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Plasma wave generation near the inner heliospheric shock
Author(s) -
Macek W. M.,
Cairns I. H.,
Kurth W. S.,
Gurnett D. A.
Publication year - 1991
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/90gl02594
Subject(s) - physics , heliosphere , bow shock (aerodynamics) , solar wind , bow wave , shock wave , heliospheric current sheet , plasma , computational physics , geophysics , astronomy , interplanetary magnetic field , mechanics , quantum mechanics
There is mounting evidence that the Voyager 1 and 2 and Pioneer 11 spacecraft may approach the inner (termination) heliospheric shock near the end of this century. It is argued here, by analogy with planetary bow shocks, that energetic electrons backstreaming from the heliospheric shock along the magnetic field should be unstable to the generation of Langmuir waves by the electron beam instability. Analytic expressions for the cutoff velocity, corresponding to the beam speed of the electrons backstreaming from the shock, are derived for a standard solar wind model. At the front side of the heliosphere the maximum beam velocity is expected to be at the meridian passing through the nose of the shock, which is assumed aligned with the Very Local Inter‐Stellar Medium (VLISM) flow. This foreshock region and the associated Langmuir waves are relevant to both the expected in situ observations of the heliospheric boundaries, and to the low‐frequency (2–3 kHz) radio emissions observed by the Voyager spacecraft in the outer heliosphere. Provided that these radio emissions are generated by Langmuir waves, the minimum Langmuir wave electric fields at the remote source are estimated to be ≳ 3–30 μV/m.