HELIOS no. 54        01.November 1998

This Helios Newsletter continues a series newsletters under the same name as above and that were issued as the newsletter of the Solar Section of the Norwegian Astronomical Society.  Helios no. 1 was issued on 2nd May 1979 and ended almost simultaneously as I resigned as the leader of that section, i.e. in August 1989.   Now I bring it to life again, started where I left it. 
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Here is the first Report from Cycle 23:

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SWO PRF 1200 01 September 1998
SWO PRF 1200
01 Sep 1998
Space Weather Highlights
24-30 Aug 1998
Solar activity rose to high levels during the period. Region 8307 (N31, L = 038, class/area Dko/570 on 22August) produced a long-duration X1/3B flare at 24/2212UT accompanied by a 2100 s.f.u. Tenflare, Types II and IV radio sweeps and a loop prominence system. Activity dropped to very low to low levels during 25 - 29August, during which time Region 8307 gradually simplified and produced occasional C-class subflares. Region 8319 (N19, L = 008, class/area Eki/570 on 30 August) grew at a rapid pace during 30 August and produced two impulsive M-class flares, an M1/1N at 30/0541UT and an M1/1N at 30/0937UT, neither of which were impressive in radio output. Old Region 8293 rotated into view on 30 August and was numbered as new Region 8323 (S22, L = 273, class/area Ekc/780 on 30 August). This region was large with a compact sunspot distribution and moderate magnetic complexity and produced several C-class flares. The August (provisional) Brussels S.I.D.C. sunspot number was 91.7, the highest seen so far this cycle and the highest since November of1992.
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SWO PRF 1201 08 September 1998
SWO PRF 1201
08 Sep 1998
Space Weather Highlights
31 Aug – 06 Sep 1998
Solar activity declined to moderate levels during the period. Region 8307 (N31, L = 038, class/area
Dko/570 on 22 August) produced an impulsive M1/SF flare at 31/1539UT with Types II and IV
radio sweeps and moderate discrete frequency bursts in the 245 - 606 MHz range. It also produced
an impulsive M1/1F at 01/0459UT with weak radio emission. This region was in gradual decline as it
crossed the west limb on 02 September. Region 8319 (N19, L = 010, class/area Eko/740 on 31
August) produced an M2/SF flare at 02/1707UT associated with minor radio emission. Region 8319
had stabilized as a large, structurally simple spot group a day prior to the M-flare and remained stable
for the rest of its time on the visible disk. Region 8323 (S22, L = 271, class/area Fkc/1460 on 03
September) also produced an M1/SF flare at 03/1608UT and a C3/SF at 03/1430UT associated
with Types II and IV sweeps and minor discrete radio emissions. This region was generally stable
through the period despite its large size and magnetic complexity. An M1 X-ray flare occurred at
03/0421UT and was optically tied (via YOHKOH SXT observations) to Region 8326 (N20, L =
196, class/area Eso/160 on 04 September), which was beginning to rotate into view at the time of the
flare. Region 8326 remained stable for the rest of the period.
***
SWO PRF 1202 15 September 1998
SWO PRF 1202
15 Sep 1998
Space Weather Highlights
07-13 September 1998
Solar activity was at low to moderate levels with two M-class flares detected. Region 8323 (S22,
L = 271, class/area Fkc/1460 on 03 September) was the probable source of an M2 x-ray flare that
occurred at 09/0458UT. This flare was accompanied by major Types II and IV radio sweeps and a
310 SFU Tenflare. Region 8323 slowly decayed during the period before crossing the west limb on
10 September. Region 8333 (N12, L = 222, class/area Dao/230 on 12 September) produced an
M2/1B at 11/1603UT. Isolated C-class flares from a variety of regions occurred during the remaining
days.
Real-time solar wind data were available from the Advanced Composition Explorer (ACE)
spacecraft during most of the period. Velocities were in the 300 - 400 km/sec range through 11
September, then increased to a range of 330 - 530 km/sec for the rest of the period. Densities ranged
from 02 - 15 p/cc. Bz was northerly through 11 September, then became southerly for most of the
rest of the period with maximum deflections of minus 09 nT (GSM) detected on 12 September. Solar
sector orientation was mostly away (phi angle near 135 degrees) during 10 - 11 September, but was
not discernible during the remaining days.
***
SWO PRF 1203 22 September 1998
SWO PRF 1203
22 Sep 1998
Space Weather Highlights
14-20 September 1998
Solar activity was at very low to moderate levels. Isolated B- and C-class subflares occurred during 14
- 19 September. Activity rose to moderate levels on 20 September by virtue of an M1 flare at20/0251UT with an associated major Type IV radio sweep. Radio heliograph images indicated that Region 8340 (N20, L = 012,class/area Dko/490 on 20 September) was the source of the flare. This region was the return of old Region8319 which produced five M-class flares during its previous passage. Old Region 8307, which produced six major flares during 17 - 24 August, returned on 15September as a simple plage region.
