Earth enters a stream of fast-moving solar wind, G2 – Moderate Geomagnetic Storm Watch in effect


Our planet has entered a stream of fast-moving solar wind flowing from a large positive polarity coronal hole. A G1 – Minor Geomagnetic Storm Watch is in effect for August 31 and G2 – Moderate for September 1.

Solar wind parameters reflected a slow regime through midday, August 30. Just after 12:00 UTC, a solar sector boundary crossing was observed, with phi angle rotating into a positive orientation.

Simultaneously, total field strength increased from 5 nT to 12 nT, the Bz component deflected from 2 nT to -3 nT, and solar wind speeds increased from around 380 km/s to near 430 km/s.

Wind speeds continued to increase and reached a peak speed of 600 km/s by 00:30 UTC today, and the Bz component saw a maximum southward deflection to -8 nT.

These enhanced parameters indicated an early arrival of the anticipated CIR in advance of the positive polarity Coronal Hole High Spead Stream CH HSS.

Solar wind parameters are expected to reflect continued enhanced levels on August 31 – September 1. Solar wind speed is expected to reach upwards of 650 km/s based on STEREO-A PLASTIC data, and continue into September 1.

Conditions are expected to remain slightly elevated on September 2, but begin a gradual decrease by the end of September 3.

The geomagnetic field is expected to be at unsettled to active levels, with isolated G1 – Minor storm conditions likely on August 31, due to CH HSS onset.

CH HSS influence is expected to persist through the beginning of September 1, with periods of G1 to G2 (Minor to Moderate) storm conditions likely early in the period.

Late on September 2, conditions are expected to taper off as CH HSS effects begin to wane.

Geomagnetic K-index of 5 (G1 – Minor geomagnetic storm) threshold was reached at 05:46 UTC.

Space Weather Message Code: ALTK05
Serial Number: 1272
Issue Time: 2019 Aug 31 0549 UTC

ALERT: Geomagnetic K-index of 5
Threshold Reached: 2019 Aug 31 0546 UTC
Synoptic Period: 0300-0600 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.

"The last time this stream hit Earth's magnetic field, almost a month ago, auroras were observed in multiple northern-tier US states. It could happen again this weekend," said Dr. Tony Phillips of SpaceWeather.com.

Featured image credit: NOAA/SWPC

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