[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-12] Dawn-dusk asymmetry in the mesoscale field-aligned currents embedded in the diminished large-scale Region 1 current

*Yoshihiro Yokoyama¹, Satoshi Taguchi¹, Toshihiko Iyemori² (1.Department of Geopysics, Graduate School of Science, Kyoto University, 2.Kyoto University)

Keywords:field-aligned currents, northward IMF

Irregular magnetic perturbations embedded in the diminished large-scale Region 1 current are observed in almost all MLT except for the near noon region during prolonged northward IMF conditions. Our recent statistical study for the dusk side sector has revealed that the mesoscale field-aligned currents that produce these irregular magnetic perturbations tend to occur under the northward IMF conditions and are possibly generated in the low-latitude boundary layer. Our study has also shown that the current density of the mesoscale field-aligned currents tends to increase as the solar wind proton density increases. To clarify whether or not there exist asymmetries in the mesoscale field-aligned currents between the dawn and dusk sector, by utilizing magnetic data obtained by Swarm satellites during the period from May 2014 to May 2017, we investigated the dependence of the dawn side field-aligned currents on the solar zenith angle, the IMF, and solar wind plasma parameters, and compared the results with those from the dusk side sector. We found that the occurrence ratio of the mesoscale field-aligned current in the dawn sector also shows a strong dependence on the northward IMF condition. Besides, we found that there are weak dawn-dusk asymmetries in the occurrence ratio against the Y component of IMF, and in the current density. From our proposed mechanism of the generation for the mesoscale field-aligned currents, which is associated with the cold dense ion regions in the low-latitude boundary layer, we interpret those dawn-dusk asymmetries.