Structure and Dynamics of the Magnetopause and Its Boundary Layers

Abstract

The magnetopause is the key region in space for the transfer of solar wind mass, momentum, and energy into the magnetosphere. During the last decade, our understanding of the structure and dynamics of Earth's magnetopause and its boundary layers has advanced considerably, thanks largely to the advent of multi-spacecraft missions such as Cluster and THEMIS. Moreover, various types of physics-based techniques have been developed for visualizing two-or threedimensional plasma and field structures from data taken by one or more spacecraft, providing a new approach to the analysis of the spatiotemporal properties of magnetopause processes, such as magnetic reconnection and the Kelvin-Helmholtz instability (KHI). Information on the size, shape, orientation, and evolution of magnetic flux ropes or flow vortices generated by those processes can be extracted from in situ measurements. Observations show that magnetopause reconnection can be globally continuous for both southward and northward interplanetary magnetic field (IMF) conditions, but even under such circumstances, more than one X-line may exist within a certain (low-latitude or high-latitude) portion on the magnetopause and some X-lines may retreat anti-sunward. The potential global effects of such behavior are discussed. An overview is also given of the identification, excitation, evolution, and possible consequences of the magnetopause KHI: there is evidence for nonlinear KHI growth and associated vortex-induced reconnection under northward IMF. Observation-based estimates indicate that reconnection tailward of both polar cusps can be the dominant mechanism for solar wind plasma entry into the dayside magnetosphere under northward IMF. However, the mechanism by which the transferred plasma is transported into the central portion of the magnetotail, and the role of magnetopause processes in this transport, remain unclear. Future prospects of magnetopause and other relevant studies are also discussed.

Evolution of the magnetic field structure outside the magnetopause under radial IMF conditions

“…[] argued that single lobe reconnection forms the outer LLBL, whereas the inner LLBL is on closed field lines. It means that the MSBL of Hasegawa [] and the outer LLBL of Le et al . [] are on the same field lines, but the name MSBL emphasizes an extension of the field lines to the magnetosheath, whereas the LLBL suggests that it is a part of the magnetosphere.…”

MAVEN observations of partially developed Kelvin‐Helmholtz vortices at Mars

“…An interesting feature to note here is the large pressure perturbations associated with these boundary oscillations (see Figure e). Such large pressure perturbations are observed for fully developed KH vortices at Earth [ Hasegawa , ]. However, since we determined that the KH vortices are not fully developed, what could be causing such large pressure perturbations?…”

On the origins of magnetic flux ropes in near‐Mars magnetotail current sheets

“…Alternatively, we can explore the second possibility that does not necessitate magnetotail reconnection: transport of flux ropes that are originally generated in the dayside ionosphere through plasma instabilities such as helical kink, Kelvin‐Helmholtz instabilities [e.g., Elphic and Russell , ; Wolff et al , ; Ruhunusiri et al , ], and magnetic reconnection in consequence of interactions between the IMF and crustal fields [e.g., Hara et al , , ], or dayside magnetic reconnection analogous to the terrestrial flux transfer events [see, e.g., Hasegawa , , and references therein]. As illustrated in Figure b, these helical draped magnetic field lines can be subsequently transported into the nightside magnetotail forming the current sheet, allowing spacecraft to detect them as flux ropes embedded in the magnetotail current sheets.…”