Space Weather Highlights SWO PRF 1508 
19 – 25 July 2004 27 Jul 2004 
Solar activity levels ranged from low to high. The summary period began with activity at low levels as 
numerous C-class flares were observed from Region 649 (S10, L=044, class/area, Eac/370 on 19 July) and 
Region 652 (N08, L=345, class/area, Fkc/2010 on 21 July). By 20 July, activity levels rose to high as Region 
652 produced an M8/3b flare at 1232 UTC. Associated with this flare was a 3000 sfu Tenflare, a Type II 
radio sweep with an estimated shock velocity of 485 km/s, and a Type IV sweep. In conjunction with this 
event, a C6/Sf flare occurred at 20/1126 UTC and had an associated full-halo CME on LASCO imagery. By 
21 July, activity levels decayed to low, but by early on 22 July, levels rose to high. At 22/0032 UTC, Region 
652 produced an M9 flare as well as several C-class flares during the period from 0633 to 0808 UTC. Two 
CMEs occurred simultaneously which formed a faint full halo CME signature on LASCO imagery. Moderate 
levels returned on the 23rd with three M-class flares observed from Region 652, the largest event was an 
M2/Sf at 23/1728 UTC. A CME with a plane-of-sky speed of 700 km/s was observed with this flare. Earlier 
in the day, at 23/1609 UTC, Region 652 produced a C1 flare with an associated Type II (710 km/s) radio 
sweep. LASCO imagery observed another full-halo CME from this flare. Moderate levels remained on 24 
July with three M-class flares observed from Region 652. Three CMEs were observed on LASCO imagery, 
although none were Earth directed. Solar activity levels reached high on 25 July as four M-class flares were 
observed from Region 652, the largest was an M7/2b that occurred at 25/0551 UTC. Associated with this 
flare were moderate centimetric bursts including an 819 sfu Tenflare, and a Type IV radio sweep. A weak, 
non-Earth directed CME accompanied this event. At 25/1514 UTC, a long duration M1/1f flare erupted in 
Region 652 with Type II (898 km/s) and Type IV radio sweeps. LASCO imagery indicated that an Earth 
directed, full-halo CME accompanied this event. By the end of the summary period, Region 652 had shown 
some decay; however, it remained a large and complex beta-gamma-delta sunspot group. 
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 but by early on 20 July, 
velocity increased to near 600 km/s. Wind speed fluctuated between 500 and 600 km/s throughout the 20th, 
but had decayed to 425 km/s by the end of the 21st. Through midday on 22 July, the IMF Bz fluctuated 
between +5 to -5 nT. At 22/1028 UTC, a geomagnetic sudden impulse was observed, followed by a steady 
increase in solar wind speed to near 700 km/s and a southward turning of the Bz to -19 nT. This transient was 
believed to have been the result of CME activity seen on 20 July. Speed decreased to near 500 km/s by 
midday on 23 July and remained so until a weak sudden impulse was observed at ACE on 24/0600 UTC. 
Wind speed increased to 600 km/s and remained so throughout the 24th. The IMF Bz responded with a 
southward turning to –20 nT during this period. This transient was likely associated with the complex series 
of CMEs observed on 22 July. Late in the summary period, a discontinuity in the solar wind suggested that 
transient flow from CME activity on 23 July arrived. Wind speed responded with an increase in velocity to 
near 700 km/s while the IMF Bz ranged from +5 to –12nT. 



As the period ended, a greater than 10 MeV proton event was in progress associated with the long duration 
M1 flare on 25 July. The event began at 25/1855 UTC and reached a peak of 55 pfu at 25/2305 UTC. The 
proton event was still in progress at this writing. 
The greater than 2 MeV electron flux at geosynchronous orbit was at high levels on 23 – 25 July. 
The geomagnetic field ranged from quiet to severe storm levels. The first three days of the summary period 
were dominated by quiet to unsettled geomagnetic conditions. Late on 22 July, minor to major storm 
conditions were observed and persisted throughout most of 23 July. This activity was most likely the result of 
CME activity from 20 July. By the end of 23 July, activity levels had decreased to mostly quiet to unsettled. 
Early on 24 July, activity levels increased to active to minor storming and by 25 July, activity levels further 
increased to major to severe storming as transient effects from the series of CMEs from 22 and 23 July made 
their presence felt.