Excitation of plasma waves by unstable photoelectron and thermal electron populations on closed magnetic field lines in the Martian ionosphere

Abstract

Abstract. It is argued that anisotropic electron pitch angle distributions in the closed magnetic field regions of the Martian ionosphere gives rise to excitation of plasma instabilities. We discuss two types of instabilities that are excited by two different populations of electrons. First, the generation of Langmuir waves by photoelectrons with energies of the order of 10 eV is investigated. It is predicted that the measured anisotropy of their pitch angle distribution at the heights z≈400 km causes excitation of waves with frequencies f ∼30 kHz and wavelengths λ∼30 m. Near the terminators the instability of the electrostatic waves with frequencies of the order of or less than the electron gyrofrequency exited by thermal electrons is predicted. The typical frequencies of these waves depend on the local magnitude of the magnetic field and can achieve values f ∼3−5 kHz above strong crustal magnetic fields.

Perspective on Energetic and Thermal Atmospheric Photoelectrons

“…Thermalized photoelectrons permeate planetary ionospheres and magnetospheres creating polarization electric fields (e.g., Axford, 1968) and plasma waves as they interact with ions to maintain charge neutrality (e.g., Borisov and Nielsen, 2005). They carry field aligned currents (e.g., Carlson et al, 1998b) and transfer energy via a heat flux between the ionosphere and magnetosphere (e.g., Kozyra et al, 1987;Khazanov et al, 2020).…”