Yet Another X-Flare

Sunspot AR3664 (a.k.a. AR3697) has decayed, but it is still potent. On May 31st it emitted another X-flare (X1.1), the third this week. NASA's Solar Dynamics Observatory captured the extreme ultraviolet flash:

Radiation from the flare ionized the top of Earth's atmosphere, briefly causing a shortwave radio blackout over the Pacific side of North America. Signals below 30 MHz faded for as much as 30 minutes after the flare's peak (May 31st @ 2203 UT).

The flare, while intense, was too brief to lift a significant CME out of the sun's atmosphere. SOHO coronagraph images show no solar storm clouds heading for Earth.

What makes a decaying sunspot like AR3664 so active? This magnetic map provides the answer:

Within the sunspot's primary core, two oppositely-signed magnetic poles are crowded together, + vs. -. When this happens, magnetic recombination can cause very powerful explosions even from a sunspot that's falling apart. NOAA forecasters estimate a 35% chance of X-flares and a 75% chance of M-flares on June 1st.

Source: https://spaceweather.com/