阿部 琢美

We present the in-situ measurement of the electron density and its perturbation on the sounding rocket in the ionospheric cusp region during the ICI-2 (Investigation of Cusp Irregularities-2) campaign conducted in Svalbard, Norway in late 2008. The scientific objective of ICI-2 was to investigate generation mechanism(s) of coherent HF radar backscatter targets. Strong coherent HF backscatter echoes are a well-known characteristic of the polar cusp, and are thought to result from field-aligned plasma irregularities with decameter scale length. In this paper, a result from Fixed-Bias Probe (FBP) which aimed at measuring fine-scale (similar to 1 m) electron density perturbation is mainly described.

We present the in-situ measurement of the electron density and its perturbation on the sounding rocket in the ionospheric cusp region during the ICI-2 (Investigation of Cusp Irregularities-2) campaign conducted in Svalbard, Norway in late 2008. The scientific objective of ICI-2 was to investigate generation mechanism(s) of coherent HF radar backscatter targets. Strong coherent HF backscatter echoes are a well-known characteristic of the polar cusp, and are thought to result from field-aligned plasma irregularities with decameter scale length. In this paper, a result from Fixed-Bias Probe (FBP) which aimed at measuring fine-scale (similar to 1 m) electron density perturbation is mainly described.

To study the spatial structure of midlatitude sporadic E (Es) layers, the ultraviolet resonant scattering by magnesium ions (Mg+) in an Es layer was observed during the evening twilight with the Magnesium Ion Imager (MII) on the sounding rocket launched from the Uchinoura Space Center in Kagoshima, Japan. The in situ electron density measured by an onboard impedance probe showed that the Es layer was located at an altitude of 100 km during both the ascent and descent of the flight. Simultaneous observation with a ground-based ionosonde at Yamagawa identified the signature of horizontally "patchy" structures in the Es layer. The MII successfully scanned the horizontal Mg+ density perturbations in the Es layer and found that they had patchy and frontal structures. The horizontal scale and alignment of the observed frontal structure is generally consistent with a proposed theory. To our knowledge, this is the first observation of the two-dimensional horizontal structure of Mg + in an Es layer. Copyright 2010 by the American Geophysical Union.

Velocity distributions of upflowing ions in the polar ionosphere are crucial to understand their destinations. Natural plasma wave observations by the plasma wave and sounder experiments and thermal ion observations by the suprathermal ion mass spectrometer onboard the Akebono satellite at ∼9000 km altitude in the polar magnetosphere during the geomagnetic storms showed that ions in the region of enhanced electron density in the polar cap were dominated by very-low-energy O+ ions (∼85%) with upward velocities of 4-10 km s-1, corresponding to streaming energies of 1.3-8.4 eV. The fluxes of very-low-energy upflowing O+ ions exceeded 1 × 10 9 cm-2 s-1 (mapped to 1000 km altitude) across wide regions. These signatures are consistent with high-density plasma supplied by the cleft ion fountain mechanism. Trajectory calculations of O+ ions based on the Akebono observations as the initial condition showed the transport paths and accelerations of the O+ ions and indicated that the velocities of the very-low-energy upflowing O+ ions through the dayside polar cap are enough to reach the magnetosphere under strong convection. The calculations suggest the importance of the very-low-energy upflowing O + ions with large fluxes in the total O+ ion supply toward the magnetosphere, especially the near-Earth tail region and inner magnetosphere. The initially very-low-energy O+ ions can contribute significantly to the ring current formation during geomagnetic storms since some of the O+ ions were transported into the ring current region with typical energies of ring current ions (several tens of keV) in the trajectory calculations. Copyright 2010 by the American Geophysical Union.

科学気球や観測ロケットなどが飛翔する超高層大気環境における気圧の計測は,技術的にも科学的にも極めて重要である.本研究で開発した飛翔体搭載用小型気圧計は,水晶振動子の共振インピーダンスが圧力に応じて変化する原理を利用した水晶摩擦気圧計と呼ばれるもので,地表から高度100km 付近までに相当する広い計測圧力範囲(10^5〜10^<-2>Pa)に特徴がある.また,センサ部は約100g,データ処理部は約200g と小型軽量であることに加えて1W 以下の低消費電力を達成し,特に重量が厳しく制限される高高度気球などの飛翔体への搭載に適している.腕時計などにも広く使用されている音叉型水晶振動子は耐振動・衝撃性に優れた構造を持ち,高い耐環境性能が要求される観測ロケットにも搭載可能である.本報告では,開発した水晶摩擦気圧計の性能試験結果について述べるとともに,BU30-5 号機を用いた性能実証試験についても報告する.

