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Abstract

Ion outflow from high-latitude region of Earth's ionosphere is an important source of the ions in the magnetosphere. As a part of ionosphere-magnetosphere coupling, it is also an important driver of dynamics in the magnetosphere. The dawn-dusk asymmetries in the ion outflow are sometimes non-negligible for the outflow processes and plasma circulation in geospace. The causes of the asymmetries are diverse in terms of the morphologies, efficiencies, and responses to the solar-wind conditions. In this review, we focus on the mechanisms of dawn-dusk asymmetries in energization of ion outflow and in the ion transportation in the magnetotail. Asymmetric energization processes are: (1) asymmetry in auroral precipitation associated with electron heating, ion beams and conics; (2) asymmetry in Poynting flux associated with ion heating; (3) asymmetry in cusp spatial distributions that causes various heating on the dayside; (4) high-altitude ionosphere-magnetosphere-coupled convection with IMF controlled dawn-dusk asymmetry which is essential to centrifugal acceleration for transportation of polar cap ion outflow.