Viewing archive of Saturday, 17 September 2011

Solar activity report

Report of Solar-Geophysical Activity 2011 Sep 17 2200 UTC
Prepared by the NOAA © SWPC and processed by

Joint USAF/NOAA Report of Solar and Geophysical Activity

SDF Number 260 Issued at 2200Z on 17 Sep 2011

IA. Analysis of Solar Active Regions and Activity from 16-2100Z to 17-2100Z

Solar activity was low during the past 24 hours. Regions 1289 (N22W67) and 1290 (S13W84) each produced C-class events, the largest a long duration C2 event from Region 1289 at 16/2351Z. An associated CME first became visible on LASCO C2 imagery at 16/2348Z and had an estimated plane-of-sky speed of 575 km/s. Further analysis will be conducted to determine geoeffectiveness.
IB. Solar Activity Forecast
Solar activity is expected to be low with a chance for isolated M-class flares for the next three days (18-20 September).
IIA. Geophysical Activity Summary 16-2100Z to 17-2100Z
The geomagnetic field was quiet until approximately 17/0400Z when effects from the 14 September CME arrived at Earth. A shock was observed at ACE at 17/0256Z which was followed by a sudden impulse of 21 nT observed by the Boulder magnetometer. Solar wind speeds increased from approximately 350 km/s to 450 km/s along with a noticeable increase in temperature and density. The interplanetary magnetic field Bt reached +14 nT and there were several extended periods of southward Bz with a maximum deviation of -12 nT. Conditions at Earth increased to active levels following shock arrival with an isolated minor storm period at 17/1800Z. Solar wind speeds peaked at 550 km/s around 17/1115Z but have since decreased to approximately 450 km/s. The greater than 2 MeV electron flux at geosynchronous orbit reached high levels during the period.
IIB. Geophysical Activity Forecast
The geomagnetic field is expected to be quiet to unsettled with a slight chance for isolated active periods on day one (18 September) as effects from the 14 September CME subside. Mostly quiet conditions are expected for days two and three (19-20 September).
III. Event Probabilities 18 Sep to 20 Sep
Class M30%35%35%
Class X01%01%01%
IV. Penticton 10.7 cm Flux
  Observed       17 Sep 145
  Predicted   18 Sep-20 Sep  145/145/145
  90 Day Mean        17 Sep 102
V. Geomagnetic A Indices
  Observed Afr/Ap 16 Sep  002/002
  Estimated     Afr/Ap 17 Sep  023/032
  Predicted    Afr/Ap 18 Sep-20 Sep  010/010-005/005-005/005
VI. Geomagnetic Activity Probabilities 18 Sep to 20 Sep
A. Middle Latitudes
Minor storm10%01%01%
Major-severe storm01%01%01%
B. High Latitudes
Minor storm15%05%01%
Major-severe storm01%01%01%

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