Partial-halo CME impact sparks G1 geomagnetic storm


A partial-halo coronal mass ejection (CME) produced on June 28, 2017 hit Earth's magnetic field at 17:12 UTC on July 1, almost 24 hours earlier than expected. The impact was weak but managed to spark a G1 – Minor geomagnetic storm 17 hours later. G1 Watch conditions remain in effect for July 2 – 3.

Geomagnetic K-index of 5 (G1 geomagnetic storm) threshold was reached at 08:59 UTC on July 2. Under G1 conditions, the 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.

Partial-halo CME produced on June 28, 2017. Credit: ESA/NASA LASCO C2

Transient-based enhancements in the solar wind are expected to continue through the rest of the day with further enhancement from the June 28 CME expected through July 3.

A waning CME influence will likely transition into weak enhancements from a small, negative polarity coronal hole high speed stream (CH HSS) on July 4.

Estimated planetary K index (3 hour data) - July 2, 2017

Space Weather Message Code: SUMSUD
Serial Number: 221
Issue Time: 2017 Jul 01 1735 UTC

SUMMARY: Geomagnetic Sudden Impulse
Observed: 2017 Jul 01 1712 UTC
Deviation: 20 nT
Station: CMO

Space Weather Message Code: ALTK05
Serial Number: 1119
Issue Time: 2017 Jul 02 0900 UTC


ALERT: Geomagnetic K-index of 5
Threshold Reached: 2017 Jul 02 0859 UTC
Synoptic Period: 0600-0900 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.

Featured image: Partial-halo CME produced on June 28, 2017. Credit: ESA/NASA LASCO C2

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