Characteristics of Plasma Cavities That Appeared in the Intensity Dropout Event of Solar Energetic Particles

• Published in: The Astrophysical journal 2019-01, Vol.871 (1), p.104
• Main Author: Tan, Lun C.
• Format: Article
• Language: English
• Subjects: Alfven waves; Angles (geometry); Anisotropy; Astrophysics; Energetic particles; Holes; Magnetic fields; Magnetohydrodynamics; Solar cycle; Solar energetic particles; Solar wind; Solar wind velocity; Sun: heliosphere; Sun: magnetic fields; Sun: particle emission; Turbulence; Wavelengths; Waves; Whistler waves; Wind speed; Wind velocities
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aaf880

In order to explore the origin of the particle "dropout" phenomenon in the "gradual" solar energetic particle (SEP) event, we have selected 13 dropout intervals from 10 gradual SEP events during solar cycle 23. Our selection criterion is that within the dropout interval the average slab turbulence fraction is >0.8 in the ion dissipation range. In the plasma "cavity" that appeared in the dropout interval we have observed the angles of the wavenumber vector and the solar wind velocity vector relative to the mean magnetic field direction to be ∼0° and ∼90°, respectively. The distinctive feature of the cavity geometry could inhibit the occurrence of kinetic Alfvén waves (KAWs), leaving the dominance of magnetosonic-whistler waves in its plasma environment. Therefore, by examining the difference of turbulence characteristics between the dropout interval and the ambient solar wind, we are able to differentiate between the effects of KAWs and quasi-parallel whistler waves. Observations of the plasma β dependence of magnetic power density spectra in the ion dissipation range indicate that in the cavity of low plasma β (≤1) and low magnetic variance anisotropy (∼3) the turbulence cascade of the magnetosonic-whistler wave branch has reached a sufficiently developed stage.