:Product: Weekly Highlights and Forecasts :Issued: 2005 Sep 20 2154 UTC # Prepared by the US Dept. of Commerce, NOAA, Space Environment Center # Product description and SEC contact on the Web # http://www.sec.noaa.gov/weekly.html # # Weekly Highlights and Forecasts # Highlights of Solar and Geomagnetic Activity 12 - 18 September 2005 Solar activity ranged from low to high levels. The most active region on the disk remained Region 808 (S09, L=232, class/area, Fkc/1430 on 09 September) which produced several major flares this period. During the summary period, the region produced 28 C-class, 8 M-class, and 3 X-class flares. Late on 13 September, Region 808 produced a pair of X-class events responsible for a strong, complex, frontsided, asymmetric full halo CME. The first event was a double peak, X1.5/2b long duration event at 13/1927 UTC with an associated 6000 sfu 10cm radio burst, while the second event was an X1.7/1b at 12/2322 UTC with an associated 180 sfu 10cm radio burst. Since 14 September, the region has shown signs of significant decay in white light. Region 808 has produced 13 major flares greater than or equal to M5, to include ten X-class and three M5 or higher M-class flares. Based on this criteria (greater than or equal to M5 flares) alone, Region 808 produced more major flares than any other region in Solar Cycle 23. Solar wind data were available from the NASA Advanced Composition Explorer (ACE) spacecraft during most of the summary period. Solar wind speed at ACE was elevated at the beginning of the summary period at near 800 km/s due to CME effects from the X6 flare of 09 September. At about 12/0600 UTC, another shock was observed at ACE, as solar wind speed measurements increased to about 1000 km/s, and the IMF Bz fluctuated between +/- 10 nT for about six hours. This shock was assumed to be associated with the long duration X2 flare and CME on 10 September. By midday on 12 September, solar wind velocity began to decrease, and by early on 15 September, had decayed to near 600 km/s. During this same period, the Bz component of the IMF did not vary much beyond +/- 5 nT. At 15/0907 UTC, a 29 nT sudden impulse was observed at the Boulder magnetometer as a shock from the CME activity associated with the double X-class flare on 13 September arrived at Earth. Solar wind speed rose from about 600 km/s to near 900 km/s, while the IMF had periods of southward Bz to -15 nT for a six hour period. The summary period ended with the solar wind speed at near 550 km/s and a weak IMF Bz not varying much beyond +/- 5 nT. A greater than 10 MeV proton event that began early on 08 September as a result of the X17 flare on the 7th, finally ended early on 16 September. The event began at 08/0215 UTC, reached an initial peak of 1880 pfu on 11/0425 UTC, and fell below event threshold late on 12 September. A second infusion of greater than 10 MeV energetic protons from the CME and X-class activity late on the 13th saw a second, weaker max of 235 pfu at 15/0905 UTC. The event finally ended at 16/0025 UTC. A greater than 100 MeV proton event began at 08/0405 UTC, maxed at 8 pfu on 09/1920 UTC, and ended at 11/0545 UTC. The greater than 2 MeV electron flux at geosynchronous orbit was at high levels 11 - 16 September and very high levels on 17 and 18 September. The geomagnetic field ranged from quiet to severe storm levels. Predominantly active to minor storm levels at middle latitudes, and major to severe storm levels at high latitudes persisted through midday on 13 September, as CME effects from the X6 flare of 09 September persisted. Conditions relaxed to mostly quiet to unsettled through early on 14 September. By 14/0900 UTC, geomagnetic activity increased to unsettled to active levels at middle latitudes, and major to severe storm levels at high latitudes, as transient effects from CME activity continued. By midday on 15 September, minor storm levels were present at middle latitudes. By late on the 15th, conditions at all latitudes relaxed to mostly unsettled to active. However, by 16/0900 UTC, activity levels increased once again as CME effects from the double X-class flare and CME of 13 September became geoeffective. Activity levels remained mostly unsettled to active at middle latitudes, but at high latitudes, activity increased to major to severe storm levels for about six hours, and subsequently relaxed to minor to major storm levels through midday on the 18th. Thereafter, and for the remainder of the summary period, the field was quiet at all latitudes. Forecast of Solar and Geomagnetic Activity 21 September - 17 October 2005 Solar activity is expected to be at mostly very low to low levels. Region 808 has shown significant decay in white light; therefore, the potential for major flare activity from this region has been significantly reduced. No greater than 10 MeV proton events are expected. The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at high levels on 21 – 24 September and high again on 29 September – 17 October. The geomagnetic field is expected to range from quiet to minor storm levels. Active to minor storm conditions are possible on 28 – 29 September, while unsettled to active conditions are possible on 12 - 13 October, both due to recurrent coronal hole high speed wind streams.