A G3 – Strong geomagnetic storm was recorded late on March 20 into early March 21, following the arrival of a coronal mass ejection (CME) that left the Sun on March 18, according to the NOAA Space Weather Prediction Center (SWPC).
Solar wind observations show at least two CME structures arrived at Earth, with the first detected around 01:32 UTC on March 20 and the second near 20:18 UTC the same day. Solar wind speeds increased to approximately 567 km/s, while the total interplanetary magnetic field reached 36 nT.
The southward component of the magnetic field (Bz) dropped to −28 nT — a configuration that enables efficient coupling between the solar wind and Earth’s magnetic field.
This combination of elevated solar wind speed and sustained southward Bz drove geomagnetic activity into the G3 – Strong range. Under such conditions, space-based systems may experience increased atmospheric drag, while high-frequency (HF) radio communication and satellite navigation systems can be degraded. Power systems at higher latitudes may require operational adjustments to maintain grid stability.
Forecast guidance from SWPC indicates that geomagnetic activity is expected to gradually decrease as CME effects weaken through March 22. However, additional disturbances are anticipated as a coronal hole high-speed stream (CH HSS) begins to influence the solar wind environment, potentially sustaining G1 – Minor conditions into March 22 and maintaining unsettled to active conditions on March 23.
The timing of this event coincides with the March equinox period, when geomagnetic coupling efficiency is typically enhanced due to seasonal alignment between Earth’s magnetic field and the interplanetary magnetic field. This seasonal factor can contribute to stronger geomagnetic responses even when solar input is moderate.
NOAA SWPC classifications define G3 storms as capable of causing operational impacts to satellites, navigation systems, and power infrastructure at high latitudes, while also expanding auroral visibility to mid-latitude regions.
Solar activity remained at very low levels over the past 24 hours, with only two numbered sunspot regions present on the solar disk, both exhibiting limited development and no significant flare production.
A full halo coronal mass ejection (CME) was observed beginning at 13:36 UTC on March 20. However, analysis indicates this event originated from the far side of the Sun and is not Earth-directed.
Solar activity is expected to remain low through March 23, with only isolated C-class flares likely.
References:
1 Forecast Discussion – NOAA/SWPC – Issued at 00:30 UTC on March 21, 2026