Negative polarity CH HSS sparks G1 – Minor geomagnetic storming


An isolated interval of G1 – Minor geomagnetic storm conditions was observed early February 19, 2018, due to the influence of negative polarity coronal hole high speed stream (CH HSS).

Solar activity over the past 24 hours was at very low levels. Earth-facing side of the Sun is spotless once again and there were no Earth-directed coronal mass ejections observed in available satellite imagery.

The greater than 2 MeV electron flux was at normal to high levels (peak flux of 2 795 pfu at 17:50 UTC, February 18) due to the influence of a negative polarity CH HSS while the greater than 10 MeV proton flux remained at background levels.

Geoeffective coronal hole February 15, 2018

Solar wind parameters indicated persistent, negative polarity CH HSS influence. Solar wind speed was at approximately 550 km/s around 12:30 UTC, February 18, peaked at 648 km/s at 03:53 UTC today and dropped back to approximately 550 km/s around 12:30 UTC today. Total field achieved a maximum value of 7 nT while the Bz component was variable between +/-5 nT. Phi angle remained in a predominantly negative sector.

The geomagnetic field was at quiet to active levels with an isolated period of G1 – Minor storm conditions caused by negative polarity CH HSS.

Estimated planetary k-index February 19, 2018

G1 threshold was reached 02:59 UTC today. Under G1 conditions, area of impact is primarily poleward of 60 degrees Geomagnetic Latitude. Weak power grid fluctuations can occur, minor impact on satellite operations is possible and aurora may be visible at high latitudes.

The geomagnetic field is expected to be at quiet to isolated active levels through February 20 followed by quiet to unsettled levels on February 21 due to persistent CH HSS influence.

Solar activity is expected to be at very low levels over the next three days and the greater than 2 MeV electron flux at moderate to high levels.

Featured image credit: NOAA/SWPC


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