:Product: 20010817RSGA.txt :Issued: 2001 Aug 17 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 229 Issued at 2200Z on 17 Aug 2001 IA. Analysis of Solar Active Regions and Activity from 16/2100Z to 17/2100Z: Solar activity was low. Only a few low-level C-class subflares occurred. The largest was a C1/Sf at 17/0011 UTC in Region 9581 (S25W42). Although there are several sunspot groups on the visible disk all of them are relatively small and magnetically simple. New Regions 9586 (S15W47) and 9587 (S11E56) were numbered. IB. Solar Activity Forecast: Solar activity is expected to be low. Additional low-level C-class flares are possible. IIA. Geophysical Activity Summary 16/2100Z to 17/2100Z: The geomagnetic field was quiet until the occurrence of a sudden impulse observed at ground magnetometers (36 nT at Boulder) at about 17/1103 UTC. The impulse was preceded by a shock observed at the NASA ACE spacecraft at 17/1017 UTC. The geomagnetic field has been at mostly active to minor storm levels since the impulse. A series of magnetopause crossings were observed at the NOAA GOES spacecraft in the interval from about 17/1930--2100 UTC. The greater than 100 MeV proton event which began yesterday has ended (start 16/0105 UTC, 29 pfu peak at 16/0305 UTC, and end 17/1415 UTC). The greater than 10 MeV event remains in progress (start 16/0135 UTC and 493 pfu peak at 16/0355 UTC). The current proton flux (17/2100 UTC) at greater than 10 MeV is about 20 pfu and is slowly decaying. IIB. Geophysical Activity Forecast: The geomagnetic field is expected to be at mostly active to minor storm levels for the next 24 hours becoming unsettled to active after that. The greater than 10 MeV proton event is expected to end by 19 August. III. Event Probabilities 18 Aug-20 Aug Class M 10/10/10 Class X 01/01/01 Proton 90/30/01 PCAF in progress IV. Penticton 10.7 cm Flux Observed 17 Aug 145 Predicted 18 Aug-20 Aug 150/150/155 90 Day Mean 17 Aug 151 V. Geomagnetic A Indices Observed Afr/Ap 16 Aug 003/008 Estimated Afr/Ap 17 Aug 025/025 Predicted Afr/Ap 18 Aug-20 Aug 020/015-015/015-010/018 VI. Geomagnetic Activity Probabilities 18 Aug-20 Aug A. Middle Latitudes Active 30/20/15 Minor storm 15/05/05 Major-severe storm 05/01/01 B. High Latitudes Active 40/30/20 Minor storm 20/10/05 Major-severe storm 05/01/01