Solar Flare Causes March 29 Radio Blackout, Minor Geomagnetic Storm Expected April 2


NOAA’s Space Weather Prediction Center (SWPC) has reported that a brief radio blackout “event” occurred on March 29 at 1748 UTC, the result of an “impulsive” or short-lived R3 (strong) solar flare. Extreme ultraviolet radiation from the X-1 class event “sent waves of ionization rippling through Earth’s upper atmosphere and disturbed the normal propagation of terrestrial radio transmissions,”’s Tony Phillips reported. The site noted that radio engineer Stan Nelson, KB5VL, of Roswell, New Mexico, was monitoring WWV at 20 MHz “when the signal wobbled then disappeared entirely for several minutes.”

“The Doppler shift of the WWV signal (the ‘wobble’ just before the blackout) was nearly 12 Hz, the most I have ever seen,” Nelson said. said the flare not only caused a radio blackout but generated signals of its own.

“The explosion above sunspot AR2017 sent shock waves racing through the Sun’s atmosphere at speeds as high as 4800 km/s (11 million mph),” reported. “Radio emissions stimulated by those shocks crossed the 93 million mile divide to Earth, causing shortwave radio receivers to roar with static.” said “strong bursts” were detected at frequencies as high as 2800 MHz. “It was a very broad band event,” Phillips concluded.

G1 (minor) geomagnetic storming is expected on April 2 from several coronal mass ejections (CMEs), including the one from the March 29 event. Observers say that none of the incoming CMEs is directed right at Earth, but Phillips said that the “series of glancing blows…will rattle Earth’s magnetic field and possibly spark auroras.”

NOAA forecasters estimate a 60 percent chance of a “major-severe” storm on April 2 in the higher latitudes, with chances in the 30 percent range for April 1 and 3. The CMEs’ effects will be far less noticeable at middle latitudes, with the chance of a major-severe geomagnetic storm no greater than 5 percent for the next three days.

On March 31 at 2200 UTC, the SWPC’s Solar Geophysical Activity Report and Forecast described solar activity as “moderate” for the past 24 hours. “The largest solar event of the period was an M1 event,” which occurred on March 31 at 0907 UTC. The SWPC said there is only a slight chance for an X-class flare from April 1 through April 3.

“The geomagnetic field has been at quiet to unsettled levels for the past 24 hours,” the report continued. “The geomagnetic field is expected to be at quiet to active levels” April 1-3, with “unsettled to minor storm levels” on April 2.

The largest flare of Solar Cycle 24 occurred on April 9, 2011 — an X-6.9 event. As NOAA explains, “Large X-ray bursts cause shortwave fades for HF propagation paths through the sunlit hemisphere. Some large flares are accompanied by strong solar radio bursts that may interfere with satellite downlinks.”