William Liu - The Dynamic Magnetosphere

(1)

(2)

(3)

(4)

(5)

(6)

Earths magnetopause and boundary layers have been widely studied over the last few decades. They have been, and will continue to be, major research targets of many satellite missions such as ISEE, Geotail, Wind, Polar, Interball, Equator-S, Cluster, Double-Star, THEMIS, and in the near future MMS. A number of previous reviews and collections of articles have appeared on the topic, notably those by Song et al. (). For early works and detailed descriptions of the solar wind plasma entry mechanisms that will be addressed here, the reader is referred to these reviews. For the present review, we build on those earlier ones and focus on current efforts that address the role the magnetopause and its boundary layers play in magnetospheric dynamics.

At the interface between two plasma regions, a number of instabilities may mediate plasma transfer and mixing. Of importance for the Earths magnetopause are magnetic reconnection (e.g., tearing mode instability), the KelvinHelmholtz instability (triggered by a velocity shear), and diffusive processes (for example mediated by waveparticle interactions). For the magnetopause, the proof that plasma of solar wind origin does protrude through the boundary comes from frequent in situ observations of mixed magnetospheric and solar wind plasmas just inside and adjacent to the main current sheet: the magnetopause boundary layer. With the advent of multi-spacecraft missions such as Cluster and THEMIS, together with new methods and enhanced instrumental and computer simulation capabilities, many new insights have been gained regarding the aforementioned mechanisms and the role they play in controlling the entry of solar wind plasma into the magnetosphere.

In Section then highlights the importance of magnetic reconnection and the KH instability in the context of global solar windmagnetosphere coupling, as well as in terms of possible solar wind plasma pathways to the magnetotail.

Magnetic reconnection at the magnetopause is believed to play a major role in solar windmagnetosphere coupling. Accompanying the large-scale magnetic topology changes which occur as a result of magnetic reconnection, mass, energy and momentum of the solar wind are transferred to the magnetosphere. Magnetic reconnection is the primary driver mechanism during enhanced geomagnetic activity. In this section we first describe some basic features of magnetopause reconnection and then present recent results on the topic. We do not address the issue of the initiation process of magnetic reconnection.