The on-board small vacuum gauge developed in this study is the quartz friction gauge, which is based on the principle that the resonance impedance of a quartz oscillator varies with the pressure of ambient gas. The gauge has a wide measuring range (10⁵-10^-2 Pa), which corresponds to the atmospheric pressure from the ground to an altitude of about 100 km. The sensor part and data processing part weigh 136 g and 210 g, respectively. In addition, the gauge can operate at a power consumption level of less than 1W. The gauge is suited for high altitude balloon experiments where the weight of on-board instruments must be kept to a minimum. The tuning-fork-shaped quartz oscillator in the gauge is widely used for wrist watches and has high resistance to vibration and shock, and thus the gauge is applicable to sounding rocket experiments that require on-board instruments with high resistance to the environment.

Sounding rocket experiments have been successively conducted for more than 40 years in Japan. These include various scientific and engineering topics. In this paper, we present recent activities of Japanese sounding rocket experiments for the last two years (2007-2008 fiscal year) and also describe a future direction on the experiment in the mid-term range.

In the fiscal year of 2005 and 2006, Japan Aerospace Exploration Agency (JAXA) had successfully launched 10 space vehicles, which included five application satellites, three scientific observation satellites and two sounding rockets with a single stage solid motor. The Institute of Space and Astronautical Science (ISAS) has been continuously conducting space science programs using sounding rockets, scientific satellites and stratospheric balloons. This paper briefly introduces and summarizes the ISAS space activities in the two years.

A fully reusable rocket vehicle is proposed as a sounding rocket for observations of atmospheric phenomena, micro-gravity experiments and so on. Vehicle systems and ground / flight operations are designed for such science observations. For the development of the reusable rocket, a small test vehicle was built and flight-tested. This Reusable Vehicle Testing (RVT) lessons campaign provide repeated experiences of turnaround operations and vertical take-off and landing flights. In the present design of the reusable sounding rocket, the total length and maximum diameter of the vehicle is about 10m and 3m, respectively. The vehicle is propelled by the propulsion system composed of four liquid hydrogen / liquid oxygen engines. The weight of a payload carried to 120 km altitude is 100kg in the nose-fairing. The instrument for observations can be reused because of the repeated flight. The turnaround time for one flight is less than 24 hours (1 day). In the typical ballistic flight up to 120 km, the flight environments under 10(-5)G acceleration is able to be made for about 120 sec. The flight Mach number can be subsonic around the summit in the trajectory. These properties of reusable sounding rocket are expected to be useful and effective for many science missions.

Processes of energy cascade from suprathermal to thermal electrons significantly affect the thermal structure of the lower ionosphere. The Suprathermal Plasma Analyzer (SPA) was developed to measure an energy distribution of thermal and suprathermal electrons (&lt; 5 eV). The principle of this analyzer is based on the innovative combination of a second harmonic method and a channel electron multiplier. Outstanding point of this analyzer are: 1) accurate calibration of electron energy within the order of 0.01 eV, and 2) the energy resolution smaller than 0.15 eV. The SPA was installed in the sounding rocket S-310-37 and observed the electron energy distribution function at the height from 100 km to 140 km.

The sounding rocket measurements in the mid-latitude ionosphere suggest that the electron temperature occasionally increases at 100-110 km altitudes during daytime in winter. Detailed study indicates that such a temperature increase is closely related to the existence of the Sq current focus, because the temperature increase becomes significant when the measurement is made near the center of the Sq focus. In order to elucidate a mechanism to cause the electron temperature increase, the sounding rocket experiment was conducted in Uchinoura Space Center in Japan on January 16, 2007. The rocket was launched at 11:20 JST after identifying that the Sq current was approaching to the planned rocket trajectory. The rocket certainly observed the local increase of the electron temperature at the altitude of 97-101 kin. We present a preliminary analysis of the data such as the electron temperature, density, and its perturbation obtained during this campaign.

The Waves in Airglow Campaign in 2004 (WAVE2004), which aimed to elucidate the formation process of waves in airglow structures from both dynamical and chemical perspectives, was conducted using rocket-borne and ground-based instruments in Japan on 17 January 2004. In this experiment, we observed a large-scale atmospheric gravity wave (AGW), which appeared in both the vertical profiles of sodium density obtained by a Na lidar and the horizontal distributions of airglow emission obtained by an all-sky imager (ASI). Vertical propagation of the AGW accompanied by a shortening of its vertical wavelength was clearly visualized using the Na lidar data. The horizontal wavelength, horizontal phase velocity, period, and propagation direction of the AGW were estimated from the ASI data as 673-774 km, 107-122 m/s, ∼1.75 hours, and north-northeastward, respectively. Using these parameters and the MF radar wind, vertical wavelengths of the wave were calculated from the dispersion relation of gravity waves. The calculated vertical wavelengths were comparable at altitudes of 85.5 km and 93.25 km to those estimated from the variation of the sodium density. Using a simple ray tracing technique, the AGW was traced back to the southern edge of the distorted jet stream near tropopause. This result strongly suggests that an unstable baroclinic wave associated with ageostrophic motions in the jet stream was the wave source of the large-scale AGW observed in the WAVE2004. Copyright 2006 by the American Geophysical Union.

