CH HSS sparks geomagnetic storming, G2 warning issued

Earth is under the influence of a positive polarity coronal hole high speed stream (CH HSS) which is causing geomagnetic storming. G1 – Minor geomagnetic storm threshold was first reached at 16:12 UTC on March 21, 2017. A G2 – Moderate geomagnetic storm warning was issued 20:16 UTC.

Solar wind parameters were nominal until near 03:00 UTC on March 21, after the onset of co-rotating interaction region (CIR / interaction between fast and slow streams) ahead of positive polarity CH HSS. Solar wind speeds increased from near 325 km/s to 550 km/s by 12:30 UTC. Total field strength was steady at 5 nT until the CIR caused it to increase to as high as 18 nT. The Bz component was variable and had a sustained period in southern sector between 05:45 and 06:21 UTC, reaching a maximum deflection of -17 nT

Geomagnetic K-index of 5 (G1 – Minor geomagnetic storming) threshold was first reached at 16:12 UTC and then again at 19:27 UTC.

At 20:16 UTC, a G2 – Moderate geomagnetic storm warning (valid 20:15 – 23:59 UTC) was issued due to escalating solar wind conditions.

SWPC forecasters expect the solar wind environment to remain enhanced through March 23 due to CH HSS influences. The geomagnetic field is expected to be unsettled to active, with G1-Minor storm conditions possible through March 23.

Isolated periods of G2 – Moderate storming is possible.

SWPC alerts and warnings

Space Weather Message Code: WARK06
Serial Number: 371
Issue Time: 2017 Mar 21 2016 UTC

WARNING: Geomagnetic K-Index of 6 expected
Valid From: 2017 Mar 21 2015 UTC
Valid To: 2017 Mar 21 2359 UTC
Warning Condition: Onset
NOAA Scale: G2 – Moderate

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

Potential Impacts: Area of impact primarily poleward of 55 degrees Geomagnetic Latitude.
Induced Currents – Power grid fluctuations can occur. High-latitude power systems may experience voltage alarms.
Spacecraft – Satellite orientation irregularities may occur; increased drag on low Earth-orbit satellites is possible.
Radio – HF (high frequency) radio propagation can fade at higher latitudes.
Aurora – Aurora may be seen as low as New York to Wisconsin to Washington state.

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Space Weather Message Code: WARK05
Serial Number: 1322
Issue Time: 2017 Mar 21 2016 UTC

EXTENDED WARNING: Geomagnetic K-index of 5 expected
Extension to Serial Number: 1321
Valid From: 2017 Mar 21 1608 UTC
Now Valid Until: 2017 Mar 22 0300 UTC
Warning Condition: Persistence

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

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.

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Space Weather Message Code: ALTK05
Serial Number: 1075
Issue Time: 2017 Mar 21 1928 UTC

ALERT: Geomagnetic K-index of 5
Threshold Reached: 2017 Mar 21 1927 UTC
Synoptic Period: 1800-2100 UTC

Active Warning: Yes
NOAA Scale: G1 – Minor

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

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.

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Space Weather Message Code: ALTK05
Serial Number: 1074
Issue Time: 2017 Mar 21 1614 UTC

ALERT: Geomagnetic K-index of 5
Threshold Reached: 2017 Mar 21 1612 UTC
Synoptic Period: 1500-1800 UTC

Active Warning: Yes
NOAA Scale: G1 – Minor

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

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: Geoeffective coronal hole on March 20, 2017. Credit: NASA SDO/AIA