:Product: Weekly Highlights and Forecasts :Issued: 2001 Sep 26 2112 UT Highlights of Solar and Geomagnetic Activity 17 - 23 September 2001 Solar activity reached high levels for the third consecutive week. The period began with activity at high levels due to an M8/1n flare at 17/1550 UTC from Region 9608 (S27, L = 109, Fkc/1110 on 10 September). Region 9608 was large, magnetically complex, and in a gradual decay phase at the time of the flare. This region also produced isolated low-level M-class flares until it rotated out of view on 18 September. Activity varied from low to moderate levels during the rest of the period due to isolated C- and M-class flares from a number of active regions (for flare specifics, please refer to the Energetic Events and Optical Flares lists). Active regions of note included Region 9628 (S18, L = 293, class/area Fkc/800 on 20 September) and Region 9632 (S18, L = 273, class/area Dki/780 on 23 September). Both regions were large and magnetically complex with magnetic delta configurations within their trailer spots. Both regions produced isolated C- and M-class flares during the period. Region 9628 appeared to be the return of old 9591, which had a history of major flare production. (Note: Regions 9628 and 9632 each produced a major flare after the close of the highlights period. Details will be provided in next week's issue.) Solar Wind data were available from the NASA Advanced Composition Explorer (ACE) spacecraft for most of the period. A weak coronal transient passed the spacecraft beginning around midday on 18 September. This brief passage was characterized by relatively modest increases in total IMF field intensity and density and a southward turn of IMF Bz during 18/1600 - 1800 UTC with maximum deflections to minus 12 nT (GSM). IMF Bz turned mostly southward during 22/0800 - 1800 UTC with maximum deflections to minus 07 nT. A CME-related shock passed ACE on 23 September at approximately 0800 UTC. The passage was associated with abrupt increases in density and total IMF field intensity, along with a more gradual increase in velocities which (briefly) peaked near 620 km/sec. In addition, IMF Bz turned southward during 23/1300 - 1900 UTC with maximum deflections to minus 11nT observed around 23/1700 UTC. There were no proton events during the period. (Note: a proton event began on 24 September following a major flare from Region 9632. Details will be provided in next week's issue.) The greater than 2 MeV electron flux at geosynchronous orbit was at normal levels during most of the period. The geomagnetic field was largely undisturbed during 17 - 21 September, the exception being a brief active period on 18 September associated with the weak coronal transient mentioned above. Active to minor storm periods occurred on 22 September associated with the sustained period of southward IMF Bz described above. The most significant disturbance of the period occurred on 23 September due to the CME passage described above. Active to minor storm conditions occurred globally during this disturbance with major to severe storm periods at high latitudes. Forecast of Solar and Geomagnetic Activity 26 September - 22 October 2001 Solar activity is expected to be at low to high levels. Isolated M-class flares are expected. There will be a fair chance for isolated major flare activity during the period. A proton event began on 24 September and was in progress at the time of this report. This proton event is expected to continue for the next few days. There will be a chance for another proton flare during the period. The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at normal to moderate levels during most of the period. A major geomagnetic storm is expected during 25 - 26 in the wake of an X-class flare and accompanying halo CME on 24 September. Active to severe storm levels will be possible during this storm, which is expected to begin early on 26 September. Active periods will be possible during 12 October due to coronal hole effects. Quiet to unsettled conditions are expected during the remainder of the period. .