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
