TERRAPUB Monographs on Environment, Earth and Planets


Monogr. Environ. Earth Planets, Vol. 1 (No. 2), pp. 71-119, 2012 doi:10.5047/meep.2012.00102.0071 ISSN: 2186-4853

Structure and Dynamics of the Magnetopause and Its Boundary Layers

Hiroshi Hasegawa

Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan

(Received July 1, 2011; Revised April 6, 2012; Accepted April 16, 2012; Online published August 7, 2012)

Citation: Hasegawa, H. (2012), Structure and dynamics of the magnetopause and its boundary layers, Monogr. Environ. Earth Planets, 1, 71-119, doi:10.5047/meep.2012.00102.0071.

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 three-dimensional 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.

Keywords: Magnetopause, Low-latitude boundary layer, Magnetic reconnection, Kelvin-Helmholtz instability, Solar wind-magnetosphere interaction, Plasma transport, Collisionless plasma, Multi-spacecraft observations.

Corresponding author e-mail: hase@stp.isas.jaxa.jp


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