NOAA forecasters have issued a geomagnetic storm warning for Sept. 12th when a CME, coronal mass ejection, is expected to deliver a glancing but potent blow to Earth’s magnetic field. The storm could reach moderate intensity (G2-class) with auroras visible across northern-tier US states such as Maine, Michigan, and Minnnesota.
Yesterday, the magnetic canopy of sunspot AR2158 erupted, producing an explosion that lasted more than 6 hours. The flare peaked on Sept. 9th at 00:30 UT with a classification of M4 on the Richter Scale of Solar Flares. Long-duration flares tend to produce bright CMEs, and this one was no exception. Coronagraphs onboard the Solar and Heliospheric Observatory observed a CME racing out of the blast site at nearly 1,000 km/s (2.2 million mph)
Radio frequency disruption could occur as well as increase seismic activity as well as volcanic activity could increase.
Most of the storm cloud is heading north of the sun-Earth line, but not all. A fraction of the CME will deliver a glancing blow to Earth’s magnetic field during the early hours of Sept. 12th. In the past few weeks, glancing blows from minor CMEs have sparked beautiful auroras around the Arctic Circle. This CME could spark even better displays. NOAA forecasters estimate a 79% (not a typo: 79%) chance of polar geomagnetic storming on Sept. 12th.