浅村 和史

With two electron beam sources, we have tested two new Hamamatsu [Hamamatsu Photonics K.K., Shizuoka, Japan (http://www.hamamatsu.com/)] avalanche photodiodes (APDs) of spl 3988 and spl 6098 to detect electron beams up to 100 keV. Though our previous results showed the effectiveness and the advantage of an APD to measure 2-40 keV electrons, its upper limit was not high enough to detect so-called medium-energy electrons. In addition to the limitation of its detectable range, the response at different energies was also not linear. These newly developed APDs, which have thicker depletion-layers, provide full coverage of this missing range along with a good linearity. The depletion-layer thickness was increased to 140 pm for both APDs. the dead-layer of spl 3988 became 10 times thicker than that of spl 6098. The thin-surface dead-layer and thick depletion-layer of spl 6098 allows the detection of electrons from 3 keV up to 100 keV with a good linearity and with an excellent energy resolution of 4 keV at 100-keV electrons. The wide dynamic range from 3 keV to 100 keV of those APDs will increase their appeal in detecting electrons for space plasma research. (C) 2008 Elsevier B.V. All rights reserved.

We have developed a new energy/mass spectrometer for medium energy range ∼10-200 keV/q) ion measurements in the Earth's magnetosphere and interplanetary space. The wide field-of-view ∼360° fan) enables acquisition of 3-D distribution functions for all the major ions, by utilizing spacecraft spin motions. The g-factor is much larger than the previous ion mass spectrometers in the medium energy range. The mass analysis unit that measures ion time-of-flights is well designed to realize a lightweight and simple signal processing. Laboratory experiments with a test model show that the performance of mass spectroscopy agrees with numerical simulations. Medium energy ion mass spectrometer with this new design will surely be useful for upcoming space missions in the inner magnetosphere, reconnection regions, and other energetic plasma structures/phenomena in space. © 2008 IEEE.

We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude ( magnetic latitude: 62 degrees, L similar to 4.6), using an all-sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm ( H-beta) were often observed at latitudes separated equatorward from the main auroral oval. From a 1-year observation ( 4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre- and post-midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250 - 800 km, respectively. We found that as isolated arcs moved equatorward ( poleward), the frequencies of the simultaneous Pc 1 pulsations increased ( decreased). Using the Tsyganenko-02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron ( EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high-energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low-latitude auroral emissions away from the ordinary auroral oval.

The relationship between bulk ion upflows and suprathermal ions was investigated using data simultaneously obtained from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Reimei satellite. Simultaneous observations were conducted in November 2005 and August 2006, and 14 conjunction data sets have been obtained at approximately 630 km in the dayside ionosphere. Suprathermal ions with energies of a few eV were present in the dayside cusp region, and the ion velocity distribution changed from an isotropic Maxwellian near the cusp region to tail heating at energies above a few eV in the cusp region. The velocity distribution of the suprathermal ions has a peak perpendicular or oblique to the geomagnetic field, and the temperature of the suprathermal ions was 0.9-1.4 eV. An increase in the phase space density (PSD) of the suprathermal ions, measured with the Reimei, was correlated with bulk ion upflow observed at the same altitude using EISCAT, and with the energy flux of precipitating electrons with energies of 50-500 eV. The PSD also has a good correlation with the electron temperature, which was increased by precipitation, but not with the ion temperature (0.1-0.3 eV) at the same altitude measured with EISCAT. These results suggest that plasma waves such as broadband extremely low frequency (BBELF) wavefields associated with precipitation are connected to the bulk ion upflows in the cusp and effectively cause the heating of suprathermal ions. The heating of suprathermal ions disagrees with anisotropic heating due to O+-O resonant charge exchange. Copyright 2008 by the American Geophysical Union.

In December 2006, a single active region produced a series of proton solar flares, with X-ray class up to the X9.0 level, starting on 5 December 2006 at 10:35 UT. A feature of this X9.0 flare is that associated MeV particles were observed at Venus and Mars by Venus Express (VEX) and Mars Express (MEX), which were similar to 80 degrees and similar to 125 degrees east of the flare site, respectively, in addition to the Earth, which was similar to 79 degrees west of the flare site. On December 5, 2006, the plasma instruments ASPERA-3 and ASPERA-4 on board MEX and VEX detected a large enhancement in their respective background count levels. This is a typical signature of solar energetic particle (SEP) events, i.e., intensive MeV particle fluxes. The timings of these enhancements were consistent with the estimated field-aligned travel time of particles associated with the X9.0 flare that followed the Parker spiral to reach Venus and Mars. Coronal mass ejection (CME) signatures that might be related to the proton flare were twice identified at Venus within < 43 and < 67 h after the flare. Although these CMEs did not necessarily originate from the X9.0 flare on December 5, 2006, they most likely originated from the same active region because these characteristics are very similar to flare-associated CMEs observed on the Earth. These observations indicate that CME and flare activities on the invisible side of the Sun may affect terrestrial space weather as a result of traveling more than 90 degrees in both azimuthal directions in the heliosphere. We would also like to emphasize that during the SEP activity, MEX data indicate an approximately one-order of magnitude enhancement in the heavy ion outflow flux from the Martian atmosphere. This is the first observation of the increase of escaping ion flux from Martian atmosphere during an intensive SEP event. This suggests that the solar EUV flux levels significantly affect the atmopheric loss from unmagnetized planets. (c) 2008 Elsevier Ltd. All rights reserved.

