Abstract. A monoenergetic drop-off of ions around 10 keY, which we term as "ion drop-off band" (IDB) in this paper, has been observed by Akebono. The IDB is identified as a sharp and deep dip at about 10 keV in ion spectra, which is usually observed at latitudes below the discrete auroral region over several degrees or more. As the ion motion of this energy in this inner part of the magnetosphere is basically described by the adiabatic theory, we have numerically traced the ion drift trajectories. From the results, it is proposed that the lower-energy boundary of the drop-off demarcates the open/closed character of the drift orbits, only below which continuous supply from the magnetotail is present. This model explains the energy, local time, and latitudinal extent of IDB as well as the formation of its poleward edge very well.

Abstract.The Akebono satellite has often observed the drop-off of polar rain flux near the polar cap boundary. The energy of the cutoff frequently showed decreasing trend with decreasing latitude. In this paper, we propose a model in which the drop-off is explained by disruption of the earthward polar rain flux at the X line in the tail. This model also predicts the behavior of the polar rain in the distant tail: The polar rain flux, usually bidirectional in the tail lobe, should become unidirectional near the plasma sheet boundary, as it is directed tailward (earthward) on the Earth (tail) side of the X line. Such a unidirectional polar rain layer has been newly detected by the Geotail satellite at X6SM ----40RE to --200RE recently. Modeling this new feature of the polar rain is the main purpose of this study. The proposed model also predicts a relation between the direction of the polar rain flux in this layer and the direction of ion bulk flow in the adjacent plasma sheet. The Geotail data show a good agreement with this prediction. Being convinced that the model is reasonable, the position of the X line relative to the satellite has been derived. It is shown by the Geotail survey over a wide range in GSM X that the neutral line formation occurs most frequently at X6SM = --50RE to --150RE.

We studied the cosmological constraints on Galileon gravity obtained from observational data of the growth rate of matter density perturbations, the supernovae Ia (SN Ia), the cosmic microwave background (CMB), and baryon acoustic oscillations (BAO). For the same value of the energy density parameter of matter Ω m,0 , the growth rate f in Galileon models is enhanced relative to the ΛCDM case, because of an increase in Newton's constant. The smaller the Ω m,0 , the more the growth rate is suppressed. Therefore, the best fit value of Ω m,0 in the Galileon model, based only on the growth rate data, is quite small. This is incompatible with the value of Ω m,0 obtained from the combination of SN Ia, CMB, and BAO data. On the other hand, in the ΛCDM model, the values of Ω m,0 obtained from different observational data sets are consistent. In the analysis presented in this paper, we found that the Galileon model is less compatible with observations than the ΛCDM model. This result seems to be qualitatively the same in most of the generalized Galileon models in which Newton's constant is enhanced.

Abstract. The strahl component of solar wind electrons, which constitutes fieldaligned electron heat flux running away from the Sun, is a strong candidate for the origin of the polar rain. We investigate the entry process of the strahl electrons into the distant-tail magnetosphere and discuss topologies of Earth's field lines in this paper. The Geotail satellite has often observed either gradual or abrupt transitions from the magnetosheath electrons to the bidirectional lobe electrons at the magnetopause. In some cases, the strahl

Abstract. Intermittent enhancements of lobe ions in density and velocity were observed by the GEOTAIL spacecraft in the distant magnetotail (-•100-200 RE). They were observed after the passage of plasmoids, accompanying south-to-north bipolar variations in Bz, which are opposite in polarity to those observed with plasmoids or traveling compression regions. The peaks in the ion density occurred when Bz changed from south to north (i.e., when Bz = 0). To explain these observations, a model is presented in which the magnetotail shrinks behind a plasmoid. It is suggested that after the formation of a plasmoid the near-Earth neutral line runs tailward following the plasmoid. The delay between the plasmoid passage and the ion enhancement observed by the same spacecraft is -•5-70 min, depending on as yet unknown reasons.