSION IN H-ALPHA.  POST-FLARE LOOPS WERE REPORTED.  MAJOR RADIO
BURSTS EXTENDED FROM 70 MHZ TO OVER 15,000 MHZ WITH A PEAK FLUX 2100
SFU AT 2695 MHZ.  THE EVENT WAS TYPICAL OF THOSE LABELED "BIG
FLARES."   ACTIVE REGION 8307 (N30 W05) IS CLASSIFIED AS CKO WITH A
SIMPLIFYING MAGNETIC FIELD ACCORDING TO THE TREND OF REPORTS FROM
SOLAR OBSERVERS.  AN ACTIVE FILAMENT THAT WAS INVOLVED IN THE ACTIVITY
YESTERDAY HAS REFORMED AND IS AGAIN ACTIVE.
IB.  SOLAR ACTIVITY FORECAST:  THE SLOW RATE OF CHANGE IN REGION 8307
APPEAR TO BE CONSISTENT WITH A GRADUAL SIMPLIFICATION OF THE REGION.
THE PRESENCE OF AN ACTIVE FILAMENT INDICATES CONTINUED CHANCES OF
ENERGETIC ACTIVITY AT ABOUT THE SAME LEVEL AS HAS OCCURRED OVER THE
LAST FEW DAYS.  OTHER REGIONS ON THE VISIBLE DISK MAY GENERATE A FEW
SMALL FLARES.
IIA.  GEOPHYSICAL ACTIVITY SUMMARY FROM 24/2100Z TO 25/2100Z:
THE SOLAR ACTIVITY OCCURRING LATE ON AUGUST 24 PRODUCED A SMALL
PROTON EVENT THAT EXTENDED UP TO INCLUDE VERY ENERGETIC PARTICLES.
GREATER THAN 10 MEV PROTONS BEGAN RISING AT 24/2230 UT AND CROSSED
THE SEC EVENT THRESHOLD AT 24/2355 UT.  FLUXES REACHED A MAXIMUM OF
190 PFU AT 25/0435 UT THEN DECLINED TO ABOUT 100 PFU AND REMAIN
STEADY AT THAT LEVEL.  GREATER THAN 100 MEV PROTONS BEGAN RISING AT
24/2230 AND REACHED EVENT THRESHOLD AT 24/2245 UT.  THESE PEAKED AT
ABOUT 3.5 PFU AT 23/0055 UT BUT CURRENTLY REMAIN ELEVATED AT ABOUT
ONE PFU.  NEUTRON MONITOR DATA AND THE GOES ENERGETIC PARTICLE
SENSOR MEASURING PROTONS ABOVE 850 MEV SHOWED A SMALL RISE BEGINNING
ABOUT 24/2210 UT.  THE THULE RIOMETER HAS REGISTERED BETWEEN ONE AND
TWO DB ABSORPTION SINCE THE PARTICLE EVENT BEGAN. THE GEOMAGNETIC
FIELD HAS BEEN QUIET TO UNSETTLED.  SMALL PERTURBATIONS PASS THE ACE
SATELLITE AT RANDOM INTERVALS OF ABOUT ONE TO TWO HOURS.
MID-LATITUDE K-INDICES HAVE RANGED FROM 1 TO FOUR OVER THE PAST 24
HOURS.
IIB.  GEOPHYSICAL ACTIVITY FORECAST:  A MAJOR GEOMAGNETIC STORM IS
LIKELY TO BEGIN BETWEEN 1200 UT AND 2400 UT ON AUGUST 26.  THE STORM
IS EXPECTED TO BE MOVE RAPIDLY INTO VERY DISTURBED CONDITIONS AND
CONTINUE INTO 27 AUGUST.  THE PASSAGE OF AN INTERPLANETARY SHOCK AT
THE STORM ONSET MAY BE PRECEDED BY A LARGE INCREASE IN ENERGETIC
PARTICLE FLUXES REACHING 2 TO 3 TIMES CURRENT LEVELS.
III.  EVENT PROBABILITIES 26 AUG-28 AUG
CLASS M    35/35/35
CLASS X    15/15/15
PROTON     25/25/25
PCAF       GREEN
IV.  PENTICTON 10.7 CM FLUX
OBSERVED           25 AUG 122
PREDICTED   26 AUG-28 AUG  120/120/120
90 DAY MEAN        25 AUG 117
V.  GEOMAGNETIC A INDICES
OBSERVED AFR/AP 24 AUG  009/011
ESTIMATED AFR/AP 25 AUG  008/010
PREDICTED AFR/AP 26 AUG-28 AUG  080/062-060/065-025/030
VI.  GEOMAGNETIC ACTIVITY PROBABILITIES 26 AUG-28 AUG
A.  MIDDLE LATITUDES
ACTIVE                05/15/30
MINOR STORM           20/50/10
MAJOR-SEVERE STORM    65/26/01
B.  HIGH LATITUDES
ACTIVE                10/15/30
MINOR STORM           25/50/30
MAJOR-SEVERE STORM    60/30/10