:Product: Weekly Highlights and Forecasts :Issued: 2002 Apr 23 2212 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 15 - 21 April 2002 Solar activity ranged from low to high levels. Activity was moderate during 15 – 17 April due to lesser M-class flares from adjacent Regions 9893 (N19, L = 215, class/area Eai/490 on 09 April) and 9901 (N20, L = 204, class/area Dai/250 on 13 April), and Region 9906 (S16, L = 151, class/area Eki/640 on 14 April). The 9893/9901 region complex rotated out of view on 16 April. Region 9906 produced two long-duration lesser M-class flares on 15 and 17 April, each associated with an Earth-directed halo CME (for flare times and magnitudes, please refer to the Energetic Events or Optical Flares listings). One of these, an M2/2n at 17/0824 UTC, was associated with Types II and IV radio sweeps, a 3000 sfu Tenflare and a solar proton event (see the discussion below). Activity dropped to low levels during 18 – 20 April due to C-class subflares, most of which were produced by Region 9906. Activity increased to high levels on 21 April as Region 9906 produced a long-duration X1/1f flare at 21/0151 UTC while crossing the west limb. This spectacular flare was associated with a 1900 sfu Tenflare, Types II and IV radio sweeps, multiple eruptive prominences, a solar proton event, and a partial-halo CME. Region 9906 began to gradually decay on 18 April, but remained large and complex until it crossed the west limb on 21 April. Solar wind data were available from NASA Advanced Composition Explorer (ACE) spacecraft for most of the summary period. Coronal mass ejections encountered Earth on 17 and 19 April following flare activity from Region 9906. The 17 April passage began at approximately 17/1022 UTC and was associated with high solar wind speeds (peaks to 620 km/sec) as well as a period of sustained southward IMF Bz (approximately17/1400 – 2000 UTC) with maximum southerly deflections to minus 28 nT (GSM). The 19 April passage began at approximately 19/0804 UTC and was associated with velocities as high as 700 km/sec and prolonged periods of southward IMF Bz on 19 and 20 April with peak southerly deflections to minus 17 nT (GSM). A greater than 10 MeV proton event began at geo-synchronous orbit at 17/1530 UTC, reached a peak of 24 pfu at 17/1540 UTC, then ended at 18/0035 UTC. Greater than 100 MeV and greater than 10 MeV proton events followed the X1 flare of 21 April. The greater than 100 Mev event began at 21/0155 UTC, reached a peak of 22.9 pfu at 21/1025 UTC, and was in progress as the period ended. The greater than 10 MeV event began at 21/0225 UTC, reached a peak of 2520 pfu at 21/2320 UTC, and was also in progress as the period ended. Greater than 2 MeV electron fluxes at geo-synchronous orbit were at normal to moderate levels during most of the period. Geomagnetic field activity was at quiet to unsettled levels during 15 – 16 April. Activity increased to active to major storm levels on 17 April following a sudden storm commencement (SSC) at 17/1109 UTC (57 nT, Boulder USGS magnetometer). The storm continued into 18 April with active to severe storm levels during the first half of the day and mostly active levels thereafter. Another SSC occurred at 19/0836 UTC (36 nT, Boulder USGS magnetometer) followed by active to severe storm levels that continued into 20 April. The disturbance subsided late on 20 April. Quiet to unsettled levels occurred during the remainder of the period. Forecast of Solar and Geomagnetic Activity 24 April - 20 May 2002 Solar activity is expected to be at low to moderate levels during the period. Isolated low-level M-class flares are likely, particularly during the latter half of the outlook period. There will be a chance for isolated major flare activity during the latter half of the period as well. The greater than 10 MeV proton event that began on 21 April is expected to end on 25 April (the greater than 100 MeV event ended at 23/2335 UTC). Chances for a proton flare may increase during 10 – 17 May. Greater than 2 MeV fluxes may reach high levels around 30 April – 02 May. Normal to moderate flux levels are expected during the rest of the period. Geomagnetic field activity is expected to be at quiet to unsettled levels during most of the period. However, active conditions will be possible on 24 April and during 27 – 30 April. .