***SWO PRF 1204
29 September 1998
SWO PRF 1204
29 Sep 1998
Space Weather Highlights
21-27 September 1998
Solar activity was low during most days, but rose to high levels on 23 September. Region 8340 (N20,
L = 013, class/area Dko/540 on 21 September) produced an M6/3B flare at 23/0713UT following a period of slow growth. Major Types II and IV radio sweeps and strong discrete radio emission accompanied the flare. Slow growth continued in Region 8340 following the flare and by 24 September a delta magnetic configuration had formed. Region 8344 (S20, L = 001, class/area Dso/070 on 24 September) also developed a delta magnetic configuration on 24 September following a day of gradual growth. Both regions slowly declined during the remainder of the period and produced isolated B- and C-class flares with minor radio emission. Real-time solar wind data were available from the Advanced Composition Explorer (ACE) spacecraft during most of the period. An interplanetary shock front (produced by the M6/3B flare) was detected by ACE around 24/2300UT. Bz became strongly southward following the shock with a maximum deflection of minus 27 nT (GSM) detected at 24/2333UT. Bz remained southward until around 25/1800UT. Thereafter, Bz hovered around zero and ranged from plus 07 to minus 07 nT. A greater than 10 MeV proton enhancement began around 23/1300UT following the M6/3B flare, then increased to event levels beginning 25/0010UT. The event peaked at 44 PFU at 25/0130UT and ended at 25/0230UT. Polar cap absorption associated with the proton event peaked at 1.5 dB at05/0103UT. The greater than 2 MeV electron flux at geosynchronous altitude was at normal to moderate levels through 24 September, then increased to moderate to high levels for the balance of the period.
A geomagnetic storm occurred during 25 September in response to the M6/3B flare. Severe storm levels were detected at all latitudes during the disturbance. The field declined to mostly quiet to unsettled levels after 25/1800UT and remained so for the rest of the period although brief storm intervals were detected at high latitudes. A Forbush decrease of minus 15 percent was detected by the Thule neutron monitor during the storm.
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SWO PRF 1205 06 October 1998
SWO PRF 1205
06 Oct 1998
Space Weather Highlights
28 September – 04 October 1998
Solar activity ranged from very low to moderate during the period. Two M-class flares occurred. The first was an optically uncorrelated M3 at 28/0654UT with major Types II and IV radio sweeps.
Region 8340 (N20, L = 013, class/area Dko/540 on 21 September) produced the second, a long-duration M2/2N at 30/1350UT with associated major Types II and IV radio sweeps, a 450 SFU Tenflare, and a loop prominence system. Region 8340 was crossing the west limb at the time of the flare and had been in a period of slow decay since 25 September. Isolated B- and C-class subflares were observed from a few small regions during the remaining days of the period. Real-time solar wind data were available from the Advanced Composition Explorer (ACE) spacecraft during most of the period. Significant wind variations were detected during the geomagnetic disturbance discussed below. Solar wind velocities increased from 440 - 600 km/sec on 01 October, followed by an increase to 720 km/sec on 02 October. Densities peaked at 11 p/cc. Bz reached maximum southerly deflections of minus 10 dB during the disturbance. Solar sector orientation was away (phi angle near 135 degrees) through 29 September, but was not discernible during the rest of the period.
A solar proton event (SPE) followed the long-duration M2/2N of 30 September. The greater than 100 MeV SPE began at 30/1440UT, reached a maximum of 3.0 PFU at 30/1920UT, and ended at 30/2235UT. The greater than 10 MeV SPE began at 30/1520UT, reached a maximum of 1200 PFU at 01/0025UT, and ended at 02/0830UT. The polar cap absorption event associated with the SPE peaked at 4.9 dB (as measured by the Thule 30 mHz riometer) at 30/2125UT, then ended around 02/0300UT. The greater than 2 MeV electron flux at geosynchronous altitude was at moderate to high levels during the entire period.
