Positive polarity CH HSS sparks G1 – Minor geomagnetic storm
Image credit: NOAA/SWPC
A weak positive polarity Coronal Hole High Speed Stream (CH HSS) affecting our planet since late June 17, 2018, sparked a G1 – Minor geomagnetic storm at 02:56 UTC on June 18.
Solar wind parameters, as measured by the DSCOVR spacecraft located at the L1 point, were at near-background levels until just after 21:00 UTC on June 17 when the total field became slightly enhanced with the likely arrival of a Co-rotating Interaction Region (CIR) ahead of a weak positive polarity CH HSS.
Total magnetic field strength increased from 2-15 nT. The Bz component rotated southward to a maximum of -13 nT while solar wind speeds increased from approximately 295 to 415 km/s. Phi angle suggested the passage of a Solar Sector Boundary Crossing (SSBC) with a transition from the negative sector to the positive sector after 12:50 UTC on June 17.
The geomagnetic field responded with only quiet levels despite the slight increase in solar wind parameters towards the end of the UTC day.
Geomagnetic K-index of 5 (G1 – Minor geomagnetic storm) threshold was reached at 02:56 UTC while solar wind speed peaked at 503 km/s at 06:17 UTC, June 18.
The greater than 2 MeV electron flux ranged from normal to moderate levels over the past 24 hours, while the greater than 10 MeV proton flux remained at background levels. The greater than 2 MeV electron flux is expected to remain at normal to moderate levels while background levels are expected for the greater than 10 MeV proton flux over the next 3 days.
The geomagnetic field is expected to be at quiet to unsettled levels, with possible isolated active periods, on June 18 and 19 due to a weak solar wind enhancement from a positive polarity CH HSS. A return to mostly quiet levels is expected on June 20.
Teo Blašković founded The Watchers in 2011 and edited it until 2026, covering seismic and volcanic activity, extreme weather, space weather and near-Earth objects. Articles on this page are his archive.
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