Joint USAF/NOAA Report of Solar and Geophysical Activity 21 Sep 2004

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

Updated 2004 Sep 21 2200 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 265 Issued at 2200Z on 21 Sep 2004

IA. Analysis of Solar Active Regions and Activity from 20/2100Z
to 21/2100Z: Solar activity was low. Region 672 (N04W86) produced a
C7.5 flare at 0836Z. Region 672 will rotate around the west limb on
22 September. Region 673 (S13W04), the only other sunspot group on
the visible disk, is in a slow decay phase. No new regions were
numbered.

IB. Solar Activity Forecast: Solar activity is expected to be very
low with a slight chance for C-class flares from Region 673 and 672
as it rotates around the west limb.

IIA. Geophysical Activity Summary 20/2100Z to 21/2100Z:
The geomagnetic field was quiet to unsettled with an isolated active
period between 0300Z to 0600Z. The active conditions followed a
period of southward IMF Bz. Solar wind plasma and magnetic field
measurements indicate the presence of a weak coronal hole stream.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be quiet to active with a possibility of reaching minor
storm levels on 22 September. Active to minor storm periods are
possible on the 22nd due to a weak high speed solar wind stream and
the expected impact of a CME that occurred late on 19 September.
Levels are expected to return to quiet to unsettled with isolated
active periods on 23-24 September.

III. Event Probabilities 22 Sep-24 Sep
Class M 05/05/05
Class X 01/01/01
Proton 05/05/01
PCAF green

IV. Penticton 10.7 cm Flux
Observed 21 Sep 095
Predicted 22 Sep-24 Sep 090/090/090
90 Day Mean 21 Sep 112

V. Geomagnetic A Indices
Observed Afr/Ap 20 Sep 008/013
Estimated Afr/Ap 21 Sep 008/010
Predicted Afr/Ap 22 Sep-24 Sep 020/025-010/015-008/010

VI. Geomagnetic Activity Probabilities 22 Sep-24 Sep
A. Middle Latitudes
Active 35/30/20
Minor storm 15/10/05
Major-severe storm 05/05/01
B. High Latitudes
Active 45/35/30
Minor storm 25/20/10
Major-severe storm 10/10/01