[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-P05] Energization of outflowing O⁺ ions at the high-latitude boundaries

*小池 春人¹、山内 正敏 ²、Nilsson Hans²、田口 聡¹、Dandouras Iannis ³ (1.京都大学大学院理学研究科地球惑星科学専攻、2.スウェーデン王立宇宙物理研究所、3.IRAP, Toulouse)

キーワード：O+アウトフロー、高緯度磁気圏境界層、O+加速、Cluster 衛星

We studied how the outflowing O⁺ ions change their energy near the high-latitude magnetopause using Cluster Ion Spectrometery (CIS) data. We first identified clear O⁺ outflowing beam events, i.e., increased counts by more than one order of magnitude in a narrow energy range flowing along the magnetic field using both energy-time and pitch angle-time spectrograms. During 2001-2004 we found more than 50 such events. In most cases, the energy of the beam gradually increased with distance from the Earth due to the centrifugal acceleration as well as heating by waves. The wave interaction is irregular, making the beam energy fluctuate in time (which could be correspond to changes in longitude/latitude, but primarily in altitude).

As a new feature, additional sudden increases in the beam energy were frequently observed at the boundary between the lobe and magnetopause boundary layer. Such jumps in the O⁺ outflow energy are also found in many traversals from the magnetosphere into the magnetosheath, and in some cases, to beyond few tens of keV, which is the upper limit of the CIS instrument. It suggests that the total amount of O⁺ escaping into the magnetosheath can be higher than observed by the CIS instrument. In this presentation, we classify the location of the energization and examine the relation to the interplanetary magnetic field conditions and local magnetic field topology.