:Product: Weekly Highlights and Forecasts :Issued: 2004 Dec 29 1432 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 20 - 26 December 2004 Solar activity was very low to low this period. The period began with very low conditions on 20 and 21 December. Region 713 (S09, L=124, class/area, Eai/210, on 20 December) developed a beta gamma magnetic classification early in the period and produced several C-class events on 22 and 23 December. The largest of these flares was a C5 at 23/1008Z. On 24 December, a C1 long duration flare occurred from a spotless area in the southeast quadrant at 0356Z. A CME on LASCO imagery was likely associated with this flare but was not earth directed. On 25 and 26 December, very low levels were experienced again as Region 713 showed signs of decay in both sunspot number and area. Solar wind data were available from the NASA Advanced Composition Explorer (ACE) spacecraft during most of the summary period. The period began with solar wind speed near 400 km/s. Solar wind speed was in a decline phase following a geoeffective coronal hole high speed stream (HSS). On 21 December, ACE data indicated the presence of a co-rotating interaction region (CIR) with the IMF Bz fluctuating between +10 and -14 nT. This CIR was followed on 22 December by a high speed stream from a geoeffective coronal hole. Wind speed reached approximately 550 km/s on 22 December and declined to 400 km/s by the end of the UTC day on 23 December. ACE data indicated the onset of another weak CIR and coronal hole HSS on 25 December. Solar wind speed climbed to approximately 500 km/s and remained above 500 km/s through the end of the reporting period. No greater than 10 MeV proton events were observed this period. The greater than 2 MeV electron flux at geosynchronous orbit increased to high levels on 20 December. The geomagnetic field ranged from quiet to minor storm levels with isolated major storm periods at high latitudes. The period began with quiet levels. On 21 and 22 December, mostly quiet to unsettled with isolated periods of minor storming, and major storm periods at high latitudes, were observed due to a high speed stream. Quiet conditions prevailed on 23 and 24 December. On 25 December, quiet to active conditions were observed due to the influence of another high speed stream. This stream continued to influence the geomagnetic field on 26 December, however only quiet to unsettled conditions were experienced. Forecast of Solar and Geomagnetic Activity 29 December 2004 - 24 January 2005 Solar activity is expected to be very low to low with a chance of M-class activity from Region 713 and 715 (N04, L=339, class/area, Dao/80, on 28 December). Region 713 will be departing the visible disk on 30 December and Region 715 will be departing on 10 January. Expect very low to low conditions after 10 January. Solar activity is expected to be very low to low with a chance of M-class activity from Region 713 and 715 (N04, L=339, class/area, Dao/80, on 28 December). Region 713 will be departing the visible disk on 30 December and Region 715 will be departing on 10 January. Expect very low to low conditions after 10 January. A greater than 10 MeV proton event is not expected. The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at high levels on 03-04, 14-15, 18-19, and 22-23 January. The geomagnetic field is expected to range from mostly quiet to active levels with isolated minor storm periods. High speed coronal hole streams are expected to produce occasional storm periods on 02–03, 13-14, 17-18, and 21-22 January. Otherwise, expect quiet to unsettled conditions.