齋藤 義文

We have developed circular one-dimensional position-sensitive time-of-flight microchannel plate (MCP) detector for space plasma measurements. The MCP detector is equipped with a 354.375 degrees resistive anode and a grid anode for obtaining position and timing signals simultaneously from one start event. The resistive anode provides high-resolution and continuous position sensing with two electronic channels alone. The grid anode generates start signals with pulse width of 1 ns for time-of-flight measurements. The resistive anode is formed on an alumina substrate which is installed behind the output side of the MCP plates. The grid anode is installed between the MCP plates and the resistive anode for the simultaneous detection of position and start signals. Stop signals are obtained from stop events by a center anode formed on the alumina substrate behind the MCP plates. On the basis of the test experiments, we have evaluated that the MCP detector functionally deals with the position and timing signals. (C) 2008 American Institute of Physics.

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.

編隊飛行衛星システムによる観測が地球磁気圏の研究に適した手段であることはよく知られている事実である。JAXAの将来磁気圏探査ミッションもこの編隊飛行衛星技術の利点を最大限に生かそうと議論を重ねてきた。SCOPEはそのミッション名であり、5機から成る探査機群が1kmから1000kmの衛星間距離に至るまで協調して観測を遂行する計画である。その観測を成り立たせる基盤技術になる衛星間の通信方式として我々はS帯を用いた時分割多重方式の衛星間ネットワークを推進してきた。このミッションは衛星間通信に観測データの高速伝送のみならず、衛星間の測距、動作クロックの衛星間同期機能を持たせる要求があり、シミュレータによる実証を通じて我々の提案の要求への充足と有効性を証明した。

The plasma number density in the plasma sheet depends on the solar wind number density and the north-south component of interplanetary magnetic field (IMF Bz) with the time lag of several hours. We examined such dependences as functions of (X, Y) coordinates in the near-Earth plasma sheet by fitting observations of plasma sheet and solar wind to an empirical model equation. We explored shortest and longest response time lags to IMF B z. by optimizing the correlation coefficient of fit. Analyses were conducted separately for northward and southward IMF dominant conditions. The dependence of plasma sheet number density on solar wind number density is stronger in the near-tail region (r &gt 20 RE) under the southward IMF dominant condition. The dependence has weak dawn-dusk asymmetry under the southward IMF dominant condition, whereas it is stronger in the dusk flank under the northward IMF dominant condition. The dependence on IMF Bz is globally positive under the northward IMF dominant condition, whereas the dependence is negative in the near-Earth premidnight region under the southward IMF dominant condition. Both shortest and longest time lags increase from the mid-tail to the near-Earth premidnight region under the southward IMF dominant condition. On the other hand, the shortest (longest) time lag increases antisunward (sunward) along flanks under the northward IMF dominant condition. These features can be explained in terms of reconnection and Kelvin-Helmholtz diffusion mechanisms for entry of magnetosheath plasma into the plasma sheet and electric and magnetic drift transport in the plasma sheet. Copyright 2007 by the American Geophysical Union. Angelopoulos, V., C. F.

We present the unsaturated peak profile of the giant flare from SGR 1900 + 14 on 1998 August 27. This was obtained by the particle counters of the Low Energy Particles instrument on board the Geotail spacecraft. The observed peak profile revealed four characteristic features: an initial steep rise, an intermediate rise to the peak, an exponential decay, and a small hump in the decay phase. From this light curve, we found that the isotropic peak luminosity was ergs s(-1)and that the total energy was ergs s(-1) ( keV), assuming 46 44 2.3 *10 4.3 * 10 E >= 50 that the distance to SGR 1900 + 14 is 15 kpc and that the spectrum is optically thin thermal bremsstrahlung with keV. These values are consistent with the previously reported lower limits derived from Ulysses and kT p 240 Konus- Wind observations. A comparative study of the initial spikes of the SGR 1900 + 14 giant flare in 1998 and of the SGR 1806 -20 giant flare in 2004 is also presented. The timescale of the initial steep rise shows a magnetospheric origin, while the timescale of the intermediate rise to the peak indicates that it originates from crustal fracturing. Finally, we argue that the four features and their corresponding timescales provide us with a clue to identify extragalactic soft gamma- ray repeater giant flares among short gamma- ray bursts.

Abstract. To investigate the cold plasma sheet formation under northward IMF, we study the temperature anisotropies of electrons and two-component protons observed by the Geotail spacecraft. The two-component protons, which are occasionally observed in the dusk plasma sheet near the low-latitude boundary, are the result of spatial mixing of the hot protons of the magnetosphere proper and the cold protons from the solar wind. Recent research focusing on the two-component protons reported that the cold proton component at times has a strong anisotropy, and that the sense of the anisotropy depends on the observed locations. Since electrons have been known to possess a strong parallel anisotropy around the low-latitude boundary layer, we compare anisotropies of electrons and protons to find that the strengths of parallel anisotropies of electrons and the cold proton component are in good correlation in the tail flank. The parallel anisotropy of electrons is stronger than that of the cold proton component, which is attributed to selective heating of electrons. We further find that the strengths of the parallel anisotropies in the tail flank depend on the latitudinal angle of the IMF; strong parallel anisotropies occur under strongly northward IMF. We discuss that the Kelvin-Helmholtz vortices, which developed under strongly northward IMF, and the resultant magnetic reconnection therein may lead to the strong parallel anisotropies observed in the tail flank.

