Solar Terrestrial Activity ReportSolar Terrestrial Activity Report

Last update September 25, 2001 at 05:10 UTC. Minor update posted at 06:10 UTC.
[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update September 1, 2001)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 1, 2001)]
[Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update September 1, 
2001)]
[Historical solar and geomagnetic data charts 1954-2001 (last update July 27, 
2001)]
Recent development
The geomagnetic field was quiet to unsettled on September 24. Solar wind speed 
ranged between 357 and 500 km/sec.
Solar flare activity was high. Solar flux was 279.3 (new high for solar cycle 
23. The average for the month could exceed 230, more than 10% above the previous 
high), the planetary A index was 6 (3-hour K indices: 3112 2221, Boulder K 
indices: 3221 2221). Region 9616 rotated off the visible disk. Region 9620 
decayed slowly and quietly. Region 9621 was mostly unchanged and quiet. Region 
9622 decayed slowly and quietly. Region 9624 was quiet and stable. Region 9627 
developed slowly and was quiet. Region 9628 developed slowly and has 3 magnetic 
deltas. A major flare is possible. Region 9629 was mostly unchanged and quiet. 
Region 9631 decayed and was spotless by the end of the day. Region 9632 
developed slowly and has a large penumbra containing a magnetic delta. The 
region could produce further major proton flares. Region 9633 was quiet and 
stable. Region 9634 was quiet and stable. Region 9635 developed slowly and was 
mostly quiet. New region 9636 was split off from region 9634 at the northeast 
limb. New region 9637 rotated into view at the southeast limb.
Comment added at 06:10 UTC on September 25: A major M7.6 flare was observed at 
04:40 UTC and was associated with a type II radio sweep and a likely CME. 
Further details on this event will be posted later today. Region 9628 produced 
an M2.0 flare peaking at 05:20 UTC.
The above 10 MeV proton flux has reached the 2200 pfu level.
Flares and CMEs
A total of 7 C and 1 X class events were observed on September 24. Region 9628 
produced a C2.6 flare at 00:35 and a C2.8 flare at 06:13 UTC. Region 9635 
generated a C2.7 flare at 08:12 UTC. Region 9632 was the source of a major long 
duration X2.6/2B proton event peaking at 10:38 UTC. A long lasting weak type IV 
radio sweep was recorded as well. A large and fast full halo CME was observed in 
LASCO C3 images. The CME will impact Earth sometime between late today and noon 
on September 26 and will likely cause major to severe geomagnetic storming. 
Above 10 and 100 MeV proton events started soon after the flare, both are still 
intensifying slowly and will likely continue to do so until the CME impacts 
Earth. So far the above 10 MeV proton flux has reached 1800 pfu while the above 
100 MeV flux has reached 22 pfu. A strong polar cap absorption event is in 
progress.
The background x-ray flux is at the class C2 level.
Coronal holes
No obvious coronal holes are currently approaching geoeffective positions.
Forecast
The geomagnetic field is expected to be quiet to unsettled until the arrival of 
the CME from the X2 flare described above. When the CME impacts the 
magnetosphere a major to severe disturbance will likely begin. This disturbance 
could last well into September 27. Long distance medium wave (AM) band 
propagation along east-west paths over high and upper middle latitudes is 
useless.
      Coronal holes (1)Coronal mass ejections (2)M and X class flares (3)


1) Effects from a coronal hole could reach earth within the next 5 days.
2) Material from a CME is likely to impact earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 
hours.
Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.
Active solar regions (Recent map)
      Solar regionDate numberedActual no. sunspotsLocation at 
      midnightAreaClassificationComment
      96162001.09.112S09W880060CSO 
      96172001.09.12 N10W86  plage
      96202001.09.165N12W360080CSO 
      96212001.09.167N14W320210CAO 
      96222001.09.1715N13W590270EAO 
      96232001.09.17 N21W48   
      96242001.09.171N03W260100HSX 
      96262001.09.18 N25W40  plage
      96272001.09.1816N01W110080DSO 
      96282001.09.1866S18W010880FKCbeta-gamma-delta
      96292001.09.195N26W280040CSO 
      96302001.09.20 N27W88  plage
      96312001.09.201N08W690000AXX 
      96322001.09.2023S19E190790DKIbeta-gamma-delta
      96332001.09.221N22E500090HAX 
      96342001.09.225N12E540120DAO 
      96352001.09.238N21E020040DSO 
      96362001.09.247N12E650260EAO 
      96372001.09.243S14E710140DAO 
      Total number of sunspots:165 

Monthly solar data
      MonthAverage solar fluxInternational sunspot numberSmoothed sunspot number
      2000.03208.2138.5119.9
      2000.04184.2125.5120.8
      cycle 23 sunspot max. 
      2000.07202.3170.1119.7
      2000.08163.0130.5118.6 (-1.1)
      2000.09182.1109.7116.3 (-2.3)
      2000.10167.499.4114.5 (-1.8)
      2000.11178.8106.8112.8 (-1.7)
      2000.12173.6104.4112.1 (-0.7)
      2001.01166.695.6108.8 (-3.3)
      2001.02146.680.6104.1 (-4.7)
      2001.03177.7113.5(104.5 predicted, +0.4)
      2001.04177.7108.2(106.0 predicted, +1.5)
      2001.05147.197.3(105.5 predicted, -0.5)
      2001.06173.0134.0(103.8 predicted, -1.7)
      2001.07131.382.2(102.5 predicted, -1.3)
      2001.08162.9106.8(103.1 predicted, +0.6)
      2001.09226.2 (1)176.7 (2)(102.5 predicted, -0.6)

1) Running average based on the daily 20:00 UT solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (SEC/NOAA) sunspot number. 
The official international sunspot number is typically 25-40% less.
This report has been prepared by Jan Alvestad. It is based partly on my own 
observations and interpretations, and partly on data from sources noted in solar 
links. Comments and suggestions are always welcome.


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