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Buoyancy Waves in Earth's Nightside Magnetosphere: Normal‐Mode Oscillations of Thin Filaments
Author(s) -
Toffoletto F. R.,
Wolf R. A.,
Schutza A. M.
Publication year - 2020
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027516
Subject(s) - magnetosphere , physics , buoyancy , eigenfunction , normal mode , classical mechanics , wavelength , field line , plane (geometry) , plasma sheet , field (mathematics) , magnetic field , mechanics , computational physics , geometry , optics , eigenvalues and eigenvectors , quantum mechanics , mathematics , pure mathematics , vibration
We derive a coupled pair of differential equations that describe linear oscillations of a thin magnetic filament that slides without friction through a stationary medium that is in equilibrium. Background field lines are assumed to be in the xz plane, and filament motion is confined to that plane. Sample eigenfunctions and eigenfrequencies are computed for a numerical equilibrium that approximately represents the average magnetosphere but departs from exact equilibrium due to finite grid spacing and other numerical inaccuracy. The most important result of the calculation is the value of the eigenfrequency of the lowest even mode for filaments that cross the equatorial plane at y = 0 and −18 < x < −2 R E . The characteristics of the lowest even mode depend on geocentric distances of the field line. For field lines that extend out in the plasma sheet, that mode is characterized as a buoyancy wave but, for the inner magnetosphere, it is best characterized as a long‐wavelength slow mode.