Disturbed geomagnetic field: Brief G2 – Moderate geomagnetic storm

Earth's magnetic field is still disturbed in response to continued presence of a positive polarity coronal hole high speed stream (CH HSS), possibly combined with a transient feature originally expected for May 17.  

Between 12:30 UTC on May 18 and 12:30 UTC on May 19, Bt increased from near 5nT to near a peak of 17nT. Bz fluctuated between positive and negative, with deflections to near -16nT. Solar wind velocity started rising after 16:00 UTC on May 18 and eventually reached 560 km/s at 10:00 UTC on May 19. 

Geomagnetic K-Index of 6 (G2 – Moderate geomagnetic storm) threshold was reached at 02:59 UTC on May 19, and lasted for a few hours. Area of impact was primarily poleward of 55 degrees Geomagnetic Latitude.

Under G2 conditions, power grid fluctuations can occur. High-latitude power systems may experience voltage alarms. Satellite orientation irregularities may occur; increased drag on low Earth-orbit satellites is possible. HF (high frequency) radio propagation can fade at higher latitudes and aurora may be seen as low as New York to Wisconsin to Washington state.

The greater than 2 MeV electron flux was at normal background levels, during last 24 hours. The greater than 10 MeV proton flux remained at background levels.

The greater than 2 MeV electron flux is expected to persist at normal background levels on May 19 and 20 in response to the onset of coronal hole high speed stream (CH HSS) or possible glancing blow CME effects.

An increase to moderate or high levels is expected on May 21, with a delayed response to the elevated solar wind. The greater than 10 MeV proton flux is expected to remain below S1 (Minor).

ALERT: Geomagnetic K-index of 6

Threshold Reached: 2015 May 19 0259 UTC
Synoptic Period: 0000-0300 UTC
 
Active Warning: Yes
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.

Geomagnetic field forecast

Mostly quiet levels are expected on May 20 and 21 as the high speed wind stream begins to stabilize then wane, SWPC said in their Forecast Discussion issued 12:30 UTC today.

Featured image credit: NOAA/SWPC