Viewing archive of Wednesday, 11 April 2001

Solar activity report

Report of Solar-Geophysical Activity 2001 Apr 11 2200 UTC
Prepared by the NOAA © SWPC and processed by

Joint USAF/NOAA Report of Solar and Geophysical Activity

SDF Number 101 Issued at 2200Z on 11 Apr 2001

IA. Analysis of Solar Active Regions and Activity from 10-2100Z to 11-2100Z

Solar activity was moderate. A single M-class event occurred during the period. Region 9415 (S22W27) produced an M2/1f parallel ribbon flare at 11/1326 UTC. This event was accompanied by Type II and IV radio sweeps, a 540 sfu 10 cm radio burst, and a full-halo coronal mass ejection (CME). Two new regions were numbered: 9426 (S09E40) and 9427 (S07W12).
IB. Solar Activity Forecast
Solar activity is expected to be at moderate to high levels. Region 9415 can be expected to produce another major flare during the period.
IIA. Geophysical Activity Summary 10-2100Z to 11-2100Z
The geomagnetic field ranged from quiet to severe storm levels. Two discernable shocks were detected by the ACE spacecraft at approximately 11/1300 and 11/1520 UTC. These effects were most likely the precursors for the two earth-directed CME's produced on 9-10 April. The resulting CME's arrival at earth produced severe geomagnetic storming during the period of 11/1500-1800 UTC. The greater than 10 MeV proton flux was at high levels all period long, reaching a maximum of 322 PFU near the end of the period. A polar cap absorption (PCA) event remained in effect during the period. The greater than 2 MeV electron flux has at high levels for the first part of the period and then decreased to moderate levels for the remainder of the period.
IIB. Geophysical Activity Forecast
The geomagnetic field is expected to continue at active to major storm levels during the first day of the period. A second geomagnetic storm is expected to arrive late on 12 April or early on 13 April UTC. This disturbance will be the result of the full-halo CME described in Section 1A. Brief severe storm levels at high latitudes can be expected. Unsettled to minor storm levels are expected on 14 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 mostly moderate levels during the period.
III. Event Probabilities 12 Apr to 14 Apr
Class M80%80%80%
Class X25%25%25%
PCAFin progress
IV. Penticton 10.7 cm Flux
  Observed       11 Apr 160
  Predicted   12 Apr-14 Apr  160/160/155
  90 Day Mean        11 Apr 167
V. Geomagnetic A Indices
  Observed Afr/Ap 10 Apr  007/009
  Estimated     Afr/Ap 11 Apr  050/060
  Predicted    Afr/Ap 12 Apr-14 Apr  060/090-050/050-020/025
VI. Geomagnetic Activity Probabilities 12 Apr to 14 Apr
A. Middle Latitudes
Minor storm25%25%15%
Major-severe storm45%45%10%
B. High Latitudes
Minor storm30%30%25%
Major-severe storm50%35%15%

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