This
sound was present when PMEL began recording SOSUS
in August, 1991. It consists of a long train of narrow-band upsweeping
sounds of several seconds duration each. The source level is high enough
to be recorded throughout the Pacific. It appears to be seasonal, generally
reaching peaks in spring and fall, but it is unclear whether this is due
to changes in the source or seasonal changes in the propagation environment.
The source can be roughly located at 54o S, 140oW,
near the location of inferred volcanic seismicity, but the origin of the
sound is unresolved. The overall source level has been declining since
1991 but the sounds can still be detected on NOAA's equatorial autonomous
hydrophone arrays.
Click
on spectrogram for full-sized
image.
451K
wav file(The
recorded signal has been sped up 20 times)
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