Joint USAF/NOAA Report of Solar and Geophysical Activity 25 Apr 2003

SDF Number 115 Issued at 2200Z on 25 Apr 2003

IA. Analysis of Solar Active Regions and Activity from 24/2100Z
to 25/2100Z: Solar activity remained at moderate levels today. The
largest flare of the period was an M1/Sf which occurred at 25/0540Z
from Region 346 (N16E61) and had an associated Type II radio sweep
with an estimated shock velocity of 814 km/s. There seems to be
little magnetic complexity to this region based on a single Hsx spot
seen in white-light. Region 337 (S14W13) appears to have changed
little since yesterday and remains a beta-gamma magnetic complex.
Region 338 (N18W58) produced the majority of the flare activity
throughout the interval which was limited to C-class events.
Magnetically, this region appears to be in a decay phase as a
single delta complex remains apparent verses the several complexes
analyzed earlier in the period. No new regions were numbered today.

IB. Solar Activity Forecast: Solar activity is expected to be at
low to moderate levels. Region 338 remains capable of producing
M-class events.

IIA. Geophysical Activity Summary 24/2100Z to 25/2100Z:
The geomagnetic field was at predominantly active to minor storm
levels. High speed solar wind speeds along with embedded transient
activity are believed to be responsible for the elevated conditions.
The greater than 2 MeV electron fluxes at geosynchronous orbit
reached high levels again today.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be at active to minor storm levels with isolated major
storm conditions possible throughout the period. High speed coronal
hole flow may continue to be enhanced by transient activity for the
entire interval. A weak CME impact from the M5 flare on April 23 is
possible on day one. Further CME effects are possible on day two
resulting from the M3 flare that occurred on 24 April. The M1 that
occurred today may have a very weak impact late on day two into day
three.

III. Event Probabilities 26 Apr-28 Apr

• Class M 50/50/50
• Class X 05/05/05
• Proton 05/05/05
• PCAF green

IV. Penticton 10.7 cm Flux

• Observed 25 Apr 144
• Predicted 26 Apr-28 Apr 145/150/145
• 90 Day Mean 25 Apr 126

V. Geomagnetic A Indices

• Observed Afr/Ap 24 Apr 024/024
• Estimated Afr/Ap 25 Apr 020/025
• Predicted Afr/Ap 26 Apr-28 Apr 020/025-020/025-015/020

VI. Geomagnetic Activity Probabilities 26 Apr-28 Apr

A. Middle Latitudes

• Active 45/45/30
• Minor storm 25/25/20
• Major-severe storm 15/15/10

B. High Latitudes

• Active 40/40/45
• Minor storm 30/30/25
• Major-severe storm 20/20/15