[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-11] Energy input to the ionosphere and ELF waves during geomagnetic storm events in the cusp

*Naritoshi Kitamura¹, Lynn M. Kistler², Masafumi Hirahara¹, Kai Zhao³, Eric J. Lund^2,4 (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, 3.School of Mathematics and Statistics, Nanjing University of Information Science and Technology, 4.College Brook Scientific)

Keywords:Ion outflow, Cusp, FAST satellite

The ionosphere is an important source of magnetospheric plasma, especially for heavy ions with low charge states. The region near the cusp is one of the most important regions for ion outflows. Although ion acceleration perpendicular to the magnetic field by broadband ELF waves is thought to be important for driving ion outflows near the cusp, even the intensity of the waves is not well understood. We investigate the energy input to the ionosphere and the ELF waves during geomagnetic storms as likely extreme cases using data obtained by the Fast Auroral SnapshoT (FAST) satellite. The precipitating electron number density and Alfven Poynting flux in and near the cusp (1000-1400 MLT) exhibit a relatively good correlation with a (broadband) ELF wave intensity at ~10 Hz, which is close to the upper limit of the frequency available in the slow survey mode and is close to the local O⁺ cyclotron frequency at ~4000 km altitude. During geomagnetic storms, the broadband ELF wave can become much more intense than the intensity often assumed by simulations of ion outflows [e.g., Barakat and Schunk, JASTP, 2001; Horwitz and Zeng, JGR, 2009; Glocer and Daldorff, JGR, 2022]. Ion outflow events with enhanced fluxes are associated not only with large energy inputs (electron precipitation and Poynting flux) but also with the intense broadband ELF waves around the ion cyclotron frequencies. Although such intense ELF waves are latitudinally localized along the cusp under southward interplanetary magnetic field conditions, they will be an important contributor to ion acceleration during geomagnetic storms due to their large intensity.