Classifying the magnetosheath using local measurements from MMS

The Earth’s magnetosheath is a dynamic region and its properties strongly depend on the angle between the bow shock normal and the solar wind magnetic field (θ_bn). If the shock is quasi-parallel (θ_bn < 45°), the magnetosheath is magnetically connected to the foreshock, causing strong fluctuations and structures propagating from upstream to downstream. A quasi-perpendicular shock (θ_bn > 45°) produces a less structured and more stationary magnetosheath characterized by compression and high ion temperature anisotropy. These distinct configurations make it possible to study how different plasma environments affect various processes such as turbulence, heating, and wave-particle interactions. Therefore, such studies require an accurate classification of the magnetosheath. This is not easily achieved, especially close to the magnetopause where the shock crossing for the plasma of interest cannot be observed.

Previously, Karlsson et al. (2021) used data from the Cluster mission to propose a promising classification method using local measurements of the magnetic field standard deviation, high-energy ion flux, and ion temperature anisotropy. In this work, we are building on this study and extending it to the Magnetospheric Multiscale (MMS) mission, having a different orbit than Cluster. We compare this local classification to θ_bn estimated from upstream conditions and well-known bow shock models, and discuss the advantages and disadvantages of the different methods.

 

Reference: Karlsson, T., Raptis, S., Trollvik, H., & Nilsson, H. (2021). Classifying the magnetosheath behind the quasi-parallel and quasi-perpendicular bow shock by local measurements. Journal of Geophysical Research: Space Physics, 126, e2021JA029269.