Observations in 2017
Joachim Köppen Kiel 2018
  
   Click on blue-rimmed images to enlarge. On Oct. 15th, 2017 at the beach of the Baltic Sea, all types of emissions could 
  be heard: When I started listening at about CEST 15:00, I heard apart from the ever-present
  spherics and the strong clicks (every 1.2 seconds) from an electric fence which was guarding 
  a flock of sheep ... something unusual: There were musical tones rising in frequency, resembling 
  the chirping of birds. After a while it became obvious that these tones were not break-through 
  music from the radio program of the strong  
  AM transmitter at Kalundborg...
   Here is one riser in more detail. Fortunately it occurred well in between two loud clicks 
  from the sheep fence:
   Later, after CEST 16:55, with the approaching dawn, tweeks appeared in great
  numbers and strength. By this time, I was well away from the sheep fence.  
   Also, several multi-component whistlers could be heard:
   
 
 
 
   
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   last update:   Apr 2018  J.Köppen
  These are risers, part of chorus emission:
  
   
      
  
  listen to the sound file
  
   
      
  
  listen to the sound file
  
   
      
  
  listen to the sound file
  
   
      
  
  listen to the sound file
  
  
  Since the frequency of a whistler decreases roughly like the square root of the time after 
  its start, a plot with a logarithmic frequency scale should give nearly straight lines. 
  One sees that this is not quite the case: 
  
   
     