G1 (Minor) geomagnetic storm in progress

NOAA/SWPC issued G1 (Minor) geomagnetic storm alert early on December 7 due to the high speed solar wind stream originating from a geoeffective coronal hole in the Sun's southern hemisphere.

Geomagnetic K-index of 5 (G1 – Minor) threshold was reached at 01:24 UTC today.

Space Weather Message Code: ALTK05
Serial Number: 757
Issue Time: 2014 Dec 07 0125 UTC

ALERT: Geomagnetic K-index of 5
Threshold Reached: 2014 Dec 07 0124 UTC
Synoptic Period: 0000-0300 UTC
Active Warning: Yes
NOAA Scale: G1 - Minor
Potential Impacts: Area of impact primarily poleward of 60 degrees Geomagnetic Latitude.
Induced Currents - Weak power grid fluctuations can occur.
Spacecraft - Minor impact on satellite operations possible.
Aurora - Aurora may be visible at high latitudes, i.e., northern tier of the U.S. such as northern Michigan and Maine.

Observations at the ACE spacecraft during the last 24 hours suggested the arrival of the negative polarity south polar coronal hole high speed solar wind stream. 

Wind speed began rising after 14:00 UTC on December 6, reaching a maximum of 788 km/s by 22:06 UTC. Bt began rising after 02:00 UTC, reaching a maximum of 25 nT at 14:30 UTC.  Bz was mostly neutral or positive until approximately 18:00 UTC after which it became negative, dipping to -14 nT at 18:26 UTC.  Phi angle switched from a positive (away) to a negative (toward) sector around 06/03:20 UTC.

The geomagnetic field is expected to be disturbed by the high speed solar wind stream for the next three days. Unsettled to active levels are likely, with a slight chance for an isolated minor storm period.

Image credit: SWPC/NOAA

Aurora watchers can expect great sky display around the polar circles.

Featured image credit: SWPC/NOAA