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

SDF Number 138 Issued at 2200Z on 18 May 2003

IA. Analysis of Solar Active Regions and Activity from 17/2100Z
to 18/2100Z: Solar activity was low. Region 357 (S16W20) produced
the only C-class flare of the period – a C1 flare at 18/1057Z. This
region has shown little change over the past 24 hours, maintaining a
simple beta configuration. Region 362 (S11E37) appeared to develop
some complexity early in the period, but has since stabilized. New
Region 363 (S08W04) was numbered today.

IB. Solar Activity Forecast: Solar activity is expected to continue
at low levels. Regions 357 and 362 have potential for low C-class
activity. Activity is expected to increase later in the week with
the return of a zone of active longitudes that contained old Regions
345 (S17, L=167), 348 (S35, L=149), and 349 (S14, L=153).

IIA. Geophysical Activity Summary 17/2100Z to 18/2100Z:
The geomagnetic field was quiet to unsettled. Slightly enhanced solar
wind conditions occurred late in the period and produced the
unsettled conditions. The greater than 2 MeV electrons at
geosynchronous orbit reached very high levels today.

IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to range from quiet to active. Increased solar wind speed,
associated with a favorably positioned coronal hole will cause
occasional disturbed periods through day two.

III. Event Probabilities 19 May-21 May

• Class M 10/10/10
• Class X 01/01/01
• Proton 01/01/01
• PCAF green

IV. Penticton 10.7 cm Flux

• Observed 18 May 109
• Predicted 19 May-21 May 115/120/130
• 90 Day Mean 18 May 124

V. Geomagnetic A Indices

• Observed Afr/Ap 17 May 006/009
• Estimated Afr/Ap 18 May 007/009
• Predicted Afr/Ap 19 May-21 May 015/015-012/012-010/010

VI. Geomagnetic Activity Probabilities 19 May-21 May

A. Middle Latitudes

• Active 30/25/20
• Minor storm 10/10/05
• Major-severe storm 05/05/05

B. High Latitudes

• Active 40/35/30
• Minor storm 20/15/15
• Major-severe storm 10/05/05