Joint USAF/NOAA Report of Solar and Geophysical Activity 28 Jul 2004

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

Updated 2004 Jul 28 2210 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 210 Issued at 2200Z on 28 Jul 2004

IA. Analysis of Solar Active Regions and Activity from 27/2100Z
to 28/2100Z: Solar activity has declined to low levels. Region 652
(N08W76) continues to be quite active and produced several C-class
events this period. The most important was a very long duration C4
enhancement that began around 28/0200Z and lasted for 10 hours.
LASCO imagery showed a large CME off the west limb originating from
near Region 652. Though most of the ejecta was westward directed, a
glancing blow is possible from this CME. Region 652 continues to
slowly decay, but still maintains considerable size and magnetic
complexity. No other significant changes were noted.

IB. Solar Activity Forecast: Solar activity is expected to be very
low to moderate. Region 652 still has potential for an M-class flare
before it rotates around the west limb on 29 July. Expect levels to
decrease to very low to low by 30 July.

IIA. Geophysical Activity Summary 27/2100Z to 28/2100Z:
The geomagnetic field ranged from quiet to minor storm levels. The
period began with minor storm levels in the waning stages of
yesterday’s severe geomagnetic storm. By 28/0300Z, the IMF Bz was
near zero and the geomagnetic field responded with quiet to
unsettled conditions for the remainder of the period. Solar wind
speed was elevated near 900 km/s at the beginning of the period, but
gradually declined to 600 km/s. The greater than 10 MeV proton
event that began on 25/1855Z, ended on 28/0040Z. The greater than 2
MeV electron flux at geosynchronous orbit was at very high levels
today.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be quiet to unsettled on 29 July. Today’s CME off the
southwest limb is expected to produce unsettled to minor storm
periods late on 30 July. A gradual return to quiet to unsettled
conditions is expected on 31 July.

III. Event Probabilities 29 Jul-31 Jul

• Class M 40/20/05
• Class X 10/05/01
• Proton 15/05/05
• PCAF yellow

IV. Penticton 10.7 cm Flux

• Observed 28 Jul 101
• Predicted 29 Jul-31 Jul 090/080/080
• 90 Day Mean 28 Jul 106

V. Geomagnetic A Indices

• Observed Afr/Ap 27 Jul 119/162
• Estimated Afr/Ap 28 Jul 012/015
• Predicted Afr/Ap 29 Jul-31 Jul 012/015-020/030-015/020

VI. Geomagnetic Activity Probabilities 29 Jul-31 Jul

A. Middle Latitudes

• Active 25/35/25
• Minor storm 10/15/10
• Major-severe storm 01/05/05

B. High Latitudes

• Active 30/45/35
• Minor storm 15/20/15
• Major-severe storm 05/10/05