[1] We present first results of a novel technique for producing a two-dimensional (2-D) map of the velocity field from single-spacecraft observations of the bulk plasma parameters and magnetic field. For flow transverse to a unidirectional magnetic field, the MHD equations of motion can be reduced to a Grad-Shafranov- type (GS-type) equation for the stream function (Sonnerup et al., 2006), provided that the plasma structure is 2-D and time-independent when seen in its proper frame. We show how this equation can be used to recover the flow field in regions surrounding a spacecraft path, as was first done in the GS reconstruction of the magnetic field by Sonnerup and Guo ( 1996). The new method is benchmarked by use of an exact solution of the GS-type equation and further by use of synthetic data from 2-D MHD simulations of the Kelvin-Helmholtz instability (KHI). Streamline maps of reasonable accuracy can be generated even when temporal evolution during the KHI development expected at the flank magnetopause is present. Application of the technique to a Geotail encounter with a train of KH waves in the low-latitude flank boundary layer indicates that a chain of vortices ( each of size similar to 3 R-E by 1 R-E) existed and moved tailward along the magnetopause.

We present first results of a novel technique for producing a two-dimensional (2-D) map of the velocity field from single-spacecraft observations of the bulk plasma parameters and magnetic field. For flow transverse to a unidirectional magnetic field, the M HD equations of motion can be reduced to a Grad-Shafranov-type (GS-type) equation for the stream function (Sonnerup et al., 2006), provided that the plasma structure is 2-D and time-independent when seen in its proper frame. We show how this equation can be used to recover the flow field in regions surrounding a spacecraft path, as was first done in the GS reconstruction of the magnetic field by Sonnerup and Guo (1996). The new method is benchmarked by use of an exact solution of the GS-type equation and further by use of synthetic data from 2-D MHD simulations of the Kelvin-Helmholtz instability (KHI). Streamline maps of reasonable accuracy can be generated even when temporal evolution during the KHI development expected at the flank magnetopause is present. Application of the technique to a Geotail encounter with a train of KH waves in the low-latitude flank boundary layer indicates that a chain of vortices (each of size ∼3 RE by 1 RE) existed and moved tailward along the magnetopause. Copyright 2007 by the American Geophysical Union.

We have successfully detected solar neutrons at ground level in association with the X17.0 solar flare that occurred on 2005 September 7. Observations were made with the solar neutron telescopes and neutron monitors located in Bolivia and Mexico. In this flare, large fluxes of hard X-rays and γ-rays were observed by the GEOTAIL and the INTEGRAL satellites. The INTEGRAL observations include the 4.4 MeV line γ-rays of 12 C. The data suggest that solar neutrons were produced at the same time as these hard electromagnetic radiations. We have however found an apparent discrepancy between the observed and the expected time profiles. This fact suggests a possible extended neutron emission. © 2006 COSPAR.

A microchannel plate (MCP) assembly has been used as an ion detector in the low energy particle (LEP) instrument onboard the magnetospheric satellite GEOTAIL. Recently the MCP assembly has detected gamma rays emitted from an astronomical object and has been shown to provide unique information of gamma rays if they are intense enough. However, the detection efficiency for gamma rays was not measured before launch, and therefore we could not analyze the LEP data quantitatively. In this article, we report the gamma-ray detection efficiency of the MCP assembly. The measured efficiencies are 1.29%±0.71% and 0.21%±0.14% for normal incidence 60 and 662 keV gamma rays, respectively. The incident angle dependence is also presented. Our calibration is crucial to study high energy astrophysical phenomena by using the LEP. © 2007 American Institute of Physics.

To investigate the cold plasma sheet formation under northward IMF, we study the temperature anisotropies of electrons and two-component protons observed by the Geotail spacecraft. The two-component protons, which are occasionally observed in the dusk plasma sheet near the low-latitude boundary. are the result of spatial mixing of the hot protons of the magnetosphere proper and the cold protons from the solar wind. Recent research focusing on the two-component protons reported that the cold proton component at times has a strong anisotropy, and that the sense of the anisotropy depends on the observed locations. Since electrons have been known to possess a strong parallel anisotropy around the low-latitude boundary layer, we compare anisotropies of electrons and protons to find that the strengths of parallel anisotropies of electrons and the cold proton component are in good correlation in the tail flank. The parallel anisotropy of electrons is stronger than that of the cold proton component, which is attributed to selective heating of electrons. We further find that the strengths of the parallel anisotropies in the tail flank depend on the latitudinal angle of the IMF; strong parallel anisotropies occur under strongfly northward IMF. We discuss that the Kelvin-Helmholtz vortices, which developed under strongly northward IMF, and the resultant magnetic reconnection therein may lead to the strong parallel anisotropies observed in the tail flank.

