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.

Solar activity is expected to be low with a chance for isolated M-class flares for the next three days (18-20 September).

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.

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).

  Observé       17 Sep 145
  Prévisionnel   18 Sep-20 Sep  145/145/145
  Moyenne des 90 derniers jours        17 Sep 102

  Observé Afr/Ap 16 Sep  002/002
  Estimé     Afr/Ap 17 Sep  023/032
  Prévisionnel    Afr/Ap 18 Sep-20 Sep  010/010-005/005-005/005