Solar Terrestrial Activity ReportSolar Terrestrial Activity Report

Last update September 26, 2001 at 04:00 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 major storm on September 25. Solar wind speed 
ranged between 352 and 800 km/sec. A strong solar wind shock was observed at 
19:57 UTC at SOHO with solar wind speed abruptly increasing from 390 to 800 
km/sec. The source of the shock was the full halo CME observed after the X2 
flare just over 34 hours earlier. The above 10 MeV proton flux peaked near 10000 
pfu shortly after the arrival of the CME. Although the shock was strong the 
interplanetary magnetic field has been fairly confused since then and the 
geomagnetic disturbance has been less intense than expected.
Solar flare activity was high. Solar flux was 275.1, the planetary A index was 
18 (3-hour K indices: 1221 1256, Boulder K indices: 1221 1146). Region 9620 
decayed slowly and quietly, as did region 9621. Region 9622 decayed quickly and 
was quiet, the region is about to rotate off the visible disk. Regions 9624 and 
9627 were quiet and stable. Region 9628 developed slowly in the central and 
trailing spot groups and still has a couple of magnetic delta configurations. 
Another major flare is possible. Region 9629 decayed and could become spotless 
today. Region 9631 was spotless in all available images. Region 9632 was mostly 
unchanged and could produce major flares. Region 9633 was quiet and stable, as 
was region 9634. Region 9635 developed slowly and was quiet. Region 9636 
developed slowly and has a weak magnetic delta within the main penumbra. Minor M 
class flares are possible. Region 9637 was quiet and stable. New region 9638 
emerged near the northeast limb.
Flares and CMEs
A total of 3 C and 4 M class events were observed on September 25. Region 9628 
produced an M1.1 flare at 01:48, a major M7.6/1N flare at 04:40 (with an 
associated moderate type II sweep and likely a geoeffective CME which could 
arrive on September 27), an M1.8 flare at 05:20, an M2.0 flare at 10:27 (with an 
associated weak type II radio sweep), a C7.0 flare at 17:17, a C2.5 flare at 
18:53 and a C4.2 flare at 20:27 UTC.
The background x-ray flux is at the class C2 level.
Coronal holes
A weak coronal hole is located east of region 9635 and will be in a geoeffective 
position on September 26. Any effects from this coronal hole on the geomagnetic 
field are uncertain. The associated coronal stream could arrive on September 29.
Forecast
The geomagnetic field is expected to be active to major storm on September 
26-27. Long distance medium wave (AM) band propagation along east-west paths 
over high and upper middle latitudes is very poor to 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
      96202001.09.162N12W500070HSX 
      96212001.09.164N14W450150CAO 
      96222001.09.176N13W730200DAO 
      96232001.09.17 N21W61   
      96242001.09.171N03W400090HSX 
      96262001.09.18 N25W53  plage
      96272001.09.1816N01W240060DAO 
      96282001.09.1866S18W140880FKCgamma-delta
      96292001.09.192N26W420000BXO 
      96312001.09.201N09W850000AXX 
      96322001.09.2023S19E060700DKIbeta-gamma-delta
      96332001.09.221N22E360070HSX 
      96342001.09.2211N12E410080DAO 
      96352001.09.2313N21W120050DSO 
      96362001.09.2417N13E540300CKObeta-gamma-delta
      96372001.09.245S15E590180DAO 
      96382001.09.252N03E610030HSX 
      Total number of sunspots:170 

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(105.7 predicted, +1.6)
      2001.04177.7108.2(108.8 predicted, +3.1)
      2001.05147.197.3(108.0 predicted, -0.5)
      2001.06173.0134.0(106.3 predicted, -1.7)
      2001.07131.382.2(105.0 predicted, -1.3)
      2001.08162.9106.8(105.6 predicted, +0.6)
      2001.09228.1 (1)187.3 (2)(105.0 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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