To further our understanding of the solar wind entry across the magnetopause under northward IMF, we perform a case study of a duskside Kelvin-Helmholtz (KH) vortex event on 24 March 1995. We have found that the protons consist of two separate (cold and hot) components in the magnetosphere-like region inside the KH vortical structure. The cold proton component occasionally consisted of counter-streaming beams near the current layer in the KH vortical structure. Low-energy bidirectional electron beams or flat-topped electron distribution functions in the direction along the local magnetic field were apparent on the magnetosphere side of the current layer. We discuss that the bidirectionality of the electrons and the cold proton component implies magnetic reconnection inside the KH vortical structure. In addition, we suggest selective heating of electrons inside the vortical structure via wave-particle interactions. Comparing temperatures in the magnetosphere-like region inside the vortical structure with those in the cold plasma sheet, we show that further heating of both the electrons and the cold proton component is taking place in the cold plasma sheet or on the way from the vortices to the cold plasma sheet.

Through the effort to obtain clues toward understanding of transport of cold plasma in the near-Earth magnetotail under northward IMF, we find that two-component protons are observed in the midnight plasma sheet (&amp minus 10&gt XGSM&gt &amp minus 30 &gt i&gt RE, |YGSM| &lt 10 RE) under northward IMF by the Geotail spacecraft. Since the two-component protons are frequently observed on the duskside during northward IMF intervals but hardly on the dawnside, those found in the midnight plasma sheet are thought to come from the dusk flank. The cold proton component in the midnight region occasionally has a parallel anisotropy, which resembles that in the tail flank on the duskside. The flows in the plasma sheet with two-component protons were quite stagnant or slightly going dawnward, which supports the idea that the observed two-component protons in the midnight region are of duskside origin. Because the two-component protons in the midnight plasma sheet emerge under strongly northward IMF with the latitudinal angle larger than 45 degrees, and because the lag from the strongly northward IMF to the emergence can be as short as a few hours, we suggest that prompt plasma transport from the dusk to midnight region occurs under strongly northward IMF. We propose that the dawnward flows result from viscous interaction between the high-latitude portion of the plasma sheet and the lobe cell. Another candidate for plasma transport process from the dusk to the midnight region is turbulent flow due to vortical structures of the Kelvin-Helmholtz instability that developed around the dusk low-latitude boundary under strongly northward IMF. In addition, we also suggest that gradual cooling of hot protons under northward IMF is a global phenomenon in the near-Earth magnetotail.

In search for clues towards the understanding of the cold plasma sheet formation under northward IMF, we study the temperature anisotropy of the two-component protons in the plasma sheet near the dusk low-latitude boundary observed by the Geotail spacecraft. The two-component protons result from mixing of the cold component from the solar wind and the hot component of the magnetospheric origin, and may be the most eloquent evidence for the transport process across the magnetopause. The cold component occasionally has a strong anisotropy in the dusk flank, and the sense of the anisotropy depends on the observed locations: the parallel temperature is enhanced in the tail flank while the perpendicular temperature is enhanced on the dayside. The hot component is nearly isotropic in the tail while the perpendicular temperature is enhanced on the dayside. We discuss possible mechanism that can lead to the observed temperature anisotropies.

We examine the spatial evolution of charge clouds emitted by microchannel plates (MCPs). A model of this evolution is presented, along with a comparison to experimental results. We also present an experimental method to measure the charge cloud radius in which the radial charge cloud distribution is assumed to be Gaussian. When a charge cloud is released from the MCP, its initial size is determined by the number and distribution of excited channels. The size of the charge cloud is examined as a function acceleration voltage, distance between MCP and anode, and MCP bias voltage. Since electrons released from the MCP have various initial energies and angular divergence, the charge cloud size increases as it travels away from the MCP. Space charge effects also contribute to the growth of the charge cloud. The experimental results are in close agreement with our model, which includes these effects. From experiment, we also derive an approximate expression for charge cloud radius as a function of acceleration voltage and distance between MCP and anode. This expression can be used for the practical design and optimization of a position sensing system comprised of multiple anodes. © 2007 American Institute of Physics.

SELenological and ENgineering Explorer (SELENE) is a Japanese lunar orbiter that will be launched in 2007. The main purpose of this satellite is to study the origin and evolution of the Moon by means of global mapping of element abundances, mineralogical composition, and surface geographical mapping from 100 km altitude. Plasma energy Angle and Composition Experiment (PACE) is one of the scientific instruments onboard the SELENE satellite. 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 electron spectrum analyzers (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. PACE consists of four sensors: ESA-S1, ESA-S2, ion mass analyzer (IMA), and ion energy analyzer (IEA). ESA-S1 and S2 measure the three-dimensional distribution function of low energy electrons below 15 keV, while IMA and IEA measure the three-dimensional distribution function of low energy ions below 28 keV/q.

We have statistically studied magnetotail variations associated with expansion onsets for storm and nonstorm time substorms, using Geotail data. Here storm time was defined as Sym-H ≤ -30 nT. It was found that there are no qualitative differences in magnetotail variations between these two types of substorms, although the energy accumulation and the dipolarization tend to be more significant during storm time substorms. The statistical results evidently show that the magnetic reconnection and the dipolarization do occur in the magnetotail around onset for both types of substorms, suggesting that storm and nonstorm time substorms are caused by the same mechanism. Copyright 2006 by the American Geophysical Union.