The purpose of this paper is to clarify how the average structure of the Venus nightside ionopause for solar zenith angles (SZA) greater than 90° depends on (1) the direction and (2) the magnitude of the motional electric field of the solar wind. Plasma density structure in the Venus nightside ionosphere has been investigated by using data sets of the Pioneer Venus Orbiter observations. It is found that the distribution of the nightside ionopause locations is asymmetric with respect to the direction of the solar wind electric field, leaning opposite to the electric field vector. It is also found that the asymmetry is increasingly prominent as the magnitude of the motional electric field increases, while not so prominent for small field magnitude. This result suggests that the asymmetric ionopause location in the nightside is related to the acceleration of pickup ions. Copyright 2006 by the American Geophysical Union.

The sounding rocket for the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign was successfully launched from Andoya at 00:33 UT on Dec 13, 2004. Though it was cloudy at the time of launch, the Weber Na lidar was operating intermittently between 20:00 UT and 23:30 UT on Dec 12, observing Na density, temperature and meridional wind between 80 and 100 km. Throughout the lidar observations, we observed significant small (λz <5 km) and medium-scale (λz≈8-15 km) wave activity producing significant wind and temperature shears. There were unusually large (up to 10 m/s and 10 K amplitudes) perturbations of the vertical wind and temperature profiles at 21 UT with a 3 km vertical wavelength that was much stronger in the vertical beam than in the north beam. The atmosphere appeared to become more active as the launch time approached. During the last interval with data, at ∼23:20 UT, Dec. 12th, the lidar profiles revealed a gravity wave in both beams with a magnitude of 5-10 K in temperature and approximately 5 km vertical wavelength. The large background shear plus the wave perturbation produced regions with potential convective instability at multiple altitudes. 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.

Japanese sounding rocket "S-310-35" was launched from Andoya Rocket Range in Norway on December 13, 2004 during Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, in which the rocket-borne in-situ measurements and ground-based measurements were coordinated to conduct a comprehensive observation of the upper atmospheric response against the auroral energy input. The Fast Langmuir Probe (FLP) was installed on the sounding rocket to study thermal structure and energy balance of the plasma by measuring the electron temperature in the polar lower ionosphere. The FLP observations indicate that the electron temperatures were found to be remarkably high in an altitude range from 106 km to 114 km during the ascending phase of the rocket. The lowest part of this high temperature region might be affected by artificial electron beam which was generated by the N-2 temperature instrument on the same rocket. On the other hand, a small increase of the electron temperature was observed at the altitude from 114 to 119 km in the descending phase. This is possibly the first time that both the temperature increase and density fluctuation that may be caused by the Farley-Buneman instability were detected by in-situ observation.

The Japan Aerospace Exploration Agency (JAXA) DELTA rocket experiment, successfully launched from Andoya at 0033 UT on December 13, 2004, supported by ground based optical instruments, primarily 2 Fabry-Perot Interferometers (FPIs) located at Skibotn, Norway (69.3 degrees N, 20.4 degrees E) and the KEOPS Site, Esrange, Kiruna, Sweden (67.8 degrees N, 20.4 degrees E). Both these instruments sampled the 557.7 nm lower thermosphere atomic oxygen emission and provided neutral temperatures and line-of-sight wind velocities, with deduced vector wind patterns over each site. All sky cameras allow contextual auroral information to be acquired. The proximity of the sites provided overlapping fields of view, adjacent to the trajectory of the DELTA rocket. This allowed independent verification of the absolute temperatures in the relatively quiet conditions early in the night, especially important given the context provided by co-located EISCAT ion temperature measurements which allow investigation of the likely emission altitude of the passive FPI measurements. The results demonstrate that this altitude changes from 120 km pre-midnight to 115 km post-midnight. Within this large scale context the results from the FPIs also demonstrate smaller scale structure in neutral temperatures, winds and intensities consistent with localised heating. These results present a challenge to the representation of thermospheric variability for the existing models of the region.

