:Product: 20010428RSGA.txt :Issued: 2001 Apr 28 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 118 Issued at 2200Z on 28 Apr 2001 IA. Analysis of Solar Active Regions and Activity from 27/2100Z to 28/2100Z: Solar activity dropped to low levels. Region 9433 (N17W50) produced isolated C-class flares, the largest of which was a C7/1f at 28/0934 UTC. Gradual decay continued in the leading and intermediate portions of this region. However, no decay was evident within its trailing spots, where a strong magnetic delta configuration remained. Region 9441 (N07E23) continued a gradual growth phase that began on 27 April, but the region remained a moderate-sized, simply-structured bipole. New Regions 9444 (S11E67) and 9445 (N23E76) were assigned. IB. Solar Activity Forecast: Solar activity is expected to be at moderate to high levels. Region 9433 is expected to produce isolated M-class flares. This region could also produce an isolated major flare during the period. IIA. Geophysical Activity Summary 27/2100Z to 28/2100Z: Geomagnetic field activity ranged from quiet to minor storm levels. An interplanetary shock at the leading edge of a CME passed the ACE spacecraft at 28/0432 UTC, followed by a sudden impulse (SI) at 28/0520 UTC (76 nT, as measured by the Boulder USGS magnetometer). The source for the CME was an M7/2b flare on 26 April. Field activity increased to unsettled to minor storm levels following the SI. The greater than 10 MeV proton flux at geosynchronous orbit briefly crossed event threshold in response to the shock passage. The greater than 10 MeV event began at 28/0430 UTC, reached a maximum of 57 PFU at 28/0500 UTC, then ended at 28/0520 UTC. Proton fluxes had decreased to near background levels by the close of the period. IIB. Geophysical Activity Forecast: Geomagnetic field activity is expected to be at unsettled to active levels through midday, 29 April as the disturbance gradually subsides. Quiet to unsettled levels are expected for the remainder of the period. Region 9433 could produce another proton flare before it crosses the west limb on 02 May. The greater than 2 MeV electron flux at geosynchronous orbit may reach high levels during the first half of the period. III. Event Probabilities 29 Apr-01 May Class M 75/75/75 Class X 20/20/20 Proton 20/20/20 PCAF yellow IV. Penticton 10.7 cm Flux Observed 28 Apr 188 Predicted 29 Apr-01 May 185/180/175 90 Day Mean 28 Apr 167 V. Geomagnetic A Indices Observed Afr/Ap 27 Apr 003/006 Estimated Afr/Ap 28 Apr 026/028 Predicted Afr/Ap 29 Apr-01 May 015/015-012/010-010/010 VI. Geomagnetic Activity Probabilities 29 Apr-01 May A. Middle Latitudes Active 30/25/20 Minor storm 15/10/10 Major-severe storm 10/05/01 B. High Latitudes Active 35/30/25 Minor storm 20/15/10 Major-severe storm 15/10/05