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

Near-f_ce 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_ce harmonic waves are strongly connected to the magnetic field direction. We express the magnetic field direction in terms of spherical angles, where θ_B is the elevation angle and φ_B is the azimuthal angle. Then, we show that near-f_ce harmonics emissions occur when the magnetic field points in a narrow angular range, bounded by 80° ≤ θ_B ≤ 100° and 10° ≤ φ_B ≤ 30°, in most of the cases. We also show that the influence of magnetic field direction on near-f_ce 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_ce 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.