The rotational temperature and number density of molecular nitrogen (N(2)) in the lower thermosphere were measured by the N2 temperature instrument onboard the S-310-35 sounding rocket, which was launched from Andoya at 0:33 UT on 13 December 2004, during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign. The rotational temperature measured at altitudes between 95 and 140 km, which is expected to be equal to neutral temperature, is much higher than neutral temperature from the Mass Spectrometer Incoherent Scatter (MSIS) model. Neutral temperatures in the lower thermosphere were observed using the auroral green line at 557.7 nm by two Fabry-Perot Interferometers (FPIs) at Skibotn and the Kiruna Esrange Optical Platform System site. The neutral temperatures derived from the look directions closest to the rocket correspond to the rotational temperature measured at an altitude of 120 km. In addition, a combination of the all-sky camera images at 557.7 nm observed at two stations, Kilpisjarvi and Muonio, suggests that the effective altitude of the auroral arcs at the time of the launch is about 120 km. The FPI temperature observations are consistent with the in situ rocket observations rather than the MSIS model.

Japanese sounding rocket "S-310-35" was launched from Andøya Rocket Range in Norway on December 13, 2004 during Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, in which the rocket-borne in-situ measurements and ground-based measurements were coordinated to carry out a comprehensive observation of the thermospheric response against the auroral energy input. The instruments on board the rocket successfully performed their measurements during the flight, and thereby the temperature and density of molecular nitrogen, auroral emission rate, and the ambient plasma parameters were derived. Simultaneous measurements by the ground-based instruments provided neutral wind, neutral temperature, the auroral images and the ionospheric parameters near the rocket trajectory. This paper introduces science objectives, experimental outline, and preliminary scientific results of the DELTA campaign and explains geophysical condition at the time of the rocket launch, while the companion papers in this special issue describe more detailed results from each instrument. 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.

In October 2003, a new space agency, JAXA (Japan Aerospace Exploration Agency) was reorganized and started as a primary space agency to promote all space activities in Japan. The Institute of Space and Astronautical Science (ISAS) belonged to JAXA and continued to promote space science and technologies using unique scientific satellites, sounding rockets and balloons. This paper summarizes sounding rocket and ballooning activities of ISAS in the fiscal year of 2003 and 2004, associated with satellite launch programs. In this time period, three sounding rockets and nineteen balloons were launched by ISAS. One of the sounding rocket, S-310-35 was an international collaboration between Japan and Norway, which was launched from Andoya Rocket Range (ARR), Andenes, Norway, so as to study the upper atmospheric dynamics and energetics associated with the auroral energy in the polar lower thermosphere. Through the combination with the national researchers and the cooperation with international organizations, ISAS will keep its own flight opportunities and be able to obtain many new scientific findings.

We present the solar activity dependence and seasonal variation of H+ and O+ polar wind velocity profiles observed by the suprathermal ion mass spectrometer (SMS) on Akebono. These observations spanned a solar cycle and covered a wide range of altitudes and invariant latitudes (ILAT) in the polar ionosphere and a variety of geomagnetic activity conditions from 1500 km to 8500 km altitude and from the poleward edge of the ionospheric trough (∼60° ILAT) to the polar cap (&gt 85° ILAT). At low (high) altitudes below (above) 4000 km, the increase of the averaged H+ and O+ ion velocities with altitude was larger (smaller) at solar minimum than at solar maximum. For example, the averaged H+ velocity on the dayside at 4000 km altitude was approximately 8 km s-1 at low solar activity but ∼5 km s-1 at high activity. This suggests that the averaged polar wind velocity correlates differently with solar activity and the dominant acceleration process may be different at low and high altitudes, respectively. For both H+ and O+ the observed ion velocity at high altitude was largest in the summer under essentially all magnetic and solar activity conditions. The O+ velocity at high altitude (&gt 4000 km) was significant and largest in the summer at solar maximum, when the solar energy input into the polar cap was largest theoretically, the velocity of O+ ions in the polar wind is expected to be negligible below 10,000 km. We consider geophysical processes that may contribute to the observed velocities and their solar activity and seasonal dependences, including the possible contributions of photoelectrons and elevated electron temperatures to the ambipolar electric field that drives the polar wind. Copyright 2004 by the American Geophysical Union.

