:Product: 20010410RSGA.txt :Issued: 2001 Apr 10 2200 UTC # Prepared jointly by the U.S. Dept. of Commerce, NOAA, # Space Environment Center and the U.S. Air Force. # Joint USAF/NOAA Report of Solar and Geophysical Activity SDF Number 100 Issued at 2200Z on 10 Apr 2001 IA. Analysis of Solar Active Regions and Activity from 09/2100Z to 10/2100Z: Solar activity remained at high levels. Region 9415 (S23W19) produced a long-duration X2/3b parallel-ribbon flare at 10/0526 UTC. This flare was associated with a 4000 SFU Tenflare, Type II and IV radio sweeps, a 14-degree filament disappearance, and a fast full-halo CME. Region 9415 showed decay in its trailer spots, but maintained a strong magnetic delta configuration in its leader portion, where a minor increase in spots was noted. Minor growth occurred in Region 9417 (S08W39). It produced a C6/Sf at 10/1451 UTC. Minor growth was also observed in Region 9425 (S25W49). The remaining regions were simply-structured and stable. No new regions were assigned. IB. Solar Activity Forecast: Solar activity is expected to be at moderate to high levels. Region 9415 is expected to produce another major flare during the period. IIA. Geophysical Activity Summary 09/2100Z to 10/2100Z: Geomagnetic field activity ranged from quiet to active levels. A greater than 10 MeV proton event followed today's X2/3b flare. It began at 10/0850 UTC and was in progress as the period ended. The greater than 10 MeV proton flux was near 100 PFU at the close of the period and gradually increasing. A greater than 100 MeV proton flux enhancement was also associated with the X2/3b flare. A polar cap absorption (PCA) event began around 10/1200 UTC and continued as the period ended. Thus far, maximum absorption associated with the PCA event has been estimated at 8.5 dB. The greater than 2 MeV electron flux reached high levels during the period. IIB. Geophysical Activity Forecast: A major geomagnetic storm is expected during 11 - 12 April in response to halo-CMEs observed on 09 - 10 April. Active to major storm levels are expected during this disturbance with brief severe storm levels possible at high latitudes. Unsettled to minor storm levels are expected on 13 April as the storm subsides. The greater than 10 MeV proton event is expected to continue through most of the period. The PCA event is expected to end during the latter half of the period. The greater than 2 MeV electron flux is expected to be at moderate to high levels during the period. III. Event Probabilities 11 Apr-13 Apr Class M 80/80/80 Class X 25/25/25 Proton 90/80/25 PCAF In Progress IV. Penticton 10.7 cm Flux Observed 10 Apr 170 Predicted 11 Apr-13 Apr 165/165/160 90 Day Mean 10 Apr 167 V. Geomagnetic A Indices Observed Afr/Ap 09 Apr 017/019 Estimated Afr/Ap 10 Apr 013/009 Predicted Afr/Ap 11 Apr-13 Apr 050/040-050/090-020/030 VI. Geomagnetic Activity Probabilities 11 Apr-13 Apr A. Middle Latitudes Active 15/15/35 Minor storm 25/25/15 Major-severe storm 45/45/10 B. High Latitudes Active 15/25/35 Minor storm 30/30/20 Major-severe storm 50/35/15