[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-03] 磁気嵐時のカスプからのイオン流出の季節、太陽活動依存性のモデリング

*北村 成寿¹、Glocer Alex² (1.名古屋大学 宇宙地球環境研究所、2.NASA ゴダード宇宙飛行センター)

キーワード：イオン流出、イオン加速、カスプ

In this presentation, we show the results of simulations of ion outflows associated with soft electron precipitation, frictional heating, and acceleration due to broadband ELF (BBELF) waves in an idealized cusp region during geomagnetic storms under various seasons and solar activity levels. The cusp region has been regarded as a major source of magnetospheric O⁺ (and heavy ions), which increases greatly during geomagnetic storms. Under southward IMF conditions, the cusp becomes very thin in the latitudinal direction. Since poleward convection is expected in the cusp under southward IMF conditions due to the dayside reconnection on magnetic field lines at the equatorward edge of the cusp, flux tubes cannot stay a long time in the cusp, and the duration of ion acceleration in the cusp seen from a convecting flux tube is expected to be limited. For such a short duration of ion acceleration, we expect that the initial density profile will not change significantly during the acceleration, and thus the initial density profile is expected to have a large effect on the ion outflow rate. Here we show the results of simulations of ion outflows with 2-min acceleration under various seasons and solar activity levels with the kinetic polar wind outflow model (kinetic-PWOM) that can consider effects of soft electron precipitation, frictional ion heating, and ion acceleration due to broadband ELF (BBELF) waves. Under the assumption of the latitudinal width of the cusp as 1 degree and the poleward convection velocity as 1 km/s, a convecting flux tube can stay in the cusp for about 2 minutes. For a certain solar activity level, the maximum O⁺ outflow rate is reduced with a factor of ~10 at the winter solstice, when the footprint near the cusp is under dark conditions, compared to the summer solstice and equinox, when the cusp is under sunlit conditions. The solar activity level also strongly affects the maximum O⁺ outflow rate (with a factor of 10 or more). O⁺ density and flux at high altitudes are controlled mostly by acceleration due to BBELF wave, and the amount of O⁺ at altitudes where acceleration due to wave is effective under initial conditions is important for O⁺ density and flux at high altitudes in the polar cap.