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91-10-26.DLY
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1991-10-27
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DAILY SUMMARY OF SOLAR GEOPHYSICAL ACTIVITY
26 OCTOBER, 1991
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
(Based In-Part On SESC Observational Data)
SOLAR AND GEOPHYSICAL ACTIVITY INDICES FOR 26 OCTOBER
-----------------------------------------------------
!!BEGIN!! (1.0) S.T.D. Solar Geophysical Data Broadcast for DAY 299, 10/26/91
10.7 FLUX=251 90-AVG=195 SSN=270 BKI=3353 4343 BAI=022
BGND-XRAY=C2.6 FLU1=*.*E*** FLU10=7.1E+03 PKI=4354 4434 PAI=028
BOU-DEV=020,023,077,032,064,038,053,031 DEV-AVG=039 NT SWF=05:367
XRAY-MAX= X1.6 @ 2047UT XRAY-MIN= C2.0 @ 1111UT XRAY-AVG= M1.2
NEUTN-MAX= +001% @ 2125UT NEUTN-MIN= -002% @ 2345UT NEUTN-AVG= -0.3%
PCA-MAX= +0.2DB @ 1950UT PCA-MIN= -0.3DB @ 2220UT PCA-AVG= -0.0DB
BOUTF-MAX=55307NT @ 2326UT BOUTF-MIN=55267NT @ 2100UT BOUTF-AVG=55290NT
GOES7-MAX=E:+118NT@ 0630UT GOES7-MIN=N:-030NT@ 0900UT G7-AVG=+064,+054,+002
GOES6-MAX=P:+123NT@ 2230UT GOES6-MIN=E:-050NT@ 0630UT G6-AVG=+073,+001,+019
FLUXFCST=STD:260,265,265;SESC:260,265,265 BAI/PAI-FCST=020,015,015/024,020,015
KFCST=2234 3444 3345 4333 27DAY-AP=023,046 27DAY-KP=3444 4433 3454 3366
WARNINGS=*MAJFLR;*PROTFLR;*PROTON;*PCA;*GSTRM;*AURMIDWRN
ALERTS=**MAJFLR:X1.6/2B,S11E20(6891),1846-2047-2243,II=2@2049,IV=2@2052;
**MINFLR:M1.1@0015;**SWEEP:IV=2@0041;**MINFLR:M1.2@1301;
**MAGSI:43NT@0635
!!END-DATA!!
BRIEF SUMMARY OF EVENTS
-----------------------
Solar Region 6891 (S20E21) released an enormous amount of energy today
in the form of long-duration minor flares and a significant major flare. The
largest event of the day began as a minor class M1 flare which was sustained
at the M1 level for an abnormal length of time (two hours) before the second
increase in x-rays began. This second burst began near 20:20 UT and quickly
became a major category flare. X-rays peaked at a class X1.6 level at 20:47
UT. This peak was sustained for many minutes before beginning a slow
decline. The post-maximum x-ray profile follows:
Maximum Class X1.6: 20:47 UT
Fell below X1.0: 21:11 UT
Fell below M5.0: 21:45 UT
X-rays never dropped below the M1.0 level until several hours later due to
other minor M-class activity.
Moderate intensity Type II and IV sweeps were observed from this flare.
The Type IV began at 20:52 UT and ended several hours later at 23:42 UT
(preliminary). A tenflare was observed at 20:30 UT, reaching a peak
intensity of 1,200 sfu. The duration of the tenflare was 34 minutes.
This flare is thought to have ejected protons. Although no protons have
yet been observed, there is a moderate probability that protons may arrive
after 04:00 UT on 27 October. Models indicate a possible peak flux of 200
pfu at greater than 10 MeV. If this holds true, a PCA event will
materialize.
Region 6891 experienced considerable fragmentation of its large leader
penumbra over the last 24 hours. Nevertheless, this region is exceptionally
large, very complex, and very potent. Despite these structural changes,
there are no signs that the level of flaring evident in this region will
drop. Minor to major solar flares are still anticipated from this region
over the next 24 to 72 hours. There is a high risk for terrestrial impacts
from future major energetic events. Class M, X, and associated proton
ejections are also a high probability.
Two new regions were assigned today. Region 6895 (N24W31) and 6896
(S03E63).
The geomagnetic field has been mostly active over the last 24 hours. A
sudden magnetic impulse of 43 gammas was observed at 06:35 UT. The source is
not clearly known. Conditions over the next 24 hours should continue mostly
active with possible periods of minor storming over the high and some middle
latitude regions. Activity may be substantially enhanced late in the UT day
of 28 October or early on 29 October when an interplanetary shockwave from
todays X1.6/2B tenflare is expected to arrive. The level of activity which
may be observed is unknown at the present time. Estimates of minor to
possibly major storming are suspected. A more definitive forecast will be
presented later this UT day.
Auroral activity has become somewhat enhanced over the last 24 hours.
Conditions should be mostly moderate over the high latitude regions, with
possible sporadic and isolated periods of high activity over some of these
regions. By 29 October, effects from todays major flare may produce a
prodigious increase in auroral storm activity, depending on how severe the
impact of the disturbance becomes. At the present time, auroral activity is
forecasted to become moderate to high over the middle latitude region.
Equatorward expansion of the auroral oval is almost a certainty if this
disturbance materializes. There will also be a slight chance for low
latitude observations of auroral activity during the moonless hours of the
evening. Lunar phase should not be a significant inhibitor. A more
definitive forecast will be made available later this UT day.
HF propagation conditions were normal, becoming below normal today.
Significant levels of noise and increased anomalous absorption was observed
over the sunlit sectors in response to the significant periods of strongly
enhanced x-rays. As is evident in the SWF statistic above, the estimated
maximum number of minutes during the daylight hours where HF radio signals
may have been degraded was 367 minutes, or over six hours. Actual
observations indicate the daytime signal degradations were similar to this
number, although during much of the time the signals were not strongly
affected. In some instances, enhancements were observed. This was
particularly true with signals near or above 30 MHz. A major SID/SWF was
observed in conjunction with the main x-ray burst of the major X1.6 flare.
Frequencies below approximately 12 MHz were almost entirely absorbed.
Effects were less pronounced on frequencies above 15 MHz. Near blackout
conditions existed for approximately 30 to 45 minutes on the lower bands
below 10 MHz. Conditions should continue unstable over the next 24 hours as
a result of transient solar flaring and possible periods of major flaring.
A further decrease in propagation conditions associated with the
interplanetary disturbance presently thought to be in transit is anticipated
for 29 and 30 October. Additional major solar flares could prolong the
period of disturbed conditions. A more definitive forecast will be presented
later this UT day.
Please note that the forecast K and A-index values given in todays
data set were generated prior to the assessment of todays major energetic
activity and will therefore not be entirely correct. In particular, the 48
and 72 hour forecasts are the most inaccurate and will be adjusted tommorrow.
** End of Daily Update **