The 'whistler critical Mach number', Mcrit,w is one of the dimensionless parameters that characterizes collisionless shocks. Originally, it was introduced to indicate the critical point above which whistler waves do not propagate upstream. Indeed our analysis of Geotail data at the Earth's bow shock shows intense whistler waves in the sub-critical regime, MA &lt Mcritw but not in the super-critical regime. In this paper, we further report that Mcritw seems to regulate the electron acceleration efficiency at the shocks. At the shock transition layer it is found that the spectral index Γ of electron energy spectra defined by F(E) ∝ E-Γ is distributed between 3.5 and 5.0 in the sub-critical regime, while the hardest energy spectra with Γ = 3-3.5 are detected in the super-critical regime. We discuss a possible relationship between Mcritw and the electron acceleration. Copyright 2006 by the American Geophysical Union.

Strong signals of neutral emissions were detected in association with a solar flare that occurred on 2005 September 7. They were produced by both relativistic ions and electrons. In particular, relativistic neutrons were observed with the solar neutron telescopes (SNTs) located at Mount Chacaltaya in Bolivia and Mount Sierra Negra in Mexico and with neutron monitors (NMs) at Chacaltaya and Mexico City with high statistical significances. At the same time, hard X-rays and γ-rays, which were predominantly emitted by high-energy electrons, were detected by the Geotail and the INTEGRAL satellites. We found that a model of the impulsive neutron emission at the time of the X-ray/ γ-ray peak can explain the main peaks of all the detected neutron signals, but failed to explain the long tailed decaying phase. An alternative model, in which the neutron emission follows the X-ray/γ-ray profile, also failed to explain the long tail. These results indicate that the acceleration of ions began at the same time as the electrons but that ions were continuously accelerated or trapped longer than the electrons in the emission site. We also demonstrate that the neutron data observed by multienergy channels of SNTs put constraints on the neutron spectrum. © 2006. The American Astronomical Society. All rights reserved.

We have tested APDs (Type spl 3989 and Z7966, Hamamatsu Photonics K.K.) using an electron beam. The Z7966, which has a depletion layer of 10 μ m, is firstly focused on and tested in our former paper [K. Ogasawara, K. Asamura, T. Mukai, Y. Saito, Nucl. Instr. and Meth. A 545(3) (2005) 744] for the energy range of 5-20 keV. The result shows that the pulse height distribution of the APD signal exhibits a significant peak for electrons with energies above 8 keV, and positions of their peaks show a good linearity. The condition of the peak production at energies below 8 keV was attributed to the thickness of the dead layer on the surface of APDs. Now we have tuned up our electron acceleration system up to 40 keV, and tested Z7966 by electrons of higher energies. The result shows that the output pulse height distributions of this Z7966 were distorted over 30 keV. In order to examine the distortion of pulse height distributions, we have made a Monte Carlo numerical simulation of particle transport inside the APD. The result shows that the highest energy limit is expected to be determined by the thickness of the depletion layer inside the APD. Therefore, we have tried an APD type spl 3989, which has a thicker depletion layer (30 μ m) and a thinner dead layer. As is expected, the spl 3989 responded to 2-40 keV electrons with fine peaks in the output pulse height distributions. The energy resolution was lower than 1 keV for 2-20 keV electrons, and 5 keV for 40 keV electrons. The linearity of the response was also good. According to the Monte Carlo simulation, electrons up to about 60 keV are expected to be well detectable. © 2006 Elsevier B.V. All rights reserved.

Recent numerical simulations suggest that as soon as the Kelvin-Helmholtz instability (KHI) has grown nonlinearly to form a highly rolled-up vortex, plasma mixing is inevitably achieved within the vortex. Identification of rolled-up vortices by in situ measurements is therefore an important task as a step to establish the mechanism by which solar wind plasmas enter the magnetosphere and to understand conditions under which the vortices form. In the present study we show that the rolled-up vortices are detectable even from single-spacecraft measurements. Numerical simulations of the KHI indicate that in the rolled-up vortex the tailward speed of a fraction of low-density, magnetospheric plasmas exceeds that of the magnetosheath flow. This feature appears only after a vortex is rolled up and thus can be used as a marker of roll-up. This signature was indeed found in the Cluster multispacecraft measurements of the rolled-up vortices at the flank magnetopause. By use of this marker, we have searched for events consistent with the roll-up from Geotail observations showing quasi-periodic plasma and field fluctuations in the flank low-latitude boundary layer (LLBL) under northward interplanetary magnetic field (IMF), presumably associated with KH waves. The survey shows that such rolled-up events do occur on both dawn and dusk flanks and are not rare for northward IMF conditions. In addition, in all the rolled-up cases, magnetosheath-like ions are detected on the magnetospheric side of the boundary. These findings indicate that the KHI plays a nonnegligible role in the formation of the flank LLBL under northward IMF. Copyright 2006 by the American Geophysical Union.

JAXA is currently planning the next generation magnetosphere observation mission called "SCOPE"(cross-Scale Coupling in Plasma universE). SCOPE aims at observing the Earth's magnetotail with 5 satellites flying in formation to fully resolve the temporary and spatial distribution of the magnetospheric phenomena. For this observation, the clock synchronization and relative distance measurement between the spacecrafts are essential. This paper describes an onboard relative ranging and clock synchronization algorithm, which applies a simplified formulation, using two-way and three-way phase differences as the filter inputs to construct the onboard system suit to the SCOPE mission.

