Solar activity from numbered regions on the visible disk was low. Impulsive B- and C-class flares were observed throughout the period, the largest being an optically uncorrelated C3 flare at 16/0957 UTC. However, the most impressive activity of the day was a remarkable backside CME, observed on SOHO/LASCO starting at about 15/2355 UTC. This event resulted in the proton enhancements discussed in section IIA below. The observed CME together with backside imagery inferred from the SOHO/MDI instrument suggest old Region 9557 (S20, L=283) as the likely source, presently located near the far backside central meridian. On the visible disk, three new regions were numbered today: 9583 (S23E13), 9584 (S11E60), and 9585 (N15E74). All appear to be small, simply structured beta-class groups with low flare activity potential.

Solar activity on the visible disk is expected to persist at mainly low levels for the next three days.

Geomagnetic field activity has been quiet to unsettled throughout the period. A major proton event for >= 100MeV protons above 1pfu began at 16/0105 UTC, followed by >= 10Mev protons above 10pfu at 16/0135 UTC. Maximum flux for 100Mev protons was 29pfu at 16/0305 UTC, and for 10MeV protons was 493pfu at 16/0355 UTC. Both events remain in progress, and represent a record response for a presumed CME source so far behind the western limb as described in section 1A above. Greater than 2MeV electrons were observed at moderate enhancement levels again today, although the electron sensor on GOES-8 was saturated by the proton event for much of the period.

The geomagnetic field is expected to be at active to minor storm levels within 24 hours, in response to anticipated shock passage from CME activity reported on August 14th. Isolated major storm periods may also be possible at higher latitudes, as well as an enhancement of 10MeV proton levels for the event in progress. Geomagnetic storm activity is expected to wane during day two, along with the 100MeV proton event. The 10MeV proton event is expected to persist at levels above 10pfu into day three. Greater than 2MeV electrons are also expected to persist at moderate enhancement levels.

  Observed       16 Aug 143
  Predicted   17 Aug-19 Aug  140/140/145
  90 Day Mean        16 Aug 151

  Observed Afr/Ap 15 Aug  004/009
  Estimated     Afr/Ap 16 Aug  007/008
  Predicted    Afr/Ap 17 Aug-19 Aug  025/020-017/015-012/018