Joint USAF/NOAA Report of Solar and Geophysical Activity 12 Apr 2004

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

Updated 2004 Apr 12 2210 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity

SDF Number 103 Issued at 2200Z on 12 Apr 2004

IA. Analysis of Solar Active Regions and Activity from 11/2100Z
to 12/2100Z: Solar activity was at low levels. Region 588 (S15W68)
produced multiple C-class flares today. The largest was a C2/Sf
event that occurred at 12/0225Z. This region remains a reverse
polarity beta magnetic configuration. Updated LASCO imagery
indicates two separate occurrences of CME activity yesterday. A
partial halo CME was observed in response to the C9/Sf event
(erupted at 11/0419Z) that indicates potential for a glancing blow
from the likeliness of a resulting shock passage. The second, a
full halo CME first seen in C2 at 11/1154Z, was determined to be
backsided. New Region 591 (S15E01) was numbered today.

IB. Solar Activity Forecast: Solar activity is expected to be at
very low to low levels.

IIA. Geophysical Activity Summary 11/2100Z to 12/2100Z:
The geomagnetic field was at quiet to active levels. A shock passage
was observed at the ACE spacecraft at approximately 12/1730Z and it
is believed to be in response to the partial halo CME that was
associated with the C2 flare that occurred on 09/2040Z. Once again,
the IMF Bz remained predominantly northward and the geomagnetic
response was weak. Solar wind speeds peaked at near 540 km/s
shortly after the shock passage and has decreased to approximately
440 km/s at the time of this writing. The greater than 10 MeV
proton event that began at 11/1135Z, peaked at 35 pfu at 11/1845Z,
and ended at 12/0405Z. The greater than 2 MeV electron flux at
geosynchronous orbit reached high levels today.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to range from quiet to active levels. Minor storm
conditions may occur on 13 April in response to a shock passage from
yesterdays C9 flare and the associated partial halo CME. 14 and 15
April should see a return to predominantly unsettled levels with the
potential for active conditions, mostly in high latitude nighttime
sectors.

III. Event Probabilities 13 Apr-15 Apr

• Class M 15/15/10
• Class X 01/01/01
• Proton 10/05/01
• PCAF green

IV. Penticton 10.7 cm Flux

• Observed 12 Apr 091
• Predicted 13 Apr-15 Apr 095/100/105
• 90 Day Mean 12 Apr 109

V. Geomagnetic A Indices

• Observed Afr/Ap 11 Apr 006/008
• Estimated Afr/Ap 12 Apr 012/012
• Predicted Afr/Ap 13 Apr-15 Apr 015/020-012/015-010/012

VI. Geomagnetic Activity Probabilities 13 Apr-15 Apr

A. Middle Latitudes

• Active 30/25/20
• Minor storm 15/10/10
• Major-severe storm 10/05/05

B. High Latitudes

• Active 40/30/20
• Minor storm 20/15/10
• Major-severe storm 10/10/05