The emission of near-fce harmonic waves at small radial distances from the Sun

Abstract

<p>Near-f<sub>ce</sub> harmonic waves are prevalent in the high-frequency electric field spectrum during Parker Solar Probe's (PSP) close encounters with the Sun. These waves are electrostatic and tend to occur in regions of a relatively stable magnetic field with low broadband magnetic fluctuation levels. We show that the emissions of near-f<sub>ce</sub> harmonic waves are strongly connected to the magnetic field direction. We express the magnetic field direction in terms of spherical angles, where θ<sub>B</sub> is the elevation angle and φ<sub>B</sub> is the azimuthal angle. Then, we show that near-f<sub>ce</sub> harmonics emissions occur when the magnetic field points in a narrow angular range, bounded by 80° ≤ θ<sub>B</sub> ≤ 100° and 10° ≤ φ<sub>B</sub> ≤ 30°, in most of the cases. We also show that the influence of magnetic field direction on near-f<sub>ce</sub> harmonic waves goes down to the shortest time scales the FIELDS instrument can access. These results suggest that cross-scale interaction might play an essential role in the dynamics of the near-f<sub>ce</sub> harmonics measured by PSP at small radial distances from the Sun. It may also provide important clues about the origin of these waves and their role at the early stages of solar wind evolution.</p>