Prepared jointly by the U.S. Dept. of Commerce, NOAA, Space Environment Center and the U.S. Air Force.

Updated 2004 Jul 25 2210 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity SDF Number 207 Issued at 2200Z on 25 Jul 2004

IA. Analysis of Solar Active Regions and Activity from 24/2100Z to 25/2100Z: Solar activity reached high levels today. Region 652 (N08W35) produced four M-class events, the largest - an M7/2B flare at 25/0551Z. This flare had associated moderate centimetric bursts, including an 819 sfu Tenflare. A Type IV radio sweep also accompanied this flare. No LASCO imagery was available, but it is likely that an Earth-directed CME was associated with this event. Lower, more impulsive M-class flares were observed at 25/0639Z and 25/1349Z. A long duration M1/1f flare erupted in Region 652 at 25/1514Z. Type II (898 km/s) and IV sweeps, and a greater than 10 MeV proton event accompanied this event. An 1818Z LASCO/C3 image exhibits a full halo CME associated with this long duration flare. Region 652 has shown some decay; however, it remains a large and complex beta-gamma-delta sunspot group with white light area coverage exceeding 1200 millionths. New Region 654 (N08E52) was numbered today.

IB. Solar Activity Forecast: Solar activity is expected to be moderate to high. Region 652 has decayed somewhat, but still maintains good potential for a major flare.

IIA. Geophysical Activity Summary 24/2100Z to 25/2100Z: The geomagnetic field was at active to severe storm levels. The shock observed at the ACE spacecraft on 24/0600Z was followed by a prolonged period of southward IMF Bz that lasted through midway on 25 July. Bz ranged from -10 to -20 nT for much of this period, while solar wind speed was elevated in the 550 to 700 km/s range. Consequently, severe geomagnetic storm levels were observed at all latitudes. It is likely that this activity was associated with the complex series of CMEs observed on 22 July. Late in this period, a discontinuity in the solar wind suggested that transient flow from the multiple CME activity on 23 July had arrived. A greater than 10 MeV proton event accompanied the long duration M1 flare and CME. The proton event began at 25/1855Z, and the peak so far was 41 pfu at 25/2100Z. The greater than 2 MeV electron flux at geosynchronous orbit was at high levels today.

IIB. Geophysical Activity Forecast: The geomagnetic field is expected to be at unsettled to severe storm levels. Minor to major storm periods are expected on day one as transient flow from the complex 23 July eruptions are expected to persist through much of 26 July. CMEs associated with today's M7 and long duration M1 flares will likely impact the geomagnetic field on 27 July and produce periods of major storming. Storm levels should subside by 28 July; a return to unsettled to active levels is expected by the end of the period. The greater than 10 MeV proton event in progress now, is expected to end on 26 July.

III. Event Probabilities 26 Jul-28 Jul

• Class M 70/65/60
• Class X 20/15/10
• Proton 90/25/10
• PCAF yellow

IV. Penticton 10.7 cm Flux

• Observed 25 Jul 145
• Predicted 26 Jul-28 Jul 140/140/135
• 90 Day Mean 25 Jul 105

V. Geomagnetic A Indices

• Observed Afr/Ap 24 Jul 029/027
• Estimated Afr/Ap 25 Jul 080/090
• Predicted Afr/Ap 26 Jul-28 Jul 050/075-060/055-030/030

VI. Geomagnetic Activity Probabilities 26 Jul-28 Jul

A. Middle Latitudes Ac

• tive 35/25/50
• Minor storm 40/45/25
• Major-severe storm 25/30/10

B. High Latitudes

• Active 20/25/55
• Minor storm 50/50/30
• Major-severe storm 30/25/15

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