The Analyzer of Space Plasma and EneRgetic Atoms (ASPERA-3) on board Mars Express is designed to study the interaction between the solar wind and the atmosphere of Mars and to characterize the plasma and neutral gas environment in near-Mars space. Neutral Particle Detectors (NPD-1 and 2), which form part of the ASPERA-3 instrument suite, are Energetic Neutral Atom (ENA) detectors which use the time-of-flight (ToF) technique to resolve the energy of detected particles. In the present study, we perform a statistical analysis of NPD ToF data collected between 14 March 2004 and 17 June 2004 when Mars Express was located at the dayside of Mars looking toward the planet. After pre-processing and removal of UV contamination, the ToF spectra were fitted with simple analytical functions so as to derive a set of parameters. The behavior of these parameters, as a function of spacecraft position and attitude, is compared with a model, which describes ENA generation by charge exchange between shocked solar wind protons and,extended Martian exosphere. The observations and the model agree well, indicating that the recorded signals are charge-exchanged shocked solar wind. (c) 2008 Elsevier Ltd. All rights reserved.

We have an unique opportunity to compare the magnetospheres of two non-magnetic planets as Mars and Venus with identical instrument sets Aspera-3 and Aspera-4 on board of the Mars Express and Venus Express missions. We have performed both statistical and case studies of properties of the magnetosheath ion flows and the flows of planetary ions behind both planets. We have shown that the general morphology of both magnetotails is generally identical. In both cases the energy of the light (H(+)) and the heavy (O(+), etc.) ions decreases from the tail periphery (several keV) down to few eV in the tail center. At the same time the wake center of both planets is occupied by plasma sheet coincident with the current sheet of the tail. Both plasma sheets are filled by accelerated (500-1000 eV) heavy planetary ions. We report also the discovery of a new feature never observed before in the tails of non-magnetic planets: the plasma sheet is enveloped by consecutive layers of He(+) and H(+) with decreasing energies. (c) 2007 Elsevier Ltd. All rights reserved.

The ASPERA-4 instrument on board the Venus Express spacecraft offers for the first time the possibility to directly measure the emission of energetic neutral atoms (ENAs) in the vicinity of Venus. When the spacecraft is inside the Venus shadow a distinct signal of hydrogen ENAs usually is detected. It is observed as a narrow tailward stream, coming from the dayside exosphere around the Sun direction. The intensity of the signal reaches several 10(5) cm(-1) sr(-1) s(-1), which is consistent with present theories of the plasma and neutral particle distributions around Venus. (c) 2007 Elsevier Ltd. All rights reserved.

We report the detection of electrons due to photo-ionization of atomic oxygen and carbon dioxide in the Venus atmosphere by solar helium 30.4 van photons. The detection was by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) on the Venus Express (VEx) European Space Agency (ESA) mission. Characteristic peaks in energy for such photoelectrons have been predicted by Venus atmosphere/ionosphere models. The ELS energy resolution (Delta E/E similar to 7%) means that these are the first detailed measurements of such electrons. Considerations of ion production and transport in the atmosphere of Venus suggest that the observed photoelectron peaks are due primarily to ionization of atomic oxygen. (c) 2007 Elsevier Ltd. All rights reserved.

Plasma and magnetic field measurements made onboard the Venus Express on June 1, 2006, are analyzed and compared with predictions of a global model. It is shown that in the orbit studied, the plasma and magnetic field observations obtained near the North Pole under solar minimum conditions were qualitatively and, in many cases also, quantitatively in agreement with the general picture obtained using a global numerical quasi-neutral hybrid model of the solar wind interaction (HYB-Venus). In instances where the orbit of Venus Express crossed a boundary referred to as the magnetic pileup boundary (MPB), field line tracing supports the suggestion that the MPB separates the region that is magnetically connected to the fluctuating magnetosheath field from a region that is magnetically connected to the induced magnetotail lobes. (c) 2007 Elsevier Ltd. All rights reserved.