According to the previous satellite observation (Mariner10 fly-by), Mercury has a magnetosphere with its own strong intrinsic magnetic field. In order to elucidate the detailed plasma structure and dynamics around Mercury, an orbiter BepiColombo Mercury magnetospheric orbiter (MMO) is planned to be launched in the timeframe between 2012 and 2013 as a joint mission between ESA and ISAS/JAXA. For measuring low energy ions, two sensors Mercury ion analyzer (MIA) and Mercury ion mass spectrum analyzer (MSA) will be onboard the MMO. MIA measures energy spectrum (5 eV/q-30 keV/q) of ions around Mercury as well as solar wind ions while MSA measures mass discriminated energy spectrum (5 eV/q-40 keV/q) of ions around Mercury. MIA is a toroidal top-hat type electrostatic analyzer with dynamic range as wide as 106, while MSA consists of a similar electrostatic analyzer followed by a timeof-flight section for mass discrimination. In order to realize the wide dynamic range, electrical sensitivity control and attenuation grid are applied at the same time. The thermal environment around Mercury is so severe that the thermal design of the instrument is very important. Each sensor should have its own thermal shield in order to minimize the thermal input and to maintain the sensor temperature within an acceptable range.

Geoscientists in the Asia-Oceanian Region and elsewhere increasingly share and articulate a strong vision in advancing geosciences through closer cooperation a vision that provided the impetus for the open Forum on collaborative research opportunities in solar terrestrial and planetary science (ST-PS) missions. This report captures the information presented and discussed at the Forum, including a synopsis of current, planned, and proposed ST-PS missions led by various Asia-Oceanian countries, in the context of the potential opportunities that these missions offer from a geoscience perspective.

In this paper we examined the continuous motions of a near-Earth neutral line during the recovery phase of the 5 October 2000 substorm. Estimation was based on the PSBL ion beam model proposed by Onsager (1991) and the Geotail observations. Estimated distances from the Earth ranged from 20 to 60 RE and retreated tailward at velocities of 250 and 300 km/s. This event initiated with the arrival of solar wind discontinuity. Simultaneous observations of electromagnetic field and electrons indicate the existence of earthward propagating waves associated with field-aligned currents. Based on these observations, we suggest that the source of the PSBL ion beams was the retreating near-Earth neutral line formed by the compression of the magnetosphere. Two scenarios of near-Earth neutral line motion in the tail dynamics are also proposed. One is the formation of plural neutral lines to create a long plasmoid. The other is the oscillation of one neutral line between the near-Earth region and the mid-tail stagnant plasmoid.

Shock accelerated nonthermal particles are thought to contribute to modify the shock structure. Here we present two such cases at two strong interplanetary shocks in 1994 and 2003, and try to see how the nonlinear feature depend on the shock parameters, such as Mach number and shock angle. © 2006 COSPAR.

This paper reports on properties of energetic electrons observed by the Auroral Particle Detector (APD) on board the sounding rocket S-310-35, which was launched from Andøya Rocket Range, Norway, at 0033:00 UT on 13 December 2004 during the DELTA campaign. The APD was designed to measure energy spectra of energetic electrons in the range of 3.5 to 65 keV every 10 ms using avalanche photodiodes. The measurement was done at altitudes of 90-140 km (apogee height of the rocket flight), which corresponded to the collisional interaction region of precipitating electrons with the atmospheric constituents. The overall profile of energetic electron precipitations was consistent with auroral images taken from the ground. The downward fluxes almost always exceeded those of upward electrons, and the ratio of downward to upward fluxes increased with energy and also with altitude. This is reasonably understood in terms of the effect of collisions between the energetic electrons and the atmospheric constituents. An interesting feature in energy spectra of precipitating electrons is the existence of non-thermal electrons at higher energies, regardless of inside or outside of auroral arcs. In order to predict the incident downward spectra at the top of the atmosphere, we have applied an analytic method of Luhmann (1976) to evaluate the collisional effect on the electron spectra. As a result, most of the observed energy spectra of precipitating electrons are well expressed by kappa distributions with the thermal energy of a few hundreds of eV and kappa of 5-8, while the spectrum inside a strong arc is better fitted by the sum of a Maxwellian distribution on the lower energy side and a power law at higher energies. To the authors' knowledge, this is the first direct and reliable measurement of energy spectra of electrons in the 10-keV energy range in the auroral ionosphere. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS) The Seismological Society of Japan The Volcanological Society of Japan The Geodetic Society of Japan The Japanese Society for Planetary Sciences TERRAPUB.

We have developed a new electrostatic analyzer which enables medium energy (200 keVq) plasma particle measurements with full solid angle coverage. The design of the test model realizes the uppermost measurement energy of ∼200 keVq with applied high voltages of ±5 kV. Laboratory experiments with the test model analyzer show that its performance agrees with numerical simulations. The test model design is well suited for combination with a mass analysis unit, while our new design can also be applied to medium energy electron measurements. Medium energy ion/electron sensors with this new design will surely be appreciated for upcoming space missions that will observe hot/energetic plasma structures in the regions such as the inner magnetosphere or reconnection region. © 2006 American Institute of Physics.

