Joint USAF/NOAA Report of Solar and Geophysical Activity 26 Jul 2004

Prepared jointly by the U.S. Dept. of Commerce, NOAA,
Space Environment Center and the U.S. Air Force.
Updated 2004 Jul 26 2210 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 208 Issued at 2200Z on 26 Jul 2004

IA. Analysis of Solar Active Regions and Activity from 25/2100Z
to 26/2100Z: Solar activity was moderate. Region 652 (N08W47)
produced two M-class flares – an M1/Sf at 26/0552Z, and an M1/2n at
26/1730Z. This region continues in a slow decay phase, but still
exceeds 1000 millionths of white light area coverage in a moderately
complex beta-gamma-delta configuration. Growth was observed in
newly numbered Region 654 (N07E38), but no activity of note has
occurred. The remainder of the disk and limb was quiet.

IB. Solar Activity Forecast: Solar activity is expected to be
moderate. Region 652 will likely produce further M-class activity
and still maintains potential for a major flare.

IIA. Geophysical Activity Summary 25/2100Z to 26/2100Z:
The geomagnetic field ranged from quiet to severe storm levels. The
severe geomagnetic storm that occurred yesterday, continued into the
early hours of this period. Major to severe geomagnetic storm
periods were observed through 26/0300Z. Solar wind speed remained
elevated from 500 to over 700 km/s, but IMF Bz was generally around
zero from 0300Z through the end of the period. Consequently, the
geomagnetic field was mostly quiet to unsettled. The greater than 10
MeV proton event that began yesterday at 25/1855Z, is still in
progress. The peak so far was 271 pfu at 26/1905Z. The greater than
2 MeV electrons at geosynchronous orbit reached high levels today.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to range from quiet to major storm levels. A full halo CME
was observed on LASCO imagery following yesterday’s long duration M1
flare at 25/1514Z. This CME will likely impact the geomagnetic field
early on 27 July. Expect minor to major storm periods at all
latitudes and severe storm levels at high latitudes. The storm is
expected to end by 28 July. Mostly unsettled to active conditions
are expected on 28 July. A return to quiet to unsettled levels is
expected on 29 July with isolated high latitude active period
possible. The greater than 10 MeV proton event in progress now will
likely end on 28 July.

III. Event Probabilities 27 Jul-29 Jul

• Class M 65/65/50
• Class X 15/10/10
• Proton 90/25/10
• PCAF red

IV. Penticton 10.7 cm Flux

• Observed 26 Jul 128
• Predicted 27 Jul-29 Jul 125/120/115
• 90 Day Mean 26 Jul 105

V. Geomagnetic A Indices

• Observed Afr/Ap 25 Jul 064/122
• Estimated Afr/Ap 26 Jul 020/040
• Predicted Afr/Ap 27 Jul-29 Jul 060/055-025/030-015/020

VI. Geomagnetic Activity Probabilities 27 Jul-29 Jul

A. Middle Latitudes

• Active 20/40/20
• Minor storm 40/20/10
• Major-severe storm 40/10/05

B. High Latitudes

• Active 20/50/30
• Minor storm 30/25/15
• Major-severe storm 50/15/05