:Product: 19980826RSGA.txt
:Issued: 1998 Aug 26 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
SDF NUMBER 238 ISSUED AT 2200Z ON 26 AUG 1998
IA.  ANALYSIS OF SOLAR ACTIVE REGIONS AND ACTIVITY FROM  25/2100Z
TO 26/2100Z:  .SOLAR ACTIVITY HAS BEEN VERY LOW.  X-RAY LEVELS ARE
LOW AND NO ENHANCEMENTS TO CLASS C LEVELS HAVE OCCURRED IN THE PAST
24 HOURS.  ACTIVE REGION 8307 (N31 W15) CONTINUES TO CHANGE VERY
SLOWLY.  THE AREA HAS DECREASED AND THE NUMBER OF SPOTS APPEAR TO BE
DECLINING AS WELL. IT IS CLASSED AS A DKO REGION WITH A BASIC BETA
STRUCTURE AND A REMAINING HINT OF MAGNETIC COMPLEXITY.   AN ACTIVE
FILAMENT CURLS AROUND THE CENTER OF THE REGION AND EXTENDS SOUTHWARD
INTO AN OPEN AREA.   A NEW REGION (8319, N21 E09) WITH AN ACTIVE
ARCH-FILAMENT SYSTEM HAS EMERGED WITHIN THE SCATTERED, REMNANT PLAGE
EAST OF REGION  8307.  BETWEEN THESE TWO REGIONS, OLD, SPOTLESS
REGION 8310 (N24 E11) HAS A SMALL ARCH-FILAMENT SYSTEM.   TWO OTHER
SMALL NEW SUNSPOT GROUPS HAVE EMERGED AT  S21 E03 (# 8318) AND N36 W
57 (# 8319).
IB.  SOLAR ACTIVITY FORECAST:  SOLAR ACTIVITY IS EXPECTED TO BE LOW
TO MODERATE.  REGION 8307 APPEARS LIKELY TO PRODUCE SPORADIC EVENTS.
IT APPEARS TO RETAIN THE POTENTIAL TO PRODUCE CLASS M FLARES EVERY
2-3 DAYS AND ANOTHER CLASS X OR TWO BEFORE IT REACHES THE WEST LIMB
OF THE SUN.  THE EMERGENCE OF NEW ARCH-FILAMENT SYSTEMS IN THE
SCATTERED PLAGE COVERING NEARLY 50 DEGREES IN LONGITUDE FROM 8307
INDICES THIS AREA MAY BE A SOURCE OF NEW SIGNIFICANT ACTIVE REGIONS
IN FUTURE WEEKS.
IIA.  GEOPHYSICAL ACTIVITY SUMMARY FROM 25/2100Z TO 26/2100Z:
THE GEOMAGNETIC FIELD HAS BEEN AT ACTIVE TO MINOR STORM CONDITIONS.
A SUDDEN IMPULSE WAS OBSERVED AT 26/0651 UT.  AFTER THE IMPULSE,
MID-LATITUDE K-INDICES UP TO 5 WERE OBSERVED.  ENERGETIC PARTICLE
FLUXES INCREASED IN ASSOCIATION WITH THE SUDDEN IMPULSE, WITH THE
GREATER THAN 10 MEV PROTON FLUX REACHING APPROXIMATELY 600 PFU AT
26/0330 UT.  A FORBUSH DECREASE BEGAN AT ABOUT THE TIME OF THE
SUDDEN IMPULSE AND REACHED APPROXIMATELY 10 PERCENT DECREASE BY
26/1200 UT.  THE SOLAR WIND DATA FROM THE ADVANCED COMPOSITION
EXPLORER (ACE) INDICATED A PROBABLE SHOCK PASSED THE SATELLITE
SHORTLY BEFORE THE SUDDEN IMPULSE AT EARTH.  SINCE THAT TIME, THE
SOLAR WIND VELOCITY FROM ACE HAS INCREASED TO 900 KM/S, THE DENSITY
HAS REMAINED LOWER THAN PREVIOUSLY, AND THE INTERPLANETARY MAGNETIC
FIELD DOES NOT HAVE A CLEAR PATTERN, ALTHOUGH THERE IS INDICATION
THAT THE FIELD HAS ROTATED FROM NORTH TO SOUTH TO ABOUT 10 TO 15
NANOTESLA AND THEN BACK TO VALUES THAT LEAVE IT IN THE ECLIPTIC
PLANE.
IIB.  GEOPHYSICAL ACTIVITY FORECAST:  THE GEOMAGNETIC FIELD IS
EXPECTED TO BE AT ACTIVE TO MAJOR STORM CONDITIONS.  THE PRESENT
DISTURBANCE IS EXPECTED TO CONTINUE INTO TONIGHT AND BECOME MORE
INTENSE AS CONDITIONS CHANGE IN THE SOLAR WIND AND LOCAL NIGHT-TIME
EFFECTS WORK TOGETHER TO ENHANCE K-INDICES.  VALUES AS HIGH AS 7 ARE
PROBABLE WITH A CHANCE OF HIGHER VALUES AS WELL.
III.  EVENT PROBABILITIES 27 AUG-29 AUG
CLASS M    35/35/35
CLASS X    15/15/15
PROTON     25/25/25
PCAF       GREEN
IV.  PENTICTON 10.7 CM FLUX
OBSERVED           26 AUG 127
PREDICTED   27 AUG-29 AUG  125/125/125
90 DAY MEAN        26 AUG 117
V.  GEOMAGNETIC A INDICES
OBSERVED AFR/AP 25 AUG  008/011
ESTIMATED AFR/AP 26 AUG  026/032
PREDICTED AFR/AP 27 AUG-29 AUG  060/065-025/030-010/015
VI.  GEOMAGNETIC ACTIVITY PROBABILITIES 27 AUG-29 AUG
A.  MIDDLE LATITUDES
ACTIVE                20/40/30
MINOR STORM           30/30/20
MAJOR-SEVERE STORM    40/15/05
B.  HIGH LATITUDES
ACTIVE                10/20/40
MINOR STORM           50/40/30
MAJOR-SEVERE STORM    35/25/16