Magnetosonic Waves Driven by Maxwellian Ring Protons in the Martian Upper Ionosphere

Abstract

Magnetosonic (MS) waves can be generated by hot Maxwellian ring protons locally within the Martian upper ionosphere, characterized by a weak ambient magnetic field and the presence of cold plasma abundant in heavier ions. A comprehensive study on the resonant instabilities of MS waves making use of the derived growth rates show that ring proton population with energies around 100 eV is optimal for wave generation. Highly oblique propagation leads to sharp harmonic structures at frequencies closer to local proton gyrofrequency. An increase in ring energy, ${\omega }_{pe}/{\Omega }_{ce}$ ratio, and heavier ion concentration decreases the wave growth rates. When the background ions have very low temperatures, $O_2^{+}$ ions lower the growth rate more as compared to $O^{+}$ ions. Additionally, the increase in temperatures of cold electrons and ions have opposite effects, with the former increasing the growth rate and the latter decreasing it.