A new approach is used to reveal the average thermal structure of plasmasphere at altitudes between 1000 and 10,000 km. This paper only considers the plasmasphere inside L = 3, and this region of space is sliced at L = 2 to one internal (denoted as equatorial) and one external (denoted as midlatitude) part. Each of these parts is divided into four altitude/local time zones: northern and southern daytime and northern and southern nighttime. Electron temperature (Te) distribution measured along every individual orbit within each zone is approximated by simple expressions that are functions of the geomagnetic latitude or L. The fitting is performed independently to each zone, and two coefficients are extracted from the individual fits: Te value at the equatorward border and the coefficient scaling the latitudinal shape. These coefficients are accumulated in each zone in order to obtain its average Te structure as a function of altitude. The fitting coefficients exhibit large scatter, which reflects the large day-to-day variability of plasmasphere Te. The fitting error is estimated at 6% and 12% for the equatorial and midlatitude zones, respectively. The average fit coefficients are used to check for seasonal variations in each zone and for a possible hemispheric asymmetry. It is determined that the winter sunlit plasmasphere is hotter than the summer one the case for nighttime is reverse. The day/night amplitude is larger in the winter than in the summer, and the seasonal differences are more pronounced in the Southern Hemisphere. The latitude gradients of Te reveal a hemispheric asymmetry, which is largest during northern daytime winter. Solar activity is found to affect the plasmasphere Te. During the day at 3000 km and L = 2, Te increases by ∼ 2000°K when F10.7 changes from 70 to 300. The nighttime increase is ∼1000°K. At the equator, Te shows weaker dependence on solar activity. The average heat flux through 3000 km altitude is estimated at 3.7 × 109 (eV cm-2 s-1) during the day and 1.6 × 108 (eV cm-2 s -1) during the night. Copyright 2002 by the American Geophysical Union.

中間圏及び下部熱圏高度における中性大気の力学過程は電離気体と密接な関係があるため,この高度領域での中性風の測定は重要である.今までは米国製マイクロロケット(バイパーロケット)から放出されたフォイル・チャフをレーダーで追尾することにより,単独で中性風の測定を行っていた.そこで複数の地球物理的なパラメータと同時に中性風の測定を行えるよう,観測ロケットからフォイル・チャフを放出する機構の開発を行い,下記の二通りの放出機構を試した.1)フォイル・チャフを封入した円筒を大気圧封じし,高度約100kmでの圧力差により放出する方法2)フォイル・チャフを封入した縦に割れ目の入った円筒をバネの力で放出し,竹割りの要領でフォイル・チャフを散布する方法それぞれの円筒には約5,000枚のフォイル・チャフを封入でき,ロケット側面から放出を行う.2000年1月10日に打ち上げられた観測ロケットS-310-29号機にフォイル・チャフ放出機構を搭載し,打ち上げ341秒後のロケット下降時に合計約20,000枚のフォイル・チャフを放出することに成功した.フォイル・チャフは一次レーダーモードで高度約95.0-88.5kmの間で追尾され,レーダーの情報から中性風の風向・風速が得られた.

During geomagnetically active times, the suprathermal mass spectrometer on the Akebono satellite frequently observes upflowing molecular ions (NO +, N2 +, Û2*) in the 2-3 Earth radii geocentric distance regions in the auroral zone. Molecular ions originating at ionospheric altitudes must acquire an energy of the order of 10 eV in order to overcome gravitation and reach altitudes greater than 2 RE. This energy must be acquired in a time short compared with the local dissociative recombination lifetime of the ions the latter is of the order of minutes in the F region ionosphere (300-500 km altitude). Upflowing molecular ions thus provide a test particle probe into the mechanisms responsible for heavy ion escape from the ionosphere. In this paper we analyze the extensive complement of plasma, field, and wave data obtained on the Akebono satellite in a number of upflowing molecular ion events observed at high altitudes (5000 -10,000 km). We use these data to investigate the source of energization of the molecular ions at ionospheric altitudes. We show that Joule heating and ion resonance heating do not transfer enough energy or do not transfer it fast enough to account for the observed fluxes of upflowing molecular ions. We found that the observed field-aligned currents were too weak to support large-scale field-aligned current instabilities at ionospheric altitudes. The data suggest but in the absence of high-resolution wave measurements in the 300 to 500 km altitude range cannot ascertain the possibility that a significant fraction of escape energy is transferred to molecular ions in localized regions from intense plasma waves near the lower hybrid frequency. We also compared the energization of molecular ions to that of the geophysically important O+ ions in the 300 to 500 km altitude range, where the energy transfer to O+ is believed to occur via small-scale plasma instabilities, ion resonance, and ion-neutral factional heating. Direct observation of energy input to the ionosphere from all of these sources in combination with in situ measurements of the density and temperature of neutral and ionized oxygen in the 300 to 500 km range are required to determine the relative importance of these energy sources in providing O+ with sufficient energy to escape the ionosphere. Copyright © 1994 by the American Geophysical Union.