Langmuir cavitons have been artificially produced in the earth's ionosphere,
but evidence of naturally-occurring cavitation has been elusive. By measuring
and modeling the spectra of electrostatic plasma modes, we show that natural
cavitating, or strong, Langmuir turbulence does occur in the ionosphere, via a
process in which a beam of auroral electrons drives Langmuir waves, which in
turn produce cascading Langmuir and ion-acoustic excitations and cavitating
Langmuir turbulence. The data presented here are the first direct evidence of
cavitating Langmuir turbulence occurring naturally in any space or
astrophysical plasma.Comment: 4 pages, 4 figures, published in PRL on 9 March 2012
http://link.aps.org/doi/10.1103/PhysRevLett.108.10500
