VLF 1) emissions from the ionosphere.
25 sec on 1600 ASA @ 20 mm/2,8

 

 

  

The magnetic activities that follows an Aurora, may also generate audiable electrical signals. With a simple electronic equipment you can listen to them. These sounds lag the main phase of the Aurora by typically 6 - 12 hours, with a significant occurance at dawn.

More common is the whistlermode of the ionosphere. Lightning is the major contributor to this kind of sound.

The spectrograms below show the complex and endless variation, with or without magnetic unrest.

  A whistler's signature         The aftermath of Aurorae 

 

 A multireflexion whistler. Decreasing amplitude and increasing dispersion is in effect. Note the timescale. Some 30 seconds are seen.

 

 Dawn chorus. Also two hissbands are evident.
The night was magnetically active.
 

A cluster of risers. The local magntic condition was quiet.

 

Intense broandband hiss.
The aftermath of a major magnetic storm during the night.
 

 Some pure tones. Some magnetic activity.

Hooks are abound. Magnetic quiet condition.
 

 Whistler mania. The now obsolete Omega is visible.
No magnetic activity.

1) Very Low Frequency electromagnetic energy