For the first time since 1992 when the Pioneer Venus Orbiter (PVO) ceased to operate, there is again a plasma instrument in orbit around Venus, namely the ASPERA-4 flown on Venus Express (inserted into an elliptical polar orbit about the planet on April 11, 2006). In this paper we report on measurements made by the ion and electron sensors of ASPERA-4 during their first five months of operation and, thereby, determine the locations of both the Venus bow shock (BS) and the ion composition boundary (ICB) under solar minimum conditions. In contrast to previous studies based on PVO data, we employ a 3-parameter fit to achieve a realistic shape for the BS. We use a different technique to fit the ICB because this latter boundary cannot be represented by a conic section. Additionally we investigate the dependence of the location of the BS on solar wind ram pressure (based on ASPERA-4 solar wind data) and solar EUV flux (using a proxy from Earth). (c) 2008 Elsevier Ltd. All rights reserved.

At an altitude of 610-670 km, the Japanese satellite Reimei was the first to discover a new type of ion injections into the topside ionosphere in or in the vicinity of the cusp. These ion injections, called Microburst Cusp Ion Precipitation (MCIP), were spatially embedded into the dominant precipitation of magnetosheath-like particles. They were observed in approximately one third of all cusp traversals, and were characterized by a relatively low energy (with less than a few hundred electron-volts) and relatively short-lived nature (with a typical lifetime of 1 to 2 s). The characteristic energy decreases with time (Type 1), and sometimes does not clearly exhibit energy-time dispersion (Type 3). Only one event exhibits the characteristic energy increasing with time (Type 2). Applying the time-of-flight model (in which higher energy ions arrive at the observation point first) and the velocity filter model (in which the characteristic energy decreases with distance from a source field line under the influence of perpendicular drift motion), we estimated the source distance from Reimei. This paper proposes that a localized electric field, probably associated with inertial Alfven waves and/or ionospheric Alfven resonator, could have been generated at short intervals in time or in isolated regions at an altitude less than 3000 km, which results in MCIPs accompanied with energy-time and energy-pitch angle dispersions observed at an altitude of 610 to 670 km.

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.

We present results from co-ordinated measurements with the low altitude REIMEI satellite and the ESR (EISCAT Svalbard Radar), together with other ground-based instruments carried out in February 2006. The results mainly relate to the dayside cusp where clear signatures of so-called ion-dispersion are seen in the satellite data. The cusp ion-dispersion is important for helping to understand the temporal and spatial structure of magnetopause reconnection. Whenever a satellite crosses boundaries of flux tubes or convection cells, cusp structures such as ion-dispersion will always be encountered. In our case we observed 3 distinct steps in the ion energy, but it includes at least 2 more steps as well, which we interpret as temporal features in relation to pulsed reconnection at the magnetopause. In addition, fast variations of the electron flux and energy occurring during these events have been studied in detail. The variations of the electron population, if interpreted as structures crossed by the REIMEI satellite, would map near the magnetopause to similar features as observed previously with the Cluster satellites. These were explained as Alfven waves originating from an X-line of magnetic reconnection.

Venus, unlike Earth, is an extremely dry planet although both began with similar masses, distances from the Sun, and presumably water inventories. The high deuterium-to-hydrogen ratio in the venusian atmosphere relative to Earth's also indicates that the atmosphere has undergone significantly different evolution over the age of the Solar System(1). Present-day thermal escape is low for all atmospheric species. However, hydrogen can escape by means of collisions with hot atoms from ionospheric photochemistry(2), and although the bulk of O and O-2 are gravitationally bound, heavy ions have been observed to escape(3) through interaction with the solar wind. Nevertheless, their relative rates of escape, spatial distribution, and composition could not be determined from these previous measurements. Here we report Venus Express measurements showing that the dominant escaping ions are O+, He+ and H+. The escaping ions leave Venus through the plasma sheet (a central portion of the plasma wake) and in a boundary layer of the induced magnetosphere. The escape rate ratios are Q(H+)/Q(O+) = 1.9; Q(He+)/Q(O+) = 0.07. The first of these implies that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.

The general scientific objective of the ASPERA-4 (Analyser of Space Plasmas and Energetic Atoms) experiment is to study the solar wind-atmosphere interaction and characterise the plasma and neutral gas environment in the near-Venus space through energetic neutral atom (ENA) imaging and local charged particle measurements. The studies to be performed address the fundamental question: How strongly do the interplanetary plasma and electromagnetic fields affect the Venusian atmosphere? The ASPERA-4 instrument comprises four sensors; two ENA sensors, electron and ion spectrometers. The neutral particle imager (NPI) provides measurements of the integral ENA flux (0.1-60 keV) with no mass and energy resolution but relatively high angular resolution. The neutral particle detector (NPD) provides measurements of the ENA flux, resolving velocity (0.1-10keV) and mass (H and 0) with a coarse angular resolution. The electron spectrometer (ELS) is a standard top-hat electrostatic analyser in a very compact design. These three sensors are located on a scanning platform providing a 4 pi coverage. The instrument also contains an ion mass composition sensor, IMA (ion mass analyser). Mechanically, IMA is a separate unit electrically connected with the ASPERA-4 main unit. IMA provides ion measurements in the energy range 0.01-36keV/q for the main ion components H(+), He(++), He(+), and the ion group with M/q 20-80amu/q. (C) 2007 Elsevier Ltd. All rights reserved.

