Alfvenic‐coupling algorithm for global and dynamical magnetosphere‐ionosphere coupled system

Abstract

This study proposes a new formula that describes a dynamical magnetosphere‐ionosphere (MI) coupling system through the field‐aligned current (FAC) closure and electrostatic potential connectivity. In the past, MI coupling processes were described as either “inductive” or “static.” The inductive coupling scheme is based on the reflection of MHD waves at the ionosphere, whereas in the static coupling scheme the electrostatic potential is determined through the FAC closure. In contrast, in our new formulation these two schemes are combined by the “Alfvenic‐coupling” algorithm. The concept of the Alfvenic coupling is as follows. When a distribution of ionospheric current is changed from the background condition through the mapping of magnetospheric disturbances and/or by the change of ionospheric conductivity, an ionospheric reflection electric filed is instantaneously generated to satisfy the current continuity condition. The electrostatic potential of this reflection field also feeds back to the magnetosphere and excites shear Alfvenic disturbances in the magnetosphere. Therefore, the current continuity condition has to include the FAC of Alfvenic disturbances. In this sense, the reflection potential is not only a modification of the ionospheric potential but also a source of inductive Alfvenic disturbances. Quantitative estimation of feedback components to the magnetosphere reveals that our new formulation is more suitable to global MI simulations than the static MI coupling, which has been the only scheme used in the past.