Localized Heating of the Martian Topside Ionosphere Through the Combined Effects of Magnetic Pumping by Large‐Scale Magnetosonic Waves and Pitch Angle Diffusion by Whistler Waves

Abstract

We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of periodic ( ∼25 s) large‐scale (hundreds of km) magnetosonic waves propagating into the Martian dayside upper ionosphere. These waves adiabatically modulate the superthermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe/ fce provides conditions favorable for the local enhancement of efficient wave‐particle interactions, so that the induced whistlers act back on the superthermal electron population to isotropize the plasma through pitch angle scattering. These wave‐particle interactions break the adiabaticity of the large‐scale magnetosonic wave compressions, leading to local heating of the superthermal electrons during compressive wave “troughs.” Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular‐to‐parallel superthermal electron temperatures and compressive wave fronts. This heating mechanism may be important at other unmagnetized bodies.

Rapid Landau Heating of Martian Topside Ionospheric Electrons by Large‐Amplitude Magnetosonic Waves

“…In spite of the limitation to parametric and idealized calculations, our study has provided a new candidate mechanism, Landau heating of electrons by magnetosonic waves, for the Martian ionospheric erosion. Future theoretical, observational, and modeling works are required to quantitatively evaluate the contributions of these physical mechanisms proposed here and previously (e.g., Collinson et al, 2018;Fowler et al, 2020) to the evolution of the Martian ionosphere.…”

“…On the contrary, Collinson et al (2018) hypothesized the energy transfer from the magnetosonic waves to the ionospheric plasma through some adiabatic compression processes rather than the wave-particle resonances. More recently, Fowler et al (2020) proposed that a combination of the adiabatic magnetic pumping by the large-amplitude magnetosonic waves and the pitch angle scattering by the induced whistler waves could heat the ionospheric suprathermal electrons.…”

Empirically Determined Auroral Electron Events at Mars—MAVEN Observations

“…Electron acceleration events at Mars have been identified with measurements from MGS (e.g., Brain et al, 2006;Halekas et al, 2008), MEx (e.g., Leblanc et al, 2008), andMAVEN (e.g., Akbari et al, 2019;. The acceleration mechanisms include, but are not limited to, narrow electrostatic potential layers within double-layers (associated with inverted-V electron events) (e.g., Brain et al, 2006;, acceleration associated with current sheet crossings (e.g., Halekas et al, 2008;Harada et al, 2020), and wave-particle interaction (e.g., Fowler et al, 2020Fowler et al, , 2021. Meanwhile, upstream solar wind electron fluxes can be significantly increased during solar transient events such as interplanetary coronal mass ejections and stream interaction regions (e.g., Xu, Curry, et al, 2020).…”

Modeling Wave‐Particle Interactions With Photoelectrons on the Dayside Crustal Fields of Mars

“…Above 250 km, the log of the densities are linearly extrapolated. The wave parameters used are representative of the observations by Harada et al (2016) and Fowler et al (2020). The wave power is assumed to be 10 −4 nT 2 /Hz.…”