Below shows lightning-generated sferics (vertical lines) from our lightning sensors and narrowband signals (horizontal lines) from VLF transmitters. Each spectrogram spans a few seconds in time (horizontal axis) and between 32 and 48 kHz in frequency (vertical axis). All start at precisely the same time at exactly on the minute min past each hour and include data for the next few seconds as indicated. Click on any thumbnail below to expand it to full size (or click on its caption to open it on a new page).