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Abstract

The terrestrial magnetopause is a thin current sheet forming the boundary between the solar wind and the Earth's magnetosphere. It is thus a key region for the transfer of energy and momentum from the solar wind to the magnetosphere. In this chapter, we show observations suggesting significant and persistent differences between the dusk and dawn flank in many macroscopic parameters and properties of the magnetopause. Some of the asymmetries can be explained by differences in boundary conditions, in particular, properties of the adjacent magnetosheath, which, in turn, is largely dictated by interaction between the bow shock and the interplanetary magnetic field. Asymmetries in the occurrence probability of Kelvin-Helmholtz waves, which seem to favor the dusk magnetopause flank, are also probably related to magnetosheath properties. There are also indications that an asymmetric ring current inside the magnetosphere can contribute to a corresponding magnetopause asymmetry, since an enhanced ring current will cause a larger magnetic shear across the magnetopause.