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Detection of Hertz Frequency Multiharmonic Field Line Resonances at Low‐L ( L = 1.1–1.5) During Van Allen Probe Perigee Passes
Author(s) -
Lena F. R.,
Ozeke L. G.,
Wygant J. R.,
Tian S.,
Breneman A. W.,
Mann I. R.
Publication year - 2021
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 - 10.1029/2020gl090632
Subject(s) - physics , field line , electric field , harmonics , ionosphere , field (mathematics) , computational physics , line (geometry) , van allen probes , plasma , atomic physics , geophysics , magnetosphere , van allen radiation belt , quantum mechanics , geometry , mathematics , voltage , pure mathematics
We present new and previously unreported in situ observations of Hertz frequency multiharmonic mode field line resonances detected by the Electric Field and Waves instrument on‐board the NASA Van Allen probes during low‐L perigee passes. Spectral analysis of the spin‐plane electric field data reveals the waves in numerous perigee passes, in sequential passes of probes A and B, and with harmonic frequency structures from ∼0.5 to 3.5 Hz which vary with L‐shell, altitude, and from day‐to‐day. Comparing the observations to wave models using plasma mass density values along the field line given by empirical power laws and from the International Reference Ionosphere model, we conclude that the waves are standing Alfvén field line resonances and that only odd‐mode harmonics are excited. The model eigenfrequencies are strongly controlled by the density close to the apex of the field line, suggesting a new diagnostic for equatorial ionospheric density dynamics.