:Product: Weekly Highlights and Forecasts :Issued: 2003 Apr 29 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 21 - 27 April 2003 Solar activity ranged from low to high levels. The period was marked by significant activity form Region 338 (N18, L=285, class/area Eac/250 on 26 April), which produced nine M-class flares and numerous C-class flares. The largest event during the period was an M7 flare on 26 April as described below. Region 339 (N18, L=338, class/area Cso/60 on 23 April) was also very active, producing twelve C-class flares as it transited the west limb on 23 – 24 April. Region 346 (N16, L=165, class/area Cso/60 on 26 April) rotated onto the visible disk on 24 April as a small magnetically simple spot group, but produced an M-class flare on the 25th. Region 349 (S14, L= 154, class/area Dao/150 on 27 April) appeared on the visible disk late in the period and was in a significant growth phase through the end of the period. The period began on 21 April, with moderate level activity due to an M2/1n flare from Region 338. This M2 flare was associated with a Type II (1200 km/s) and Type IV radio sweep, 300 sfu Ten-flare radio burst, and a partial halo CME. This region exhibited steady growth throughout much of the period and developed a beta-gamma-delta magnetic configuration on 25 April. Activity decreased to low levels on 22 April due to four C-class flares from Region 338. A Type II (960 km/s) radio sweep was reported on 22 April at 0716 UTC and analysis of NOAA/SXI imagery indicates the source as a CME on the east limb. On 23 April, activity reached high levels with an M5/1n flare from Region 338. The M5 was associated with a Type II (513 km/s) and Type IV radio sweep, 380 sfu Ten-flare radio burst, and a partial halo CME. On 24 - 25 April, activity returned to moderate levels due to an M3/1n flare from Region 338 on the 24th and an M1/Sf flare from Region 346 on the 25th. The M3 flare was associated with a Type II (830 km/s) and Type IV radio sweep as well as a partial halo CME. The M1 flare on the 25th was associated with a Type II (814 km/s) radio sweep and a CME off the east limb. Region 338 also produced seven C-class flares on the 25th. High level activity was observed on 26 April with Region 338 producing four M-class flares and over 8 C-class flares, the largest of which was an impulsive M7. The period ended on 27 April with moderate activity due to a single M1/Sf flare from Region 338. Region 338 also produced numerous C-class flares on the 27th as it approached the west limb. For flare times and magnitudes please refer the Energetic Event and Flare lists. Solar wind data were available from the NASA Advanced Composition Explorer (ACE) spacecraft for most of the summary period. Solar wind speed increased on 21 – 22 April to near 600 km/s. On 23 - 24 April, solar wind speed was in gradual decline but still elevated. By midday on 24 April, solar wind began to rise again and peaked near 600 km/s on 25 April due to a combination of high speed flow and transient flow. Solar wind speed declined on 26 April to 425 km/s but gradually, increased on 27 April to end the period near 550 km/s due to a high speed coronal hole stream. There were no greater than 10 MeV proton events at geo-synchronous orbit during the summary period. The greater than 2 MeV electron flux at geo-synchronous orbit reached high levels everyday of the period, 21 – 27 April. The geomagnetic field ranged from quiet to minor storm levels. The period began on 21 – 23 April with a coronal hole high speed flow resulting in unsettled to active conditions with isolated minor storm levels on the 21st and the 23rd. A transient flow was observed on 24 – 25 April and resulted in unsettled to minor storm levels. The period ended on 26 – 27 April with gradually increasing solar wind speed, which produced unsettled to active levels. Forecast of Solar and Geomagnetic Activity 30 April - 26 May 2003 Solar activity is expected to be at low to moderate levels. Region 349 is expected to have M-class potential early in the period as it continues to grow and develop in magnetic complexity. Activity is expected to decrease to low levels after 06 May when Region 349 rotates beyond the west limb. Region 338 is due to return to the visible disk on 11 May and represents M-class potential for the remainder of the period. No greater than 10 MeV proton events are expected during the forecast period. The greater than 2 MeV electron flux may reach high levels on 01 – 10 May, and again on 16 – 23 May due to returning coronal holes. The geomagnetic field is expected to range from quiet to isolated major storm levels. Unsettled to major storm levels are possible early in the period, 29 April – 02 May, due to a coronal hole high speed flow. Multiple returning coronal holes are expected to rotate into geo-effective positions during the latter half of the period, and are expected to produce unsettled to minor storm conditions. On 13 – 14 May, isolated major storm levels are possible with the return of a large coronal hole high speed flow.