At higher altitudes, there isn’t enough air for ionized molecules to combine and become neutral again, so the region stays ionized. That’s what the ionosphere is.

The remarkable thing is that it took an hour for it to come back from this disturbance. It’s a very unusual event and was three orders of magnitude more intense than the [1998] one, which...

Our response continued because the Earth of course didn’t saturate. The Earth is much too large a detector to saturate.

[Guglielmo] Marconi discovered global communication because of reflections from the ionosphere. Back at the turn of the century, he sent signals from England to the United States by reflecting them from the ionosphere.

We observed the ionosphere respond to that. The ionosphere was in fact pulsating at night.

This region has been called the ‘ignore-o-sphere’ because it isn’t an easy region to measure. The VLF technique that we have developed is particularly suitable for looking at this altitude range, which is not otherwise...