Quasi‐monochromatic waves with an electrostatic nature in the lower hybrid frequency range have been identified in the plasma sheet boundary layer at X GSM =−49R e and −69R e by the wave‐form observations in a band 0–25 Hz from the double probe onboard the GEOTAIL spacecraft. Simultaneous measurements of low energy ions also indicate that the wave coincides with the transition of the ion‐energy from 0.1 keV/e to 10 keV/e.
The present study observationally examines relationship between Pi2 pulsations and the bursty bulk flow (BBF) in the plasma sheet. At a Pi2 onset of August 14, 1996, the GEOTAIL satellite and the GOES8 geosynchronous satellite were aligned in the X direction observing transient signatures. Those signatures were examined by referring to a ground low‐latitude Pi2 wave detected at the same meridian as GOES8. In the present event, a BBF started prior to the ground Pi2 onset, but it was preceded by a Pi2 onset at GOES8. It is also found that ground Pi2 signatures were correlated much better with geosynchronous Pi2 signatures than with perturbations of the plasma sheet flow velocity measured at GEOTAIL. These results strongly suggest that the BBF was not the cause of the low‐latitude Pi2 observed in the present event.
Compressional Pc 3 magnetic pulsations and accompanying electric field oscillations were observed by the GEOTAIL satellite in the dayside magnetosphere on October 17–18, 1992. When interpreted in terms of MHD wave modes, the oscillations in the fields are consistent with fast magnetosonic waves propagating Earthward. This result lends strong support to the view that ULF waves generated near the quasi‐parallel portion of the bow shock propagate into the magnetosphere and are observed as compressional Pc 3 pulsations in the dayside magnetosphere. The Earthward component of Poynting flux associated with the pulsations is ∼ 5 × 10 −8 W/m².
We present observational characteristics of the spatially quasiperiodic signatures of plasma and electric and magnetic fields observed in the poleward boundary of the morningside auroral oval by two polar‐orbiting satellites: Akebono and DMSP F9. The two satellites observed the proton discrete signatures at different altitudes (∼5000 km (Akebono) and ∼800 km (DMSP F9)) during nearly the same intervals. The data indicate that the ion (proton) signatures repetitively appeared and had a good correlation with occurrence of spiky electrons associated with upward components of small‐scale field‐aligned currents and variations of electric fields. We conclude that the repetitive (quasiperiodic) proton signatures had spatially energy‐dispersed signatures, which were not due to transient effect, on the basis of a comparison of the simultaneous observations at the different altitudes. Characteristic energy of each dispersed trace decreased with decreasing latitude, and the energy‐dispersed signatures frequently overlapped each other. A global plasma convection reversal often occurred during the quasiperiodic proton signatures. Sequential observations show that the region with these proton signatures was latitudinally wide and extended significantly to higher latitudes under northward interplanetary magnetic field conditions. It is plausible that instabilities in the tail‐flank boundary of the magnetosphere, represented by the Kelvin‐Helmholtz instability, are driven by the interaction between the solar wind and the central plasma sheet and then could produce the precipitating ions and the electrons accompanied by the variations of the electric and magnetic fields.
A prolonged period of B y > 0 dominated IMF conditions was monitored by WIND on Dec., 18–19, 1994. Observations on convection over the southern polar cap in the middle of this period (IMF B z ∼ 0) were available from AKEBONO. Detection of the well‐known dawn‐to‐dusk flow observing simultaneously energy‐dispersed ions in the cusp strongly indicates that the field lines reconnected at the dayside were azimuthally accelerated. GEOTAIL happened to be in the duskside flank at (X GSM , Z GSM ) ∼ (−15 ∼ −23, −1 ∼ −7)R E . The GEOTAIL data not only prove that this near‐tail flank region in the southern hemisphere is filled with azimuthally accelerated flux tubes that are loaded with solar wind plasma, but they also show that O + ions are transported tailward along these field lines. The latter is a new finding which suggests a route for transporting O + ions from the ionosphere to the magnetotail.
Akebono (Exos D) observations demonstrate that polar cap arcs sometimes have a fine structure, that is, multiple (double or triple) arcs with spacing of a few tens of kilometers. The multiple polar cap arcs are dominantly observed in the nightside polar cap region, suggesting that low background conductance favors the appearance of the structured arcs. A relationship between the spacing and the average energy of the precipitating electrons is investigated. Results show that a higher energy leads to a wider spacing. Akebono observations also show the existence of a downward current region embedded between upward current regions (arcs). Comparison of the observations with results from a coupled magnetosphere‐ionosphere Sun‐aligned arc model is made, which shows good qualitative agreement between the modeling and observational results on the spacing‐energy dependence and the effect of background ionospheric conductance.
Abstract MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) is one of the scientific instruments onboard the SELENE (SELenological and ENgineering Explorer) satellite. PACE consists of four sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measure the distribution function of low-energy electrons below 15 keV, while IMA and IEA measure the distribution function of low energy ions below 28 keV/q. Each sensor has a hemispherical field of view. Since SELENE is a three-axis stabilized spacecraft, a pair of electron sensors (ESA-S1 and S2) and a pair of ion sensors (IMA and IEA) are necessary for obtaining a three-dimensional distribution function of electrons and ions. The scientific objectives of PACE are (1) to measure the ions sputtered from the lunar surface and the lunar atmosphere, (2) to measure the magnetic anomaly on the lunar surface using two ESAs and a magnetometer onboard SELENE simultaneously as an electron reflectometer, (3) to resolve the Moon-solar wind interaction, (4) to resolve the Moon-Earth’s magnetosphere interaction, and (5) to observe the Earth’s magnetotail.
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