Viewing archive of Tuesday, 25 August 1998

Solar activity report

Report of Solar-Geophysical Activity 1998 Aug 25 2200 UTC
Prepared by the NOAA © SWPC and processed by SpaceWeatherLive.com

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 to 28 AUG
Class M35%35%35%
Class X15%15%15%
Proton25%25%25%
PCAFGREEN
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 to 28 AUG
A. Middle Latitudes
Active05%15%30%
Minor storm20%50%10%
Major-severe storm65%26%01%
B. High Latitudes
Active10%15%30%
Minor storm25%50%30%
Major-severe storm60%30%10%

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