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.
Featured image credit: NOAA/SWPC