Solar Terrestrial Activity Report [Image] Last update April 18, 2001 at 01:25 UT. Minor update posted at 03:15 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 17. Solar wind speed ranged between 350 and 527 km/sec. A moderate solar wind shock was observed at SOHO at 23:56 UT. Solar wind speed increased abruptly from 370 to 530 km/sec. The source of the CME is uncertain, it could be either from the X14 flare at 13:50 UT on April 15 or from a filament eruption earlier that day. Solar flare activity was moderate. Solar flux was 126.1, the planetary A index was 7 (3-hour K indices: 2322 2322, Boulder K indices: 2312 2312). Regions 9420 and 9424 were spotless early in the day, the regions have now rotated out of view. Region 9422 was quiet and stable, no spots are visible early on April 18. Region 9426 decayed slowly and was spotless early in the day. Region 9429 was quiet and stable. Region 9430 decayed slowly and was quiet. New region 9431 emerged near the southeast limb. Another region emerged to the east of region 9429 but has not yet been numbered by SEC/NOAA. Old region 9393 at and slightly behind the northeast limb is obviously still capable of producing M class flares, it is too early to tell if the region is capable of X class flaring. Comment added at 03:15 UT on April 18: Another radiation storm is in progress with a rapid increase in proton fluxes currently being observed. The source of this proton event is, according to recent LASCO C3 images, a large flare and CME in region 9415 well behind the west limb. The interplanetary magnetic field has swung strongly southwards and this could lead to severe storming at high latitudes. Flares and CMEs A total of 4 C and 1 M class events were recorded on April 16. Old region 9393 behind the northeast limb produced a long duration M1.3 event peaking at 21:57 UT. None of the C flares were optically accounted for, however, both region 9415 (behind the southwest limb) and old region 9393 were fairly active during the day and the flares likely had their origin in these regions. The background x-ray flux is at the class B5 level. Coronal holes An isolated coronal hole in the southern hemisphere was in a geoeffective position on April 15 and could cause unsettled to active conditions on April 18. An isolated coronal hole in the northern hemisphere will rotate into a possibly geoeffective position on April 19. Forecast The geomagnetic field is expected to be unsettled to major storm on April 18 and quiet to active on April 19. 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 no. Location at region numbered sunspots midnight Area Classification Comment 9420 2001.04.05 1 S07W83 0000 AXX 9422 2001.04.06 3 S13W54 0010 BXO 9424 2001.04.08 2 S15W85 0020 BXO 9426 2001.04.11 4 S08W40 0010 BXO 9428 2001.04.14 N14W78 plage 9429 2001.04.14 1 N08E23 0080 HAX 9430 2001.04.16 6 S17W46 0030 CRO 9431 2001.04.17 2 S10E49 0010 AXX Total number of sunspots: 19 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 (115.4 predicted, -0.8) 2000.11 178.8 106.5 (114.2 predicted, -1.2) 2000.12 173.6 104.5 (111.7 predicted, -2.5) 2001.01 166.6 95.7 (108.0 predicted, -3.7) 2001.02 146.6 80.1 (103.5 predicted, -4.5) 2001.03 177.7 114.2 (100.0 predicted, -3.5) 2001.04 174.3 (1) 98.5 (2) (98.8 predicted, -1.2) 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]