:Product: Weekly Highlights and Forecasts :Issued: 2001 Dec 26 2212 UT Highlights of Solar and Geomagnetic Activity 17 - 23 December 2001 Solar activity was at low to moderate levels during the period. Activity was low through 18 December with impulsive C-class subflares from a few moderately complex sunspots groups, which included Regions 9733, 9739, and 9742. Activity increased to moderate levels on 19 December due to an M1/Sf flare at 19/1706 UTC from Region 9739 (S13, L = 319, class/area Dko/440 on 17 December). This region rotated out of view on 20 December. Region 9733 (N14, L = 313, class/area Eki/560 on 12 December) produced isolated C-class subflares as it gradually decayed It also rotated out of view on 20 December. Activity returned to low levels during 20 – 22 December due to occasional C-class flares, mostly from Region 9742 (N10, L = 214, class/area Fkc/900 on 23 December). This region showed a steady increase in size and complexity during the period. Activity increased to moderate levels on 23 December by virtue of an M1/Sf flare at 23/2336 UTC from Region 9748 (S11, L = 191, class/area Dao/200 on 23 December). Region 9748 was in a gradual growth phase during this flare. Note: Region 9742 produced a major flare on 26 December. 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 high-speed stream associated with a coronal hole was observed during 17 – 18 December with velocities as high as 570 km/sec and elevated proton temperatures. These effects subsided late on 18 December. There was a period of increased velocities and temperatures during the latter half of 21 December. IMF Bz was southward most of 21 December, but was more strongly so during the latter half of the day with maximum deflections to minus 12 nT (GSM). There were no significant disturbances noted during the rest of the period. There were no proton events detected at geo-synchronous orbit. Note: greater than 100 MeV and greater than 10 MeV proton events began on 26 December following a major flare from Region 9742. Details will be provided in next week’s report. The greater than 2 MeV electron flux at geosynchronous orbit was at normal levels during most of the period. The geomagnetic field was at mostly quiet to unsettled levels through 20 December, although unsettled to minor storm conditions occurred at high latitudes during the latter half of 17 December. Activity increased to unsettled to active levels during the latter half of 21 December. Activity declined to quiet to unsettled levels during 22 – 23 December. Forecast of Solar and Geomagnetic Activity 26 December 2001 - 21 January 2002 Solar activity is expected to be at low to moderate levels during most of the period. Isolated, low-level M-class flares are expected. There will be a chance for isolated major flare activity as well. Region 9742 could produce a (another) major flare until it leaves the visible disk around 28 December. The greater than 100 MeV proton event that began on 26 December is expected to end late on 26 December or early on 27 December. The greater than 10 MeV proton event that began on 26 December is expected to continue for the next few days. There will be a chance for another proton event 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. Geomagnetic storm conditions may occur during 27 – 28 December due to a possible CME passage. Quiet to unsettled conditions are expected during most of the rest of the period. However, active conditions will be possible during 12 – 14 and 20 – 21 January due to coronal hole effects. .