[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-04] Alfvénic structure at 500 km altitude in the cusp and its relation to mesoscale electron precipitation regions

*Satoshi Taguchi¹, Haruto Koike¹, Keisuke Hosokawa² (1.Department of Geophysics, Graduate School of Science, Kyoto University, 2.Graduate School of Informatics and Engineering, University of Electro-Communications)

Keywords:Aurora, Cusp, Alfvén wave, Field-aligned current

In order to understand how the Alfvénic structures identified at an altitude of about 500 km in the cusp are related to the variability of the electron precipitation seen as the motion of the red aurora, we examined two cases in which two Swarm satellites passed through the cusp with a time lag of about 1 minute and the red aurora was simultaneously observed on the ground. Analysis of 50 Hz magnetic field data acquired by Swarm A and Swarm B has shown that there are a few areas where the power of the magnetic fluctuations with frequencies between 0.5 Hz and 10 Hz is strongly enhanced. The analysis has also shown that these locations are at the poleward or equatorward boundaries of the upward field-aligned current with a larger spatial scale. Comparison with red aurora data has shown that these locations are also at the poleward or equatorward boundaries of the mesoscale red aurora. In addition, analysis of 16 Hz electric field data has shown that the Alfvénic structures tend to occur in the region where the background electric field is small compared to the magnitude of the maximum electric field observed in the cusp. Based on these observations, we discuss the extent to which Alfvén waves trapped in the ionospheric Alfvén resonator are related to the electron precipitation that causes the red aurora in the cusp.