Joint USAF/NOAA Report of Solar and Geophysical Activity 18 Aug 2003

SDF Number 230 Issued at 2200Z on 18 Aug 2003

IA. Analysis of Solar Active Regions and Activity from 17/2100Z
to 18/2100Z: Activity was at low levels. Region 431 (S10W52)
produced a C2/Sf flare at 18/0906Z as it continues to decay. Region
436 (N08E57) rotated further onto the visible disk revealing 160
millionths in area coverage and a beta magnetic configuration.

IB. Solar Activity Forecast: Activity is expected to be a low
levels. There is a slight chance of an isolated M-class event from
Region 431 or Region 436.

IIA. Geophysical Activity Summary 17/2100Z to 18/2100Z:
The geomagnetic field was at active to severe storm levels. Around
18/0100Z the Bz component of the interplanetary magnetic field
turned southward to -15 nT with a peak near -25 nT. This shift in
Bz resulted in sustained minor to severe storm levels until
18/1500Z. Solar wind data are consistent with an interplanetary
transient. Re-analysis of solar data for the past few days indicate
activity in Region 431 (near center disk) late on 14 August as a
possible source of this storm.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to range from quiet to minor storm levels. Geomagnetic
storming is expected diminish on day one with isolated minor storm
levels possible. Quiet to unsettled conditions are expected on day
two and day three of the period.

III. Event Probabilities 19 Aug-21 Aug

• Class M 30/25/25
• Class X 05/05/05
• Proton 01/01/01
• PCAF green

IV. Penticton 10.7 cm Flux

• Observed 18 Aug 116
• Predicted 19 Aug-21 Aug 115/115/110
• 90 Day Mean 18 Aug 127

V. Geomagnetic A Indices

• Observed Afr/Ap 17 Aug 010/015
• Estimated Afr/Ap 18 Aug 062/082
• Predicted Afr/Ap 19 Aug-21 Aug 020/025-015/015-015/015

VI. Geomagnetic Activity Probabilities 19 Aug-21 Aug

A. Middle Latitudes

• Active 40/20/20
• Minor storm 25/05/05
• Major-severe storm 10/01/01

B. High Latitudes

• Active 50/25/25
• Minor storm 30/10/10
• Major-severe storm 15/01/01