Low-energy neutral atom (LENA) observations bring us important information on particle environments around celestial objects such as Mercury and the Moon. In this paper, we report on new development of an LENA instrument for planetary explorations. The instrument is light weight (2 kg), and capable of mass and energy discrimination with a large sensitivity. The performance of the instrument is investigated by numerical simulations. By using our new computer code, we calculated 3D particle trajectories including ionization, neutralization, surface scattering, and secondary electron creation. This enables us to obtain detailed performance characterization of LENA measurements. We also made trajectory tracing of photons entering the instrument to acquire photon rejection capability. This LENA instrument has been selected for both the Indian lunar exploration mission Chandrayaan-1 and European-Japanese Mercury exploration mission BepiColombo. (C) 2007 Elsevier Ltd. All rights reserved.

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.(c) 2007 American Institute of Physics.

This paper describes the on-orbit results and lessons-learned of the small scientific satellite "INDEX" (REIMEI) for aurora observation and demonstration of advanced satellite technologies. INDEX is a small satellite with 72kg mass, and is provided with three-axis attitude controll capabilities for aurora observation. INDEX was launched into a nearly sun synchronous polar orbit on Aug. 23rd, 2005 (UT) from Baikonur, Kazakhstan by Dnepr rocket. INDEX satellite has been satisfactorily working on the orbit for 24 months at present of August,2007. Three axis control is achieved with accuracy of 0.1 deg(3 σ). Multi-spectrum images of aurora are taken with 8Hz rate and 2 km spatial resolution to investigate the aurora physics. INDEX is performing the simultaneous observation of aurora images and particle measurements. INDEX indicates that even a small satellite launched as a piggy-back can successfully perform unique scientific mission purposes. Copyright IAF/IAA. All rights reserved.

© 2016 World Scientific Publishing Co Pte Ltd. 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 developed a new electrostatic analyzer which enables medium energy (less than or similar to 200 keV/q) plasma particle measurements with full solid angle coverage. The design of the test model realizes the uppermost measurement energy of similar to 200 keV/q 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. (c) 2006 American Institute of Physics.

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 mu 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 8keV, 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 mu 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. (c) 2006 Elsevier B.V. All rights reserved.

Using data of the ASPERA-3 instrument on board the European Mars Express spacecraft we investigate the effect of the martian crustal fields on electrons intruding from the magnetosheath. For the crustal field strength we use published data obtained by the Mars Global Surveyor MAG/ER instrument for a fixed altitude of 400 km. We use statistics on 13 months of 80-100 eV electron observations to show that the electron intrusion altitude determined by a probability measure is approximately linearly dependent on the total field strength at 400 km altitude. We show that on the dayside the mean electron intrusion altitude describes the location of the Magnetic Pile-Up Boundary (MPB) such that we can quantify the effect of the crustal fields on the MPB. On the nightside we quantify the shielding of precipitating electrons by the crustal fields. (c) 2005 Elsevier Inc. All rights reserved.

The Electron Spectrometer (ELS) instrument of the ASPERA-3 package on the Mars Express satellite has recorded photoelectron energy spectra up to apoapsis (similar to 10.000 km altitude). The characteristic photoelectron shape of the spectrum is sometimes seen well above the ionosphere in the evening sector across a wide range of near-equatorial latitudes. Two numerical models are used to analyze the characteristics of these high-altitude photoelectrons. The first is a global, multi-species MHD code that produces a 3-D representation of the magnetic field and bulk plasma parameters around Mars. It is used here to examine the possibility of magnetic connectivity between the high-altitude flanks of the martian ionosheath and the subsolar ionosphere. It is shown that some field lines in this region are draped interplanetary magnetic lines while others are open field lines (connected to both the IMF and the crustal magnetic field sources). The second model is a kinetic electron transport model that calculates the electron velocity space distribution along a selected, non-uniform, magnetic field line. It is used here to simulate the high-altitude ELS measurements. It is shown that the photoelectrons are essentially confined to the source cone, as governed by magnetic field inhomogeneity along the field line. Reasonable agreement is shown between the data and the model results, and a method is demonstrated for inferring properties of the local and photoelectron source region magnetic field from the ELS measurements. Specifically, the number of sectors in which photoelectrons are measured is a function of the magnetic field intensity ratio and the field's angle with respect to the detector plane. In addition, the sector of the photoelectron flux peak is a function of the magnetic field azimuthal angle in the detector plane. (c) 2005 Elsevier Inc. All rights reserved.

Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite on Mars Express have been analyzed to determine the mass composition of the escaping ion species at Mars. We have examined 77 different ion-beam events and we present the results in terms of flux ratios between the following ion species: CO(2)(+)/O(+) and O(2)(+)/O(+). The following ratios averaged over all events and energies were identified: CO(2)(+)/O(+) = 0.2 and O(2)(+)/O(+) = 0.9. The values measured are significantly higher, by a factor of 10 for O(2)(+)/O(+), than a contemporary modeled ratio for the maximum fluxes which the martian ionosphere can supply. The most abundant ion species was found to be O(+), followed by O(2)(+) and CO(2)(+). We estimate the loss of CO(2)(+) to be 4.0 x 10(24) s(-1) (0.29 kg s(-1)) by using the previous measurements of Phobos-2 in our calculations. The dependence of the ion ratios in relation to their energy ranges we studied, 0.3-3.0 keV, indicated that no clear correlation was found. (c) 2005 Elsevier Inc. All rights reserved.

The ELectron Spectrometer (ELS) from the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) flown on the Mars Express spacecraft has an No energy resolution. combined with the capability to oversample the martian electron distribution. This makes possible the resolution and identification of electrons generated as a result of the He 304 angstrom ionization of CO(2) at the martian exobase on the dayside of the planet. Ionospheric photoelectrons were observed during, almost every pass into the ionosphere and CO(2) photoelectron peaks were identified near the terminator. Atmospherically generated CO(2) photoelectrons are also observed at 10,000 km altitude in the martian tail near the inner magnetospheric boundary. Observations over a wide range of spacecraft orbits showed a consistent presence of photoelectrons at locations along the inner magnetospheric boundary and in the ionosphere, front an altitude of 250 to 10,000 km. (c) 2006 Elsevier Inc. All rights reserved.

The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on-board the Mars Express spacecraft (MEX) measured penetrating solar wind plasma and escaping/accelerated ionospheric plasma at very low altitudes (250 km) in the dayside subsolar region. This implies a direct exposure of the martian topside atmosphere to solar wind plasma forcing leading to energization of ionospheric plasma. The ion and electron energization and the ion outflow from Mars is surprisingly similar to that over the magnetized Earth. Narrow "monoenergetic" cold ion beams, ion beams with broad energy distributions, sharply peaked electron energy spectra, and bidirectional streaming electrons are particle features also observed near Mars. Energized martian ionospheric ions (O(+), O(2)(+), CO(2)(+), etc.) flow in essentially the same direction as the external sheath flow. This suggests 2 2 that the planetary ion energization couples directly to processes in the magnetosheath/solar wind. On the other hand, the beam-like distribution of the energized plasma implies more indirect energization processes like those near the Earth, i.e., energization in a magnetized environment by waves and/or parallel (to B) electric fields. The general conditions for martian plasma energization are, however, different from those in the Earth's magnetosphere. Mars has a weak intrinsic magnetic field and solar wind plasma may therefore penetrate deep into the dense ionospheric plasma. Local crustal magnetization, discovered by Acuna et al. [Acuna, M.J., Connerey, J., Ness, N., Lin, R., Mitchell, D., Carlsson, C., McFadden, J., Anderson, K., Reme, H., Mazelle, C., Vignes, D., Wasilewski, P., Cloutier, P., 1999. Science 284, 790-793], provide some dayside shielding against the solar wind. On the other hand, multiple magnetic anomalies may also lead to "hot spots" facilitating ionospheric plasma energization. We discuss the ASPERA-3 findings of martian ionospheric ion energization and present evidences for two types of plasma energization processes responsible for the low- and mid-altitude plasma energization near Mars: magnetic field-aligned acceleration by parallel electric fields and plasma energization by low frequency waves. (c) 2005 Elsevier Inc. All rights reserved.

The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment flown on the Mars Express (MEX) spacecraft includes the Electron Spectrometer (ELS) as part of its complement. The ELS instrument measures the differential electron flux spectrum in a 128-level logarithmic energy sweep within a time period of 4 s. The orbital path of MEX traverses the martian sheath, cusps, and tail where ELS recorded periodic electron intensity oscillations. These oscillations comprised periodic variations of up to an order of magnitude (peak to valley) in energy flux, with the largest amplitudes in the tens to hundreds of eV range. The observed oscillations displayed periods ranging from minutes down to the instrument sweep resolution of 4 s. In the cases analyzed here, the frequency of the integrated electron energy flux typically peaked between 0.01 and 0.02 Hz. This frequency range is nearly the same as the typical O(+) gyrofrequency in the magnetosheath, calculated using magnetometer data from Mars Global Surveyor. Due to the motion of the spacecraft, it is unclear if the wave structures observed were permanent standing waves or rather constituted waves propagating past the spacecraft. (c) 2005 Elsevier Inc. All fights reserved.

