From: John F Booth, Palmer Station Science Technician
To:   VLF Group:  Stanford University
CC:   Marian Moyher and Rob Edwards:  RPSC
      Bob Farrell:  Palmer Station

Hi all,

   As previously referenced a couple of times, there were
some interesting periods of "noise" in the VLF hut at the
end of last month.

   Around 0 - 1 UT on 30 July, the odd noises were little
chirps.  I sent a clip of similar events last year, but
these are better, and come with visuals, too!  All of the
files mentioned are (or will be) in the data/2000special
directory.

 n2120020.mp3 is a fairly typical sample, that happened to
fall within a synoptic window, so that I can send you a
spectrogram from the broadband digital system, too (sorry
about the odd file names, but the image is bn200212.jpg).
The audio extends for longer than the spectrogram, in
order to catch a couple of the chirping periods.

 n2120019.mp3 is an extended period of chirping that seems
to be rising in pitch as it proceeds.  Or maybe it's three
sets of chirps one over the other.  It didn't hit a synoptic
window, but I've made a spectrogram of the original audio
WAVE clip using a piece of shareware.  That file is (more
logically) n2120019.jpg.  Since the sampling was at the
"CD rate" of 44.1 kHz, the spectrogram tops out at 22kHz.

 n2120023.mp3  is the longest clip, and it's actually not
fully ftp'd as I write this, but I hope that it will get
through this (Friday) AM;  if not I will force it through
in the afternoon.  Again it fell outside of the synoptic
windows, but I've made two images: n2120023.jpg shows the
whole clip and z2120023.jpg is a zoomed piece, showing a
bunch of wild fine structure.  Even without the structure,
the extended series of chirp-groups is bizarre.

   You'll notice a volume change at this point;  the three
clips described above were sampled with the monitor output
presenting the line receiver's AUX output, with a 20 dB
gain, but the ones after this were from the MIX output,
with 33 dB gain.  Adjust your speakers accordingly. :-)

 n2120050.mp3 has a couple of "typical" sets of chirps, one
at about 4 seconds into the clip (before the cal tone) and
the other at about 15 seconds in, except that after the
latter set it settles down into an EXTENDED run of a
slightly wavy roughly 3kHz tone.  This did hit a synoptic,
so a broadband PC produced spectrogram can be seen as
bbn00212.jpg.

   The other interesting time was the next day, but in the
AM, circa 1030-12 UT.  Rather than describe it, I'll let
you hear and see for yourselves.  The period of interest
was much more homogeneous, so I just grabbed a couple of
clips that overlapped with synoptic samples.  The clips
are  n2131105.mp3 and  n2131120.mp3; the corresponding images
are bbn00213.jpg and bn200213.jpg.  In each case the clip
starts before the spectrogram; you can synchronize your
eyes and ears on the cal tones.

   OK, I will say a little.  I hear four things in these:
the "regular" sferics and whistlers, then an overlying
"layer" of chirping, and finally an underlying layer of,
well, it's hard to find the right word for it.  Muttering?
Whispering?  Burbling?  I can't see anything very special
on the spectrograms, though I will say that my eye is drawn
to the "splotch" right below the whistler at 10 seconds on
bbn00213.jpg.  But this doesn't seem likely to be relevant
to the more continuous noises.  Maybe they're just too
faint for the resolution of the spectrograms.

   The spectrograms of the chirping look not unlike the one
that I sent earlier this winter that Bill suggested was of
triggered emissions.  This stuff, too?  What causes some
whistlers to trigger emissions but most not to?  And what
about the "atypical" extended chirping periods (without
strong whistlers to be triggers) and the weird 3 kHz
holdover tone?

   And the alien whisperings?  Have I just been here too
long?? :-)

   Oh, one other thing.  You may have noticed, or if not
allow me to call your attention to, a "special" phase
plot from Day 213, I think it was.  That was one of those
inexplicable days when the phases seemed less noisy, and
I was actually able to see a few little events on one of
the channels.  Just FYI that there is SOME information
there....

Adios,
Johan.