CME impact detected, G3 - Strong geomagnetic storm watch remains but confidence diminishing

CME impact detected, G3 - Strong geomagnetic storm watch remains but confidence diminishing

A geomagnetic sudden impulse -- CME produced by a long-duration C7.4 solar flare on December 7, was observed at DSCOVR satellite at the L1 point at 01:32 UTC on December 10.

The total field reached 16 nT while wind speeds topped out near 571 km/s, producing a period of active geomagnetic conditions.

The G3 - Strong and G2 - Moderate geomagnetic storm watches for December 10 and 11, respectively, remain in place at this time. 

However, confidence in storming reaching those levels is diminishing, SWPC forecasters said.

Solar wind parameters were mostly at background levels in 24 hours to 00:30 UTC on December 10. Possibly reflecting some weak coronal hole influence (-) out ahead of the anticipated CME.

Total field values began averaging between 5 - 8 nT and the Bz component underwent a sustained deflection of -5 nT before oscillating between +/- 5 nT.

However, wind speeds have remained at ambient-like levels averaging 350 km/s before increasing to 450 km/s by 00:30 UTC.

Phi was predominantly in a negative solar sector while undergoing brief excursions into a positive orientation.

ACE EPAM particles continue to rise, suggesting the CME is still coming toward the magnetosphere protecting Earth.

Space Weather Message Code: SUMSUD
Serial Number: 226
Issue Time: 2020 Dec 10 0447 UTC

SUMMARY: Geomagnetic Sudden Impulse
Observed: 2020 Dec 10 0211 UTC
Deviation: 30 nT
Station: BOU

NOAA Space Weather Scale descriptions can be found at
www.swpc.noaa.gov/noaa-scales-explanation

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Space Weather Message Code: ALTK04
Serial Number: 2180
Issue Time: 2020 Dec 10 0300 UTC

ALERT: Geomagnetic K-index of 4
Threshold Reached: 2020 Dec 10 0259 UTC
Synoptic Period: 0000-0300 UTC

Active Warning: Yes

NOAA Space Weather Scale descriptions can be found at
www.swpc.noaa.gov/noaa-scales-explanation

Potential Impacts: Area of impact primarily poleward of 65 degrees Geomagnetic Latitude.
Induced Currents - Weak power grid fluctuations can occur.
Aurora - Aurora may be visible at high latitudes such as Canada and Alaska.

Featured image: Aurora forecast model at 04:46 UTC on December 10, 2020. Credit: SWPC

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