***
SWO PRF 1206 13 October 1998
SWO PRF 1206
13 Oct 1998
Space Weather Highlights
05 - 11 October 1998
Solar activity ranged from very low to moderate during the period. Region 8355 (S22, L = 123,class/area Dai/220 on 08 October) produced two low-level M-class flares on 07 October during a brief period of rapid development. The first was an M1/1N at 07/1247UT and the second was an M2/SF at 07/1712UT. Neither flare was impressive in radio aspects. Region 8355 stabilized as a small, simple bipole the following day, then produced isolated B- and C-class subflares during the rest of the period. Another flare of note was an optically uncorrelated C4 at 08/0837UT accompanied by a major Type II radio sweep and minor discrete radio emission.Real-time solar wind data were available from the Advanced Composition Explorer (ACE) spacecraftduring most of the period. Significant solar wind discontinuities were detected during the geomagnetic disturbance discussed below. Solar wind velocities increased from 340 - 620 km/sec on 07 October followed by a gradual decrease to 370 km/sec by the end of the period. Densities were in the 02 – 04 range during most of the period, but increased during 06 - 07 October with a peak of 40 p/cc detected on 06 October. Bz became mostly south during 07 - 09 October with maximum southerly deflections of minus 12 nT (GSM) on 07 October. Solar sector orientation was not discernible through 06 October, then became away (phi angle near 135 degrees) for the balance of the period. There were no significant proton enhancements detected at geosynchronous altitude. The greater than 2 MeV electron flux at geosynchronous altitude was at moderate to high levels during the entire period.
***
SWO PRF 1207 20 October 1998
SWO PRF 1207
20 Oct 1998
Space Weather Highlights
12-18 October 1998
Solar activity ranged from low to moderate during the period. Region 8358 (N15, L = 104, class/area Dao/290 on 18 October) grew gradually during the period and produced an M2/1N flare at 18/0145UT associated with minor radio emission. This region stabilized following the M-flare. Isolated B- and C-class flares occurred during the rest of the period. A 27 degree filament, last observed near N19E10, disappeared from the disk on 15 October. An Earth-directed coronal mass ejection (CME) was associated with the filament disappearance.Real-time solar wind data were available from the Advanced Composition Explorer (ACE) spacecraft during most of the period. An interplanetary shock passage was detected at 18/1902UT associated with the CME described above. Velocities increased from 310 - 400 km/sec, densities increased to 48 p/cc, and Bz became southerly at minus 08 nT immediately following the passage. Note: more extreme Bz and density variations occurred on 19 October associated with the CME passage There were no significant proton enhancements detected at geosynchronous altitude during the summary period. However, interplanetary shock-accelerated particles caused a >10 MeV proton enhancement on 19 October. The enhancement will be described in next week's PRF. The greater than 2 MeV electron flux at geosynchronous altitude was at moderate to high levels through 15 October, then declined to normal to moderate levels for the balance of the period. The geomagnetic field was at quiet to unsettled levels throughout the period. Note: a geomagnetic storm occurred on 19 October following the CME mentioned above.
***
SWO PRF 1208 27 October 1998
SWO PRF 1208
27 Oct 1998
Space Weather Highlights
19-25 October 1998
Solar activity was low throughout the period. Isolated C-class subflares occurred each day. A long-duration C7 x-ray flare occurred at 20/2103UT and was associated with a weak Type IV radio sweep and minor discrete radio emission. Region 8365 (S27, L = 031, class/area Eko/330 on 23 October) grew rapidly during 21 - 22 October and produced C-class subflares, none of which were associated with significant radio emission. By 23 October, Region 8365 had stabilized as a moderate-sized spot group. It remained stable for the rest of the period and produced isolated B- and C-class subflares. Real-time solar wind data were available from the Advanced Composition Explorer (ACE) spacecraft during most of the period. The spacecraft detected an interplanetary shock passage at 18/1902UT related to a halo-CME produced by a large filament disappearance on 15 October. Early on 19 October, following the shock, densities increased to a peak of 64 p/cc and Bz became strongly southward with maximum deflections of minus 21 nT (GSM). By late 19 October Bz returned to near zero, then ranged from plus 08 nT to minus 05 nT for the rest of the period. Coronal hole effects were evident during 20 - 24 October with increased solar wind speeds (maximum 740 km/sec on 22 October) and low densities (01 - 04 p/cc). A greater than 10 MeV proton enhancement at geosynchronous altitude occurred on 19 October and was related to the shock passage described above. Fluxes returned to background levels by 21 October. The greater than 2 MeV electron flux at geosynchronous altitude increased to high levels on 21October and remained so for the balance of the period. The geomagnetic field was at minor to severe storm levels on 19 October following the CME-related shock passage described above with severe storm levels limited to high latitudes. Field activity declined to unsettled to active levels by late 19 October. A high-speed coronal hole wind stream disturbed the field during 20 - 24 October with occasional, brief active periods at middle latitudes and active to minor storm periods at high latitudes. Field activity declined to quiet to unsettled levels for the rest of the period.

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Helios no. 55 will be issued 01. February 1999

CV-Helios Network 01.Nov.98