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Pick‐up ions and the 2–3 kHz radio emissions
Author(s) -
Mitchell J. J.,
Cairns Iver H.,
Heerikhuisen J.
Publication year - 2009
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 - 10.1029/2009gl037898
Subject(s) - heliosphere , physics , solar wind , energetic neutral atom , ion , plasma , atomic physics , computational physics , magnetic field , supersonic speed , nuclear physics , mechanics , quantum mechanics
The 2–3 kHz radio emissions observed by the Voyager spacecraft are thought to turn on where pick‐up ions drive lower‐hybrid waves. Previous work focused on pick‐up ions born via charge exchange with neutrals from the inner heliosheath. However, Boltzmann simulations show that inner heliosheath neutrals have significantly lower speeds after crossing the heliopause compared with fluid simulations. We calculate the pick‐up ion distributions resulting from charge exchange with various neutral species, finding that neutrals born in the supersonic solar wind give a ring‐beam distribution, but inner heliosheath neutrals do not. The emission theory survives with supersonic solar wind neutrals as the pick‐up ion source. This leads to increases in the ring‐beam and electron tail speeds, available lower‐hybrid wave energy, and radio flux. Larger ring speeds increase the necessary magnetic field to ≳0.2 nT, constraining the source location, and predicting magnetic field strengths agreeing with heliosphere and interstellar medium models.