Joint USAF/NOAA Report of Solar and Geophysical Activity 17 Sep 2004

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

Updated 2004 Sep 17 2210 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 261 Issued at 2200Z on 17 Sep 2004

IA. Analysis of Solar Active Regions and Activity from 16/2100Z
to 17/2100Z: Solar activity has been very low. X-ray flux has
remained at background levels. Surging was observed from Region 673
(S13E51), and the region grew slightly over the period to 320
millionths in white light. No new regions were numbered today.

IB. Solar Activity Forecast: Solar activity is expected to be very
low to low. Regions 672 (N05W29) and 673 are capable of C-class
flares.

IIA. Geophysical Activity Summary 16/2100Z to 17/2100Z:
The geomagnetic field was at quiet to minor storm levels, most likely
caused by the increased solar wind from a geoeffective coronal hole.
Solar wind speed at ACE began to diminsh around 0900 UTC and was at
approximately 450 km/s at the end of the period. The greater than 2
MeV electron flux at geosynchronous orbit reached high levels today.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be quiet to unsettled.

III. Event Probabilities 18 Sep-20 Sep

• Class M 20/20/20
• Class X 01/01/01
• Proton 01/01/01
• PCAF green

IV. Penticton 10.7 cm Flux

• Observed 17 Sep 105
• Predicted 18 Sep-20 Sep 105/105/100
• 90 Day Mean 17 Sep 111

V. Geomagnetic A Indices

• Observed Afr/Ap 16 Sep 014/017
• Estimated Afr/Ap 17 Sep 015/020
• Predicted Afr/Ap 18 Sep-20 Sep 010/015-010/012-008/012

VI. Geomagnetic Activity Probabilities 18 Sep-20 Sep

A. Middle Latitudes

• Active 30/30/30
• Minor storm 05/05/05
• Major-severe storm 01/01/01

B. High Latitudes

• Active 40/35/30
• Minor storm 25/25/20
• Major-severe storm 15/10/10