We present the first results from the ion mass analyzer IMA of the ASPERA-3 instrument on-board of Mars Express. More than 200 orbits for May 2004-September 2004 time interval have been selected for the statistical study of the distribution of the atmospheric origin ions in the planetary wake. This Study shows that the martian magnetotail consists of two different ion regimes. Planetary origin ions of the first regime form the layer adjacent to the magnetic pile-up boundary. These ions are accelerated to energy greater than 2000 eV and exhibit a gradual decreasing of energy down to the planetary tail. The second plasma regime is observed in the planetary shadow. The heavy ions (considered as planetary ones) are accelerated to the energy of the solar wind protons. Obviously the acceleration mechanism is different for the different plasma regimes. Study of two plasma regimes in the frame referred to the interplanetary magnetic field (IMF) direction (we used MGS magnetometer data to obtain the IMF clock angle) clearly shows their spatial anisotropy. The monoenergetic plasma in the planetary shadow is observed only in the narrow angular sector around the positive direction of the interplanetary electric field. (c) 2005 Elsevier Inc. All rights reserved.

We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal front the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA Simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs front upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future. (c) 2006 Elsevier Inc. All rights reserved.

Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic 'anomaly' regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere. (c) 2005 Elsevier Inc. All rights reserved.

We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction. (c) 2005 Elsevier Inc. All rights reserved.

Observations made by the ASPERA-3 experiment onboard the Mars Express spacecraft found within the martian magnetosphere beams of planetary ions. In the energy (E/q)-time spectrograms these beams are often displayed as dispersive-like, ascending or descending (whether the spacecraft moves away or approach the planet) structures. A linear dependence between energy gained by the beam ions and the altitude from the planet suggests their acceleration in the electric field. The values of the electric field evaluated from ion energization occur close to the typical values of the interplanetary motional electric field. This suggests an effective penetration of the solar wind electric field deep into the martian magnetosphere or generation of large fields within the magnetosphere. Two different classes of events are found. At the nominal solar wind conditions, a penetration I occurs near the terminator. At the extreme solar wind conditions, the boundary of the induced magnetosphere moves to a more dense upper atmosphere that leads to a strong scavenging of planetary ions from the dayside regions. (c) 2005 Elsevier Inc. All rights reserved.

The ASPERA-3 experiment onboard the Mars Express spacecraft revealed, near the wake boundary of Mars, a spatially narrow, strip-like plasma structure composed of magnetosheath-like electrons and planetary ions. The peak electron energy often exceeds the peak energy at the bow shock that indicates a significant heating (acceleration) during the structure formation. It is shown that this structure is formed during efficient plasma penetration into the martian magnetosphere in the region near the terminator. The penetration of sheath electrons and their gradual heating (acceleration) is accompanied by a change of the ion composition from a solar wind plasma to a planetary plasma dominated by oxygen ions. A possible mechanism of plasma inflow to the magnetosphere is discussed. (c) 2005 Elsevier Inc. All rights reserved.

The Neutral Particle Detector (NPD), an Energetic Neutral Atom (ENA) sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) on board Mars Express, detected intense fluxes of ENAs emitted from the subsolar region of Mars. The typical ENA fluxes are (4-7) x 10(5) cm(-2) sr(-1) s(-1) in the energy range 0.3-3 keV. These ENAs are likely to be generated in the subsolar region of the martian exosphere. As the satellite moved away from Mars, the ENA flux decreased while the field of view of the NPD pointed toward the subsolar region. These decreases occurred very quickly with a time scale of a few tens of seconds in two thirds of the orbits. Such a behavior can be explained by the spacecraft crossing a spatially constrained ENA jet, i.e., a highly directional ENA emission from a compact region of the subsolar exosphere. This ENA jet is highly possible to be emitted conically from the subsolar region. Such directional ENAs can result from the anisotropic solar wind flow around the subsolar region. but this can not be explained in the frame of MHD models. (c) 2005 Elsevier Inc. All rights reserved.

