Description
In collisionless plasma, several processes contribute to plasma heating and energy dissipation. One such example is wave-particle interactions between electromagnetic whistler waves and electrons. In the solar wind, the whistler-heat flux instability is known to regulate the electron heat flux by pitch-angle scattering of strahl electrons. Similar instabilities are believed to operate in various astrophysical plasma, but most such systems can only be studied remotely and through simulations. The Earth’s magnetosheath downstream of the bow shock is accessible to high-quality in situ spacecraft measurements, allowing the measurement of heat flux and detailed studies of wave-particle interactions. The heat flux properties and evolution across the magnetosheath have not yet been explored.
We present Magnetospheric Multiscale (MMS) observations from 18 hours of high-resolution burst-mode measurements. We quantify the electron heat flux in the magnetosheath and examine the role of whistler instabilities in regulating it. Our results show that the heat flux follows the magnetosheath magnetic field as it drapes around the magnetosphere. We find that the heat flux is constrained by whistler instability thresholds and is aligned with the propagation of low-frequency whistler waves. We also present a case study investigating direct evidence for the whistler-heat flux instability in the magnetosheath.