Earth is now under the influence of a stronger than expected coronal hole high speed stream (CH HSS). G2 (Moderate) geomagnetic storming has been observed and continued low-level storming is possible over the next 24 hours as Earth remains under the influence of this high speed solar wind.
In last 24 hours (- 12:30 UTC on December 7) solar wind conditions indicated the onset of a co-rotating interaction region (CIR) followed by CH HSS and possible transient influence from the CME on December 5.
The period began at nominal levels with solar wind speeds in the 320 to 350 range and total field measurements between 1 nT and 6 nT. By approximately 21:14 UTC on December 7, a slow increase in total field, solar wind speed, temperature, and density was observed culminating in a total field increase of 27 nT at 02:19 UTC on December 8. The Bz component went southward to a maximum of -23 nT while solar wind speeds were near 500 km/s as the CIR reached its maximum strength. Solar wind speed continued near 500 km/s until a reverse shock occurred at 07:30 UTC on December 8.
Solar wind speed increased again to a maximum of 651 km/s with total field suddenly decreasing from 10 nT to 5 nT. The reverse shock could either be related to the CIR or the glancing blow that was expected from the 05 Dec CME. Phi angle was variable through the period until approximately 06:10 UTC on December 8 when it moved into a mostly positive (away) sector. (SWPC)
Geomagnetic K-index of 4 threshold was reached at 01:21 UTC on December 8, K-index of 5 (G1) at 01:58 UTC.
At 02:17 UTC geomagnetic storming reached G2 levels. Area of impact was primarily poleward of 55 degrees Geomagnetic Latitude. At those levels high-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage. HF radio propagation can fade at higher latitudes.
At 04:30 UTC observed K-index was back at 5 (G1). The estimated planetary K-index at 09:00 UTC was 4.
High-latitude sky watchers should be alert for auroras.
Click on the image (or here) for latest data.
Space Weather Message Code: ALTK06
Serial Number: 314
Issue Time: 2013 Dec 08 0224 UTC
ALERT: Geomagnetic K-index of 6
Threshold Reached: 2013 Dec 08 0217 UTC
Synoptic Period: 0000-0300 UTC
Active Warning: Yes
NOAA Scale: G2 – Moderate
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.
The geomagnetic field is expected to be at quiet to active levels with a chance for Minor storm (G1-Minor) periods for the rest of the UTC day on December 8 due to continued CH HSS effects. Quiet to active levels with a slight chance for isolated minor storm (G1-Minor) periods are expected on December 9 – 10 due to combined CH HSS and CME effects.
Featured image: NOAA/SWPC
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