The neutral particle detector (NPD) on board Mars Express has observed energetic neutral atoms (ENAs) from a broad region on the dayside of the martian upper atmosphere. We show one such example for which the observation was conducted at an altitude of 570 km, just above the induced magnetosphere boundary (IMB). The time of flight spectra of these ENAs show that they had energies of 0.2-2 keV/amu, with an average energy of similar to 1.1 keV/amu. Both the spatial distribution and the energy of these ENAs are consistent with the backscattered ENAs, produced by an ENA albedo process. This is the first observation of backscattered ENAs from the martian upper atmosphere. The origin of these ENAs is considered to be the solar wind ENAs that are scattered back by collision processes in the martian upper atmosphere. The particle flux and energy flux of the backscattered ENAs are 0.9-1.3 x 10(7) cm(-2) s(-1) and similar to 9.5 x 10(9) eV cm(-2) s(-1), respectively. (c) 2005 Elsevier Inc. All rights reserved.

We have studied the interaction of fast solar wind hydrogen atoms with the martian atmosphere by a three-dimensional Monte Carlo simulation. These energetic neutral hydrogen atoms, H-ENAs, are formed upstream of the martian bow shock. Both H-ENAs scattered and non-scattered from the martian atmosphere/exosphere were studied. The colliding H-ENAs were found to scatter both to the dayside and nightside. On the dayside they contribute to the so-called H-ENA albedo. On the nightside the heated and scattered hydrogen atoms were found also in the martian wake. The density, the energy distribution function and the direction of the velocity of H-ENAs on the nightside are presented. The present study describes a novel '' ENA sounding '' technique in which energetic neutral atoms are used to derive information of the properties of planetary exosphere and atmosphere in a similar manner as the solar wind photons are used to derive atmospheric densities by measuring the scattered UV light. A detailed study of the direction and energy of the scattered and non-scattered H-ENAs suggest that the ENA sounding is a method to study the interaction between the planetary atmosphere and the solar wind and to monitor the density, and likely also the magnetization, of the planetary upper atmosphere. Already present-day ENA instrument should be capable to detect the analyzed particle fluxes. (c) 2006 Elsevier Inc. All rights reserved.

Measurements of energetic neutral atoms (ENA) generated in the magnetosheath at Mars are reported. These ENAs are the result of charge exchange collisions between solar wind protons and neutral oxygen and hydrogen in the exosphere of Mars. The peak of the observed ENA flux is 1.3 x 10(11) m(-2) sr(-1) s(-1). For the case studied here, i.e., the passage of Mars Express through the martian magnetosheath around 20: 15 UT on 3 May 2004. the measurements agree with an analytical model of the ENA production at the planet. It is possible to find parameter values in the model such that the observed peak in the ENA count rate during the spacecraft passage through the magnetosheath is reproduced. (c) 2005 Elsevier Inc. All rights reserved.

Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-attitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space.

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. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

Low-energy neutral atom (LENA) imaging is an important technique for doing planetary sciences at magnetized and unmagnetized planets. In the case of the Moon, the precipitating solar-wind causes sputtering, which releases surface atoms as LENAs into space. Moreover, the solar-wind ions may be back-scattered from the surface into space as neutral atoms. At Mercury, in addition to the above processes, LENAs are also generated by the charge-exchange of energetic ions with the exospheric gasses. Global LENA mass spectroscopic imagery at the Moon and at Mercury provides us information on their surfaces and the interaction processes between energetic particles and the surfaces via remote-sensing using LENAs. We are developing a state-of-the-art LENA instrument for the Indian lunar exploration mission Chandrayaan-1 and the Mercury exploration mission BepiColombo. The instrument is light-weight and capable of mass discrimination, including heavy components such as iron, and has high sensitivity to fulfill various scientific objectives in the area of planetary sciences. (C) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

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 Andoya 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.

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. (C) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper reports on the Sub-keV Atom Reflecting Analyzer (SARA) experiment that will be flown on the first Indian lunar mission Chandrayaan-1. The SARA is a low energy neutral atom (LENA) imaging mass spectrometer, which will perform remote sensing of the lunar surface via detection of neutral atoms in the. energy range from 10 eV to 3 keV from a 100 kin polar orbit. In this report we present the basic design of the SARA experiment and discuss various scientific issues that will be addressed. The SARA. instrument consists of three major subsystems: a LENA sensor (CENA), a solar wind monitor (SWIM), and a digital processing unit (DPU). SARA will be used to image the solar wind-surface interaction to study primarily the surface composition and surface magnetic anomalies and associated mini-magnetospheres. Studies of lunar exosphere sources and space weathering on the Moon will also be attempted. SARA is the first LENA imaging mass spectrometer of its kind to be flown on a space mission. A replica of SARA is planned to fly to Mercury onboard the BepiColombo mission.

