[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-05] Evolution of electrostatic potential in magnetosphere-ionosphere system as simulated by global MHD model with Alfvénic-coupling

*Aoi Nakamizo¹, Akimasa Yoshikawa², Hiroyuki Nakata³, Keiichiro Fukazawa⁴, Takashi Tanaka² (1.Radio Research Institute, National Institute of Information and Communications Technology, 2.Faculty of Science, Kyushu University, 3.Graduate School of Engineering, Chiba University, 4.Academic Center for Computing and Media Studies, Kyoto University)

Keywords:M-I coupling, Alfvenic-coupling algorithm, Global magnetosphere MHD simulation, Ionospheric conductance

By using the Polarization Field Separation method [Nakamizo and Yoshikawa, 2019] and a global MHD model [Tanaka, 2015], we have shown that the ionosphere plays an active role in the configuration and dynamics of the global magnetosphere due to its non-uniform conductance distribution. The feedback process from the ionosphere to the magnetosphere in the current global MHD simulations can be described as follows; (1) The ionospheric conductance non-uniformity generates polarization fields, thereby deforming the ionospheric electric potential pattern. (2) The information of deformation is reflected in the magnetospheric bulk velocity updated by the potential mapped back to the magnetospheric inner boundary (V_perp=-(ExB)/B²). (3) The updated velocity disturbances propagate the magnetosphere, modifying the force and energy balance of MHD field. (4) The FAC distribution at the next time step is calculated in the magnetosphere updated in this way and is inputted again to the ionosphere, generating the ionospheric potential of the next time step. (5) Thus, the effect of ionospheric polarization fields is accumulatively included in the development of the magnetosphere–ionosphere system.

In order to investigate precisely the role of ionosphere, we implement Alfvénic-coupling algorithm proposed by Yoshikawa et al. [2010] in the MHD code. In the Alfvénic-coupling algorithm, both FACs and potential are mapped between the magnetosphere and ionosphere in terms of the incident and reflection process of shear Alfvén waves, therefore the continuities of physical quantities and the conservations of momentum and energy are ensured. As an implementation test, we show how the reflected FACs, reflected potential, and total (M-I coupled) potential change depending on the ratio of Pedersen conductance and Alfvén conductance. We also compare the total FACs, total potential, and velocity perturbations around the inner boundary obtained by the normal coupling and Alfvénic-coupling.