The Earth's inner magnetosphere (inside 10 Re) is a region where particle energy increases to the relativistic energy range. This region is very important as a laboratory where high-energy particle acceleration can be directly measured in a dipolar field configuration, as well as for human activities in space including space weather prediction. Despite abundant in situ satellite measurements, this region has been "missing" because of several difficulties arising from the measurements, such as high-energy particle contamination of low-energy particle measurement, protection against the possible incidence of radiation belt particles on the satellite, and the difficulties of measuring three-dimensional particles over a broad energy range, from a few electron volts to more than 10 MeV. In this paper, we address important scientific topics and propose a possible configuration of small satellites termed Energization and Radiation in Geospace (ERG), which would provide new insights into the dynamics of the inner magnetosphere and strongly contribute to the International Living With a Star project. © 2005 COSPAR.

We show presence of a mini-magnetosphere above the Reiner Gamma magnetic anomaly (RGA) region in the solar wind, using Lunar Prospector magnetometer (MAG) measurement data. RGA is one of the strongest magnetic anomalies on the Moon. Two magnetic anomalies are found from six MAG datasets at 17-40 km altitudes in the lunar wake or the geomagnetic tail lobe and are well explained by a two-dipole model. When RGA was exposed to the solar wind plasma, two MAG datasets were obtained at 27-29 km altitudes. Although the magnetic anomalies survived against the plasma pressure, they were heavily distorted in comparison with the magnetic field of the two-dipole model. Flow directions and dynamic pressures of the solar wind plasma at those periods indicate that the distortions were caused by forming a mini-magnetosphere over the RGA region in the solar wind. Copyright 2005 by the American Geophysical Union.

We report on the performance of an Avalanche Photodiode (APD) produced by Hamamatsu Photonics Co. Ltd. (Type Z7966-20) for measurements of low energy electrons. We have set up an electron gun, which can generate a 1-20keV electron beam impinging onto the APD in a vacuum chamber. The result shows that the pulse height distribution (PHD) of the APD signal exhibits a significant peak for electrons with energies above 8keV, and the variation of the PHD peak shows a good linearity with the energy of incident electrons. The energy resolution is quite good, though it slightly depends on the electron energy. In the case of low-energies (lower than 10 keV), the pulse height distribution has a characteristic tail on the low energy side, and the energy resolution becomes a little worse. The position of the peak appears on a slightly lower channel than is expected from data at higher energies (near 20keV). Qualitatively, the low-energy tail is caused by the dead-layer on the surface of the device. The nonlinearity and the worse resolution of the peaks for higher energy electrons may have resulted from a space-charge effect due to created e-h pairs. For a quantitative understanding, we have made a Monte Carlo particle simulation of charge transport and collection inside the APD. (c) 2005 Elsevier B.V. All rights reserved.

[ 1] On 19 October 1995 the Geotail satellite skimmed along the quasi-perpendicular bow shock for more than 3 hours, and field-aligned ion beams (FABs) were continuously observed in the foreshock region. Also observed were 11 crossings with the bow shock where these FABs are thought to be generated. The upstream condition of the bow shock was in the state of low Mach number (M-A similar to 2.9) and low beta (beta similar to 0.02). By a detailed study of the evolution of the ion distribution across one of the crossings, we have found that leakage as origin of these ions from the magnetosheath is unlikely. Comparison of the observations with simulations suggests that FAB ions are generated by multiple interaction of incoming solar wind ions with the bow shock. We have then compared the FAB flux normalized by the solar wind flux, (F) over bar, with the shock angle theta(Bn) and have found that (F) over bar falls off rapidly just above theta(Bn) > 60 degrees, but it maintains significant level ((F) over bar similar to 0.01%) up to similar to 75 degrees.

Identifying co-rotating structures in solar wind enables us to predict solar wind variation at the Earth and, hence, geomagnetic disturbances. However, co-rotating structures during solar maximum are sometimes difficult to see. We correlated solar wind data obtained by two spacecraft, Nozomi heading towards Mars and ACE at the L1 point, from late 1999 through early 2002. There were intervals when the solar wind showed specific co-rotating structures even in the midst of the solar maximum, whereas no correlation was found during the other intervals. The coefficient was generally higher between Nozomi and ACE than for the 27-day recurrence at ACE, while there was some correlation, especially when the difference in longitude between the two spacecraft was less than 120°. Although frequency of occurrence of CMEs is partly responsible for the correlation, the results can be interpreted in terms of rapid changes in co-rotating high-speed streams from near-equatorial coronal holes at the solar maximum. © Springer 2005.

The massive flare of 27 December 2004 from the soft γ-ray repeater SGR 1806-20, a possible magnetar, saturated almost all γ-ray detectors, meaning that the profile of the pulse was poorly characterized. An accurate profile is essential to determine physically what was happening at the source. Here we report the unsaturated γ-ray profile for the first 600 ms of the flare, with a time resolution of 5.48 ms. The peak of the profile (of the order of 107 photons cm-2s-1) was reached ∼50 ms after the onset of the flare, and was then followed by a gradual decrease with superposed oscillatory modulations possibly representing repeated energy injections with ∼60-ms intervals. The implied total energy is comparable to the stored magnetic energy in a magnetar (∼1047 erg) based on the dipole magnetic field intensity (∼1015 G), suggesting either that the energy release mechanism was extremely efficient or that the interior magnetic field is much stronger than the external dipole field.

