He doesn't know, but sent the info to the ARRL dot org web site. I read the Quanta web site & it has fairly good reporting & answers.

It could be any number of things, all people know is there was some kind of long pop or ping maybe a slap or even a bang but where did it come from, maybe inside the Earth some kind of iron burp a rumble in the stomach, from deep within the Earth so to speak, maybe it was some burst of energy and ions to from the Sun move back from Jupiter passes our Moon as the long ago forgotten dust from some comet arrived in our upper atmosphere, maybe it was something to do with our Sun and Solar Flares, maybe its some far off deadly Cosmic gamma event in our universe or maybe its the fact our Pole has decided to move itself these past months, we are only here in the blink of an eye and these magnetic slaps happen often enough in our Billions upon Billions of years as a Planet. Magnetometer, Satellite cams, Geophysicists all these people can measure things, electromagnetic levels, but if an event happens, it needs to be recorded to be studied you need to be in the right place at the right time otherwise the data is lost. My guess is the Europeans have something, they launched a lot of Earth observation sats, they study the Earth’s Magnetosphere, also did something with the Chinese called the 'Cluster' mission and they also have 'Swarm', some worked in Italy others Germany, France or University of Denmark, there is NASA’s Magsat mission and Polar Orbiting Geophysical Observatory, the German CHAMP satellite, and the Danish Oersted satellite, also a public open website covers some of this stuff weekly 'space weather' dot com might be the internet site, the ESA however is sometimes a little closed and not as open as NASA with their data.