[1] The SS-520-2 sounding rocket skimmed over the high-latitude part of the cusp region and observed fine-scale field-aligned electron precipitations in the vicinity of the inverted-V structures with the Low Energy Particle-Electron Spectrum Analyzer (LEP-ESA). There are at least two types of fine-scale electron precipitations, namely "edge-type electron bursts'' and "multiple energy-time dispersions.'' Edge-type electron bursts were observed only at the edge of the inverted-V region, whereas multiple energy-time dispersions were observed separately from the inverted-V region as well as within or overlapping it. The latter was characterized by field-aligned precipitations with falling energies from similar to 200 eV down to similar to 20 eV at a repetition rate of 1 - 2 Hz. Source altitudes were estimated using the energy-time and pitch angle-time dispersions. As a result, we found that the source altitudes were distributed along the geomagnetic field at altitudes of several thousand kilometers, depending on the accelerated energies of electrons. Higher-energy electrons are generated at higher altitudes. The source temperature of the energy-time dispersion was much higher than that of ionospheric cold electrons. We suggest that electrons injected from the magnetosheath were accelerated by inertial Alfven waves at altitudes of several thousands of kilometers.

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.

We have constructed a one-dimensional numerical model of electron acceleration with dispersive Alfven waves using realistic parameters based on a rocket observation in the high-latitude part of the cusp region. This paper demonstrates that our model could quantitatively reproduce important characteristics of observed electron energy-time dispersions, such as their fluxes, energy range, pitch angle distribution, and source altitudes. The energy-time dispersion at the rocket altitude is produced by a time-of-flight effect of magnetosheath-originated electrons accelerated by the resonant interaction with inertial Alfven waves (IAWs) at altitudes of 2000 similar to 6000 km. The higher-energy electrons are generated at higher altitudes. The energy-time dispersion changes according to three key parameters: wave power, perpendicular wavelength, and wave frequency. The wave power affects the flux and the maximum electron energy, and the perpendicular wavelength affects the source altitude calculated by the time-of-flight analysis, while the wave frequency (time period) affects the time width of the energy-time dispersion. We summarize a reasonable set of these parameters for a typical energy-time dispersion observed in the cusp/cleft region. Finally, we suggest that the IAWs are generated at the dayside magnetopause in association with magnetic reconnection and then propagate toward the ionosphere along the open field line connected to the magnetosheath. Their resonant acceleration of local electrons injected from the magnetosheath at altitudes of several thousand kilometers is the cause for multiple electron energy-time dispersions observed in the high-latitude part of the cusp region.

We have constructed a one-dimensional numerical model of electron acceleration with dispersive Alfvén waves using realistic parameters based on a rocket observation in the high-latitude part of the cusp region. This paper demonstrates that our model could quantitatively reproduce important characteristics of observed electron energy-time dispersions, such as their fluxes, energy range, pitch angle distribution, and source altitudes. The energy-time dispersion at the rocket altitude is produced by a time-of-flight effect of magrietosheath-originated electrons accelerated by the resonant interaction with inertial Alfvén waves (lAWs) at altitudes of 2000 ̃ 6000 km. The higher-energy electrons are generated at higher altitudes. The energy-time dispersion changes according to three key parameters: wave power, perpendicular wavelength, and wave frequency. The wave power affects the flux and the maximum electron energy, and the perpendicular wavelength affects the source altitude calculated by the time-of-flight analysis, while the wave frequency (time period) affects the time width of the energy-time dispersion. We summarize a reasonable set of these parameters for a typical energy-time dispersion observed in the cusp/cleft region. Finally, we suggest that the lAWs are generated at the dayside magnetopause in association with magnetic reconnection and then propagate toward the ionosphere along the open field line connected to the magnetosheath. Their resonant acceleration of local electrons injected from the magnetosheath at altitudes of several thousand kilometers is the cause for multiple electron energy-time dispersions observed in the high-latitude part of the cusp region. Copyright 2005 by the American Geophysical Union.

[1] The SS-520-2 sounding rocket skimmed over the high-latitude part of the cusp region and observed fine-scale field-aligned electron precipitations in the vicinity of the inverted-V structures with the Low Energy Particle-Electron Spectrum Analyzer (LEP-ESA). There are at least two types of fine-scale electron precipitations, namely "edge-type electron bursts" and "multiple energy-time dispersions." Edge-type electron bursts were observed only at the edge of the inverted-V region, whereas multiple energy-time dispersions were observed separately from the inverted-V region as well as within or overlapping it. The latter was characterized by field-aligned precipitations with falling energies from ∼200 eV down to ∼20 eV at a repetition rate of 1-2 Hz. Source altitudes were estimated using the energy-time and pitch angle-time dispersions. As a result, we found that the source altitudes were distributed along the geomagnetic field at altitudes of several thousand kilometers, depending on the accelerated energies of electrons. Higher-energy electrons are generated at higher altitudes. The source temperature of the energy-time dispersion was much higher than that of ionospheric cold electrons. We suggest that electrons injected from the magnetosheath were accelerated by inertial Alfvén waves at altitudes of several thousands of kilometers. Copyright 2005 by the American Geophysical Union.