Electron velocity-space scattering from whistler waves in the Earth’s magnetosheath

Whistler waves are found in various space plasma environments, such as the Earth’s magnetosheath, where they affect particle dynamics and energy transfer. Through wave-particle interactions, they contribute to changes in both the energy and pitch angle of electrons. However, the significance of whistler waves in different plasma regions is not fully known.

In this work, we use MMS measurements to calculate the occurrence and properties of whistler waves in the Earth’s magnetosheath. Based on selected MMS orbits, we compare the plasma conditions offered by the more stationary quasi-perpendicular (Q_⊥) to the more fluctuating quasi-parallel (Q_॥) magnetosheath. We show that the whistler waves occur in local magnetic dips and density peaks and are not necessarily correlated with electron temperature anisotropy. Also, there is an elevated occurrence downstream of Q_⊥ shocks, compared to the Q_॥ configuration. Further, by calculating pitch-angle diffusion coefficients, we find that whistler waves can significantly reshape the electron velocity distribution during the time a plasma parcel spends in the magnetosheath, which has important implications for the plasma dynamics of the magnetosheath region.