
An isolated period of G1-Minor geomagnetic storming was observed during the 22/1800-2100 UTC synoptic period. This activity is not fully understood because wind speeds were below 400 km/s and there was no significant negative Bz observed in the solar wind data. Forecasters believe this to be a rare sub-storm related to elevated density and a sustained negative By component of the interplanetary magnetic field. The yellow line on the attached ACE data shows the Bz component and the white line shows the By component. During the geomagnetic activity Bz was clearly positive while By was negative for an extended period of time. The geomagnetic field is expected to be at unsettled to active levels for the remainder of day one (23 Jun).