Plasma rest frame frequencies and polarizations of the low‐frequency upstream waves: ISEE 1 and 2 Observations

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Abstract
Using magnetic field data from the dual ISEE 1 and 2 spacecraft we have determined the plasma rest frame frequencies and polarizations of the large amplitude low frequency (0.03 Hz) upstream waves. The monochromatic sinusoidal waves associated with ‘intermediate’ ion fluxes are magnetosonic waves with rest frame frequencies ∼0.1 ΩP and wavelengths ∼1 RE. The obliquely propagating ‘shocklet’ form of the waves is also predominantly in the magnetosonic mode, but occasionally also appears in the Alfven mode with similar rest frame frequency and wavelength. The generation of the magnetosonic mode has been explained by the well established cyclotron resonance mechanism driven by narrow reflected ion beams but the concurrent observation of Alfven mode waves appears to require wave generation by the more isotropic diffuse ion distributions as well.