Positive Polarity Coronal Hole High-Speed Stream Sparks Geomagnetic Storm
A positive polarity coronal hole high-speed stream (CH HSS) is affecting our planet since late December 27, sparking G1 – Minor geomagnetic storm. Periods of active conditions are likely through December 29 followed by quiet to unsettled activity on December 30 under waning CH HSS influence.
Solar wind parameters became enhanced after 18:00 UTC on December 27 due to the influence of a positive polarity CH HSS. Solar wind speeds reached a peak of around 625 km/s just before 10:00 UTC, December 28 and periods of southward Bz were observed between 20:00 UTC, December 27 and 06:00 UTC, December 28. The parameters are expected to remain enhanced on December 28, 29 and 30.
The greater than 2 MeV electron flux was at normal levels and the greater than 10 MeV proton flux was at background levels. The greater than 2 MeV electron flux is expected to be at normal to moderate levels on through December 30 and the greater than 10 MeV proton flux is expected to persist at background levels throughout the forecast period.
Active and isolated G1 – Minor geomagnetic storm conditions were observed over the past 24 in response to (+)CH HSS influence. Geomagnetic K-index of 5 (G1 – Minor geomagnetic storm) threshold was reached at 08:59 UTC on December 28.
Periods of active conditions are likely for the remainder of December 28 through 29 due to continued CH HSS influence. Quiet to unsettled activity is expected on December 30 under waning CH HSS influence.
Solar activity was very low and the solar disk remains spotless. This year has seen a total of 218 spotless days (60%). In 2017, we had 104 spotless days (28%) and in 2016 32 days (9%).
SWPC Alerts, Warnings and Watches
Space Weather Message Code: ALTK05
Serial Number: 1254
Issue Time: 2018 Dec 28 0900 UTC
ALERT: Geomagnetic K-index of 5
Threshold Reached: 2018 Dec 28 0859 UTC
Synoptic Period: 0600-0900 UTC
Active Warning: Yes
NOAA Scale: G1 – Minor
NOAA Space Weather Scale descriptions can be found at
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.