Solar Terrestrial Activity Report [Image] Last update April 11, 2001 at 02:20 UT. Minor update posted at 18:19 UT. [Solar and geomagnetic data - last 4 weeks (updated daily)] [Solar wind and electron fluence charts (updated daily)] [Solar cycles 21-23 (last update April 2, 2001)] [Solar cycles 1-20] [Graphical comparison of cycles 21, 22 and 23 (last update April 2, 2001)] [Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update April 2, 2001)] [Historical solar and geomagnetic data charts 1954-2000 (last update April 8, 2001)] Recent development The geomagnetic field was quiet to unsettled on April 10. Solar wind speed ranged between 505 and 602 km/sec. Solar flare activity was high. Solar flux was 169.7, the planetary A index was 9 (3-hour K indices: 3122 3322, Boulder K indices: 3022 3422). Region 9415 lost quite a bit of its areal coverage. The region is still complex and could produce further major flares. Region 9417 decayed slowly and was mostly quiet. Region 9418 decayed further and was quiet. Region 9419 reemerged with a single spot and has now rotated off the visible disk. Region 9420 was quiet and stable, as were regions 9422, 9423, 9424 and 9425. Region 9421 decayed into spotless plage. Comment added at 18:19 UT on April 11: Two solar wind shocks have been observed today. The first was a moderate shock and was recorded at SOHO at 13:02 UT with solar wind speed increasing suddenly from 500 to 620 km/sec. The source of this shock was likely a halo CME observed on April 9. A much more significant shock was observed at SOHO at 15:18 UT, this time with solar wind speed increasing from 630 to 860 km/sec over a short time span. The source of this disturbance was the large halo CME observed on April 10. Magnetometers at all latitudes displayed strong fluctuations when the CME reached Earth at 16h UT, several recorded a K index of 8 (very severe storm) or 9 (extreme storm) during the first hour of the disturbance. If the disturbance continues at its current intensity it could be possible to observe aurora in southern Europe and most of North America. The planetary A index for the 15-18h UT interval was 200. Flares and CMEs A total of 4 C and 1 X class events were observed on April 10. Region 9415 produced a major X2.3/3B flare peaking at 05:26 UT. The flare was associated with a weak type IV and a strong type II sweep, with the type II sweep indicating a shock speed of 2100 km/sec. An extremely large and fast full halo coronal mass ejection was observed in LASCO images. The CME is aimed almost directly at Earth and could cause an extreme geomagnetic storm when it impacts Earth today April 11. Region 9417 generated a C6.5 flare at 14:51 UT. April 9: Region 9415 generated a major M7.9/2B flare peaking at 15:34 UT. A strong type II sweep and a weak type IV sweep was associated with this event, as was a CME. The CME is aimed nearly directly at Earth and will impact the magnetosphere on April 11 (unless it merges with the very fast CME observed on April 10). This will likely result in minor to severe storming, very severe storming is possibly at high latitudes. The background x-ray flux is at the class B8 level. Coronal holes No obvious coronal holes are currently approaching geoeffective positions. Forecast The geomagnetic field is expected to be unsettled to extremely severe storm levels on April 11 and 12. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is very poor. Coronal holes (1) Coronal mass M and X class flares (3) ejections (2) [Coronal hole indicator][CME indicator] [M and X class flare indicator] 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 Date Actual Location region numbered no. at Area Classification Comment sunspots midnight 9412 2001.03.30 S16W65 plage 9414 2001.04.02 S23W45 plage 9415 2001.04.03 40 S23W19 0490 EKI beta-gamma-delta 9417 2001.04.03 13 S08W39 0090 DAO 9418 2001.04.04 13 N26W07 0190 DAO 9419 2001.04.04 1 N08W88 0000 AXX 9420 2001.04.05 3 S07E10 0050 CSO 9421 2001.04.06 S16W85 plage 9422 2001.04.06 2 S13E37 0050 HSX 9423 2001.04.07 2 N19W24 0010 HRX 9424 2001.04.08 2 S17E08 0020 HSX 9425 2001.04.09 4 S25W39 0030 CSO Total number of sunspots: 80 Monthly solar data Month Average solar International sunspot Smoothed sunspot flux number number 2000.01 158.1 90.1 112.9 (+1.8) 2000.02 174.1 112.9 116.8 (+3.9) 2000.03 208.2 138.5 119.9 (+3.1) 2000.04 184.2 125.5 120.8 (+0.9) cycle 23 sunspot max. 2000.05 184.9 121.6 119.0 (-1.8) 2000.06 179.8 124.9 118.7 (-0.3) 2000.07 202.3 170.1 119.8 (+1.1) 2000.08 163.0 130.5 118.6 (-1.2) 2000.09 182.1 109.7 116.2 (-2.4) 2000.10 167.4 100.1 (114.6 predicted, -1.6) 2000.11 178.8 106.5 (112.6 predicted, -2.0) 2000.12 173.6 104.5 (110.1 predicted, -2.5) 2001.01 166.6 95.7 (106.3 predicted, -3.8) 2001.02 146.6 80.1 (101.9 predicted, -4.4) 2001.03 177.7 114.2 (98.4 predicted, -3.5) 2001.04 199.6 (1) 67.8 (2) (97.1 predicted, -1.3) 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. ------------------------------------------------------------------------ Do you know about the survey which will be held this Summer among the listeners of WWV and WWVH? There is information about this survey at 16 minutes past the hour on WWV and at 47 minutes past the hour on WWVH. If you want to participate send an email with your name and address. ------------------------------------------------------------------------ [DX-Listeners' Club] [DX News] [StudyWeb]