In order to open the new horizon of research in the plasma universe, SCOPE will perform formation flying multi-scale observations combined with high-time resolution electron detection and will enable data-based study on the key space plasma processes from the cross-scale coupling point of view. Key physics to be studied are magnetic reconnection under various conditions, shocks in space plasma, collisionless plasma mixing at the boundaries, and physics of current sheets embedded in complex magnetic geometries. The SCOPE mission is made up of the 5 spacecraft (s/c) formation put into the equatorial orbit with the apogee at 30Re (Re: earth radius). One of the s/c is a large mother ship which is equipped with a full suite of particle detector including ultra-high sampling cycle electron detector. Among other 4 small s/c one remains near (∼10 km) the mother ship and the s/c-pair will focus on wave-particle interaction utilizing inter-s/c communication. Others are used for wave-particle interaction study when the distance from the mother ship is small (∼100 km) and are used as the plasma monitors at ion-scales when the distance is larger (100-300 0km). There is lively on-going discussion on the SCOPE-M3 collaboration, which would certainly make the coverage over the scales of interest better and thus make the mission success to be attained at an even higher level.

The double probe technique is one of the standard techniques for in situ DC electric field measurements in tenuous plasmas, but it is known for its sensitiveness to the plasma environment around a spacecraft. In the present study we compare the double-probe electric fields obtained by Geotail/EFD-P with the convection electric fields - V× Bin various regions of the distant tail. We have found that the sensitivity (effective length of the double probes) varies as a function of the spacecraft potential, and the offset weakly depends on the electron temperature of ambient plasma. Using this result, an empirical calibration formula for the double-probe electric fields is obtained. © 2005 Elsevier B.V. All rights reserved.

Earthward and tailward perpendicular fast flows in the plasma sheet were studied and their differences in response to geomagnetic conditions and to interplanetary magnetic field (IMF) conditions are discussed. We first identified the plasma sheet from 3.5 years of Geotail plasma and magnetic filed observations between 8 and 32 REdown the tail. We then studied occurrence rates of fast flows during geomagnetically quiet and active intervals as identified by Kp and ASY indices, and during northward and southward IMF intervals. As a result, both earthward and tailward flows were observed more often during active or southward IMF intervals than during quiet or northward IMF intervals, as expected. On the other hand, we found that there is a difference between earthward and tailward flows: Dependences on geomagnetic conditions are more evident in tailward flows than in earthward flows. We further discuss that tailward flows indicate the substorm expansion phase better than earthward flows do. © 2005 Elsevier B.V. All rights reserved.

We present a case study of substorm-time magnetic field perturbations in high-altitude polar lobe and in the tail lobe, simultaneously observed by the POLAR and GEOTAIL satellites, together with ground-based CANOPUS observations and WIND solar-wind observations. During the growth phase, the magnetic field strength (Btotal) increased both in the polar lobe (observed by POLAR) and in the tail lobe (observed by GEOTAIL) this is ascribed to the pileup of dayside-reconnected field lines over the magnetopause. On the other hand, while Btotalat GEOTAIL decreased during the expansion phase, Btotalat POLAR did not start decreasing until ~35 min after the expansion onset. This absence of the field-decrease signature in the polar lobe for ~35 min could be attributed to dipolarization/compression of closed field line region of the nightside inner magnetosphere. This compression could offset the effect of the magnetic field decrease in the polar lobe, and would be absent in the open field line region of the tail lobe allowing GEOTAIL to detect the decrease in Btotalduring this ~35 min period. © 2005 Elsevier B.V. All rights reserved.

Whistler waves are considered to play an important role in the electron dynamics for the collisionless shock formation process at interplanetary shocks (IPSs). In this report, we analyze IPS events observed by GEOTAIL on 21 February 1994 and 15 July 2000, focusing on whistler wave properties in their upstream region extending the previous work of Shimada et al. (1999). In both events, we have identified the existence of whistler mode waves in the upstream region of the IPS as well as the tendency of the intensity increase toward the shock front. At the same time we have found the detailed features differing between these events: While the intermittent but clear wave bursts were found on 21 February 1994 event, the waves were more or less continuous on 15 July 2000 event. © 2005 Elsevier B.V. All rights reserved.

Recent studies have statistically shown that the magnetic reconnection site at substorm expansion onset is located in the magnetotail at X ∼ -20 R E on average. For a substorm event that occurred at ∼0153 UT on 2 July 1996, however, Geotail observed a series of tailward but slow flows with southward magnetic fields fairly close to the Earth at (X, Y) ∼ (-7, 9) RE. The flows had enhancements of the total pressure and the total magnetic field as well as bidirectional field-aligned low-energy electrons in their central part. We interpret these as signatures for tailward moving small plasmoids with scales of ∼0.5-3 RE. Considering that GOES-8 observed a dipolarization at (X, Y) ∼ (-4, 5) RE after the expansion onset, we estimate that the magnetic reconnection occurred between the Geotail and GOES-8 positions. UVI auroral images from Polar and ground magnetic field data show that this substorm, initiated at ∼20 hours MLT and ∼64° magnetic latitude, was not very intense, and the period examined was not during an intense storm. The southward interplanetary magnetic field (IMF) was not very large, while the large duskward IMF persisted for more than 12 hours, before the onset as well as the somewhat large solar wind dynamic pressure. It seems likely that the global ionospheric convection was not very strong. Locally enhanced convection and auroral oval expansion due to the large IMF By and the solar wind dynamic pressure might lead to the initiation of the magnetic reconnection much closer to the Earth than usual. Copyright 2005 by the American Geophysical Union.

