[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-13] On the relationship between energy input to the ionosphere and the ion outflow flux under different solar zenith angles

*Naritoshi Kitamura¹, Kanako Seki¹, Kunihiro Keika¹, Yukitoshi Nishimura², Tomoaki Hori³, Masafumi Hirahara³, Eric J. Lund^4,5, Lynn M. Kistler⁴, Robert J. Strangeway⁶ (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 2.Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, 3.Institute for Space-Earth Environmental Research, Nagoya University, 4.Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, 5.College Brook Scientific, 6.Department of Earth, Planetary, and Space Science, University of California, Los Angeles)

Keywords:Ion outflow, FAST satellite, Auroral zone, Cusp

The ionosphere is an important source for magnetospheric plasma, particularly for heavy ions with low charge states. We investigate the effect of solar illumination on the number flux of ion outflow using data obtained by the Fast Auroral SnapshoT (FAST) satellite at 3000–4150 km altitude from 7 January 1998 to 5 February 1999. We derive empirical formulas between energy inputs and outflowing ion number fluxes for various solar zenith angle ranges. It is found that the outflowing ion number flux under sunlit conditions increases more steeply with increasing electron density in the loss cone or with increasing precipitating electron density (above 50 eV), compared to the ion flux under dark conditions. Under ionospheric dark conditions, weak electron precipitation can drive ion outflow with small averaged fluxes (about 10⁷ cm²/s). The slopes of relations between the Poynting fluxes and outflowing ion number fluxes show no clear dependence on the solar zenith angle. Intense ion outflow events (larger than 10⁸ cm²/s) occur mostly under sunlit conditions (solar zenith angle < 90°). Thus, it is presumably difficult to drive intense ion outflows under dark conditions, because of a lack of the solar illumination (low ionospheric density and/or small scale height owing to low plasma temperature).