:Product: Weekly Highlights and Forecasts :Issued: 2001 Oct 23 2112 UT Highlights of Solar and Geomagnetic Activity 15 - 21 October 2001 Solar activity ranged from low to high levels. Activity reached high levels on 19 October due to three major solar flares. Activity was mostly low through 18 October with isolated C-class flares, but increased to moderate levels on 17 October due to an isolated M-class flare from Region 9658 (S14, L = 024, class/area Fao/230 on 19 October) (for flare details, please refer to the Energetic Events and Flares lists). Region 9658 was moderate in size and magnetic complexity, but in a gradual decay phase during 15 - 16 October. However, the region showed increased magnetic complexity on 17 October to include a short-lived magnetic delta configuration within its trailer spots. It appeared to stabilize on 18 October, but remained moderately complex. It began to gradually decay on 20 October and was crossing the west limb as the period ended. Activity rose to high levels on 19 October due to three major flares from Regions 9658 and 9661 (N15, L = 357, Ekc/800 on 16 October). The first was an X1/2b at 19/0105 UTC from Region 9661 associated with a 1400 sfu Tenflare, Type II and IV radio sweeps, and an Earth-directed coronal mass ejection (CME). Region 9661 also produced an X1/2b at 19/1630 UTC associated with a 950 sfu Tenflare, Type II and IV radio sweeps, a loop-prominence system and a Earth-directed CME. Region 9658 was responsible for the third major flare of the day: an M5/1b at 19/0943 UTC associated with a 370 sfu Tenflare. Region 9661 gradually developed through 17 October, then appeared to stabilize on 18 October as a large, magnetically complex spot group with strong magnetic field gradients and a magnetic delta configuration within the trailer portion of the region. Activity decreased to low levels on 20 October as Regions 9658 and 9661 began to gradually decay. Activity became moderate on 21 October due to an M2/2n flare from Region 9661, which remained in a gradual decay phase. Another sunspot group of interest was Region 9672 (S20, L = 269, Dko/330 on 21 October), which produced isolated C-class subflares as it gradually developed. Note: Region 9672 produced two major flares on 22 October; details will be provided in next week's report. Solar Wind data were available from the NASA Advanced Composition Explorer (ACE) spacecraft for most of the period. A weak transient disturbance was observed early on 15 October associated with relatively minor variations in velocity and density, and mostly southward IMF Bz early in the day. A CME front passed the spacecraft at approximately 21/1614 UTC. Strong increases in total IMF field intensity, proton temperature, and velocities (peaks as high as 730 km/sec) accompanied the passage, along with a strong southward turn of IMF Bz with peak deflections to minus 23 nT (GSM). This passage was in progress as the period ended. The source for this CME was likely the X1/2b flare at 19/0105 UTC from Region 9661. A greater than 10 MeV proton flux event at geosynchronous orbit began at 19/2255 UTC in the wake of major flare activity earlier that day. The event peaked at 11 pfu at 19/2235 UTC, then ended at 19/2255 UTC. The greater than 100 MeV proton flux became enhanced in the wake of the major flares, but did not reach event criteria. The greater than 2 MeV electron flux at geosynchronous orbit ranged from normal to moderate levels. The geomagnetic field was mildly disturbed early on 15 October with unsettled to active levels due to a weak coronal transient. A CME-related geomagnetic storm occurred on 21 October (and continued into 22 October). The disturbance began with a sudden impulse at 21/1645 UTC (15 nT, as measured by the Boulder USGS magnetometer) followed by minor to severe storm levels. Forecast of Solar and Geomagnetic Activity 24 October - 19 November 2001 Solar activity is expected to range from low to high levels. Isolated, low-level M-class flares are expected throughout the period. Region 9672 is likely to produce another major flare before it rotates out of view on 30 October. There will be an increased chance for isolated major flare activity during the latter half of the period with the return of old Regions 9658 and 9661. There will be a fair chance for a proton event from Region 9672 until it departs the disk on 30 October. There will be a slight chance for a proton flare during the latter half of the period with the return of old Regions 9658 and 9661. The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at normal to moderate levels during most of the period. However, high flux levels will be possible around 26 - 30 October and 06 - 07 November. Geomagnetic storm conditions are expected during 24 - 25 October due to an anticipated CME passage. Active to major storm levels will be possible during this passage. Active conditions will be possible during 26 - 28 October and 04 - 05 November. Quiet to unsettled conditions are expected during the remainder of the period. .