[1] To understand magnetotail dynamics, it is essential to determine where magnetic reconnection takes place in the near-Earth magnetotail during substorms. The Geotail spacecraft thoroughly surveyed the near-Earth plasma sheet at radial distances of 10-31 RE during the years 1995-2003. Thirty-four clear reconnection events were identified using the criterion of strong electron acceleration. Various solar wind parameters prior to each reconnection event were examined in order to find the factor controlling the location of the magnetic reconnection site in the magnetotail. The same analyses were carried out for fast tailward flow events. The most important factor was determined to be the solar wind energy input, which can be expressed by - Vx × Bs, where Vx is the x component of the solar wind velocity and Bs is the southward component of the interplanetary magnetic field. It is likely that higher efficiency of energy input, rather than the total amount of energy input, primarily controls the location of magnetic reconnection magnetic reconnection takes place closer to the Earth when efficiency of energy input is higher. The effect of solar wind dynamic pressure is minor. The present result suggests that the tail magnetic reconnection location during substorms is controlled by solar cycle variations in the solar wind. Copyright 2005 by the American Geophysical Union.

Magnetic field observations made during 28 October to 1 November 2003, which included two fast interplanetary coronal mass ejections (ICMEs), allow a study of correlation lengths of magnetic field parameters for two types of interplanetary (IP) structures: ICMEs and ambient solar wind. Further, they permit the extension of such investigations to the magnetosheath and to a distance along the Sun-Earth line (X) of about 400 RE. Data acquired by three spacecraft are examined: ACE, in orbit around the LI point Geotail, traveling eastward in the near-Earth solar wind (at R ∼ 30 RE) and Wind, nominally in the distant geomagnetic tail (R ∼ -160 RE) but making repeated excursions into the magnetosheath/solar wind due to the flapping of the tail. Analyses are presented in both time and frequency domains. We find significant differences in the cross-correlation/coherence properties of the ambient interplanetary magnetic field (IMF) and ICME parameters. For the ambient IMF, we find high coherence to be confined to low frequencies, consistent with other studies. In contrast, ICME magnetic field parameters remain generally coherent up to much higher frequencies. Scale lengths of ICME magnetic field parameters are in excess of 400 RE. High speeds of ∼ 1700 km s-1 are inferred from the plot of phase difference versus frequency, consistent with that obtained from plasma instruments. To strengthen these results and to extend them to include dependence on the distance perpendicular to the Sun-Earth line (Y), we examine a 28-day interval in year 2001 characterized by a sequence of 10 ICMEs and containing roughly equal ambient solar wind and ICME time intervals. ACE-Wind X and Y separations were ∼220 and ∼250 RE, respectively. We find good coherence/correlation alternating with poor values. In particular, we find that in general ICME coherence/correlation lengths along Y are larger by a factor of 3-5 than those quoted in the literature for ambient solar wind parameters. Our findings are good news for the space weather effort, which depends crucially on predicting the arrival of large events, since they make possible the placement of upstream monitors to give a longer lead time than at L1. Copyright 2005 by the American Geophysical Union.

We study a very fast interplanetary shock (IP shock) event observed on 29 October 2003 based on the Geotail particle and field measurements in the solar wind. During this event the intensity of high-energy solar energetic particles (greater than several to several tens of MeV) was quite high, causing a serious background problem for plasma particle measurements on Geotail as well as. on the other spacecraft. The magnetic/electric field measurements and the plasma wave measurement aboard Geotail, on the other hand, were free from such a background problem and provided a reliable estimate for the local plasma parameters including the plasma density. From these measurements, our best estimation for the local shock velocity is ∼2000 km/s in the observer's rest frame or ∼1400 km/s in the upstream plasma rest frame. The corresponding Alfvén Mach number is ∼12. It is found that the timing analysis of the shock arrivals at ACE and Geotail gives a shock velocity significantly lower than the above value. We argue that this difference is due to the shock surface rippling by 15-20 deg. We also comment that this IP shock had a property of "cosmic-ray-mediated" shock, namely a shock having a spatial structure affected by pressures exerted by nonthermal particles accelerated by the shock itself. Copyright 2005 by the American Geophysical Union.

[1] On 19 October 1995 the Geotail satellite skimmed along the quasi-perpendicular bow shock for more than 3 hours, and field-aligned ion beams (FABs) were continuously observed in the foreshock region. Also observed were 11 crossings with the bow shock where these FABs are thought to be generated. The upstream condition of the bow shock was in the state of low Mach number (MA ∼ 2.9) and low beta (β ∼ 0.02). By a detailed study of the evolution of the ion distribution across one of the crossings, we have found that leakage as origin of these ions from the magnetosheath is unlikely. Comparison of the observations with simulations suggests that FAB ions are generated by multiple interaction of incoming solar wind ions with the bow shock. We have then compared the FAB flux normalized by the solar wind flux, F̄, with the shock angle 0Bn and have found that F̄ falls off rapidly just above 0Bn &gt 60°, but it maintains significant level (F̄ ∼ 0.01%) up to ∼75°. Copyright 2005 by the American Geophysical Union.