Update just sent in by ESA’s Juha-Pekka Luntama, Head of the Space Weather segment in the Agency’s Space Situational Awareness Programme office.

The shock from the arrival of the CME (Coronal Mass Ejection) of 10 September was detected by the ACE spacecraft just before 18:00 CEST today, 12 September.

The solar wind speed increased rapidly to about 650 km/s and the total strength of the interplanetary magnetic field (IMF) rose to 28 nT. However, the z component of the IMF (Bz) was oscillating between positive and negative values limiting the geo-impact of the CME. Thus, the geomagnetic storm triggered by the arrival of the CME is currently at a moderate level. If the Bz turns more permanently negative while the plasma cloud passes the Earth, the event will become more geo-effective. There is still a possibility that the geomagnetic storm will reach a strong level on 13 September. However, it is extremely unlikely that this event would reach levels that would cause any damage in the ground based infrastructure.

The arrival of the CME also drove the >10 MeV proton flux briefly above the 100 pfu level. This is not unusual for an arrival of a shock driven by a CME. At the moment the proton flux values are already declining for all energy levels.