"Earlier, it was stated that the current Solar Radiation Storm was the largest since May 2005," an announcement from a National Oceanographic and Atmospheric Administration division said.
"After the arrival of the CME [coronal mass ejection] earlier today ... this is now the largest Solar Radiation Storm since October 2003 (The Halloween Storms)," NOAA's Space Weather Prediction Center said on its Facebook page.
On Sunday, a cluster of sunspots in an active region of the sun blasted a bubble of energized plasma -- composed mainly of high-energy protons -- in the general direction of Earth.
The blast -- known as a coronal mass ejection -- interacted with the Earth's magnetosphere beginning Tuesday, sparking a global geomagnetic storm.
Such storm can cause problems with satellite operation and radio communications, experts said.
"High latitude [radio] communications can be impacted," NASA solar physicist C. Alex Young told Discovery News.
"I have heard from colleagues that airlines have already had to reroute polar flights for up to two days because of communication blackouts at the poles."