Solar X-rays:

Geomagnetic Field:

ELF is from 3 HZ to 30 Hz.

VLF is from 3 Khz to 30 Khz

ULF is from 300 Hz to 3 Khz

Here is a link to a complete list of frequency ranges and a complete explanation of various bands.

The following links are from the web site, “Radio Waves below 22 KHZ,” by  IK1QFK, Renato Romero, and they deal with “Unexplained ULF-ELF Signals.”  There are 3 parts to this series, and it shows waves that were recorded from a ULF - ELF receiver.