阿部 琢美

We present a method for estimating the thermal ion drift velocity, ion temperature, and spacecraft potential in the polar ionosphere from data acquired with the suprathermal mass spectrometer (SMS) on the Akebono satellite. The method is based on fitting the spin angle distributions of the observed ion flux for a number of retarding potential analyzer (RPA) settings to a drifting Maxwellian distribution. A nonlinear fitting procedure is used to relate the observed fluxes to the plasma parameters. The spacecraft potential is taken into account by means of the thin-sheath approximation. The analysis is applicable to the ''thermal'' (total energy few eV) polar wind ion population. A study of a number of representative passes at various altitudes, latitudes, and local times indicates that all major ions (H+ He+, and O+) have low temperatures, in the range of 0.05-0.35 eV, with little temperature dependence on altitude, longitude, or latitude. The velocity estimates confirm the previous analysis using the moment method: all ions have a significant upward velocity component (antiparallel to the magnetic field, in the northern hemisphere) which increases with altitude. The velocity estimates from data at the higher RPA settings are sometimes higher than those at low RPA settings. This indicates that the actual ion distributions are not Maxwellian, perhaps due to a higher-energy tail component drifting at higher velocity. All ions are in general supersonic at high altitudes.

マイクロ波ミリ波帯における材料の誘電率透磁率の測定においては, 摂動法を利用した共振器法や導波管内に充填した時に生じる定在波を用いて測定する導波管定在波法などが一般に知られている。しかし, これらの方法においでは測定時に共振器や導波管の寸法に合わせて, 測定試料を精度良く加工する必要があり, またこれらの加工精度に依存して測定された材料定数に誤差が含まれる事が知られている。我々は, これらの加工精度が測定値に与える影響について数値解析的に検討を行ってきたが, その結果として両者の関係を定量的に与えることが出来た。このような背景のもと, 測定試料を加工する事無く, 非破壊のまま測定を行う各種非破壊測定法が幾つか検討されてきた。本論文においては, 非破壊測定法を念頭に共振器法に着目し, 測定試料を加工する事無く共振器に挿入し, その際の共振周波数の変化から比誘電率を推定する方法について提案し理論的実験的検討を行っている。すなわち, 本測定法においては測定用の誘電体基板をそのままの状態で共振器に挿入するため, 加工精度や試料の凹凸などの不均一な形状に依存した誤差を格段に軽減する事が可能であり, また試料の加工プロセスを省略できるという二つの大きな利点をもっている。なお, 本実験で使用する矩形空洞共振器に誘電体試料を挿入した場合の共振周波数に関しては, 我々はすでにFDTD法を用いて計算を行っており, 得られた結果が実際に共振器に誘電率が既知の試料を挿入した際の周波数とかなり良い精度で一致することを確認している。特に本論文においてはこれに加えて共振器内部の電磁界分布を用いて共振器のQ値を計算し, 誘電率の虚部を推定する可能性についても言及している。

自由空間で電波吸収体の特性評価を行う場合、測定試料が測定周波数の波長に対して小さい場合が往々にして生じる。このような場合、その反射基準となる金属板や電波吸収体自体からの反射特性が変化し、正確な特性評価が困難となることが予想される。そこで本研究においてはFDTD法による電磁界シミュレーションを行い、平面波に対向して置かれた電波吸収体の大きさの変化に対応する反射減衰量の変化を数値解析的に検討している。

Electron temperature variations in the Earth's plasmasphere are studied using the EXOS-D satellite observations and the Sheffield University plasmasphere-ionosphere model. The observations made during 1989-1994 are analysed to investigate the local time and altitude (1000-8000 km) variations of electron temperature at magnetic latitudes 0-45 degrees N. The observed electron temperature, T-c is almost constant during both day and night and is found to have large day-to-night differences that vary with altitude and latitude; the largest difference (similar to 6500 K/2600 K) occurs at the highest altitude at equatorial latitudes and the smallest difference (similar to 3300 K/2300 K) at the lowest altitude at mid latitudes. During daytime, T-c increases rapidly with altitude in the lower plasmasphere (altitude <2500 km) and slowly in the upper plasmasphere with mean gradients of 1.33 K km(-1) and 0.22 K km(-1), respectively. At night, on the other hand, the lower plasmasphere is in thermal equilibrium and in the upper plasmasphere T-c increases slowly with a mean gradient equal to the daytime value. (C) 1997 COSPAR. Published by Elsevier Science Ltd.

The electron temperature T-e in the Earth's plasmasphere up to 10,000 km altitude, has been measured routinely by a thermal electron energy distribution instrument on board the EXOS D satellite. The measurements made during the years 1989-1995 have been analyzed to obtain altitude (1000-8000 km) profiles of T-e for magnetic latitudes 0 degrees-40 degrees N at different times of the day. The profiles are compared with those computed by the Sheffield University plasmasphere-ionosphere model, modified to include nonlocal heating due to trapped photoelectrons and an equatorial high-altitude heat source. The photoelectrons are trapped at altitudes above 600 km, and the high-altitude heat source is applied as energy input along the magnetic field lines with apex altitude greater than 600 km between +/-10 degrees magnetic latitude. The results for 8000 km altitude show that the modeled values of T-e computed without photoelectron trapping and the high altitude heat source are much less than the mean measured values, 3700 K compared with 6500 K. Depending upon altitude and latitude, a photoelectron trapping of up to 100% is required to raise the modeled electron temperatures to the mean measured values. However, photoelectron trapping alone cannot account for the observed latitude variation of T-e, which depends on altitude. Model calculations carried out with 50% photoelectron trapping and an altitude and local time-dependent high-altitude heat source reproduce the measurements, including the latitude variation; the heat source required for nighttime is about one fourth of that required for daytime. An equatorial high-altitude heat source appears to be the only mechanism that can account for the measured values of T-e; values in excess of 12,000 K have been measured. There are some quantitative differences between the measured and modeled temperatures at night in the lower plasmasphere (<2500 km), which could be caused, in whole or in part, by the inaccuracies of the nighttime measurements due to the low plasma densities.

本研究においては簡便な誘電率測定法として用いられる共振器法について、測定用の試料を加工する事なく挿入し、共振周波数から誘電率を推定する方法について提案を行っている。特にここでは、実在する矩形空洞共振器にスリットを設け薄型誘電体基板を挿入し実験的に共振周波数を求めるとともに、これらを数値的にモデル化しFDTD法を用いた数値解析により内部の電磁界の時間的変化から共振周波数を計算し、両者を比較する事によって本研究で用いている手法の妥当性を検討している。 解析結果によれぱ、計算から得られた共振器内部電磁界の共振周波数は、実験的に求められた測定値と僅かの誤差範囲内で一致し、解析対象に対する本手法の有効性を確認出来た。本解析手法は今後、様々な試料形状に対して応用が考えられ、試料を加工せずに誘電率測定を可能にする方法として成果が期待される。

Electron temperature variations in the Earth's plasmasphere are studied using the Exos D satellite observations and the Sheffield University plasmasphere-ionosphere model. The observations made during the years 1989-1994 are analyzed to investigate the local time and altitude (1000-8000 km) variations of the electron temperature at magnetic latitudes 0 degrees-45 degrees N. The observed electron temperature T-e is almost constant during both day and night and is found to have large day-to-night differences that vary with altitude and latitude; the largest day-to-night ratio in T-e (approximate to 6500 K/2600 K) occurs at the highest altitude at equatorial latitudes and the smallest ratio (approximate to 3300 K/2300 K) at the lowest altitude at midlatitudes. During daytime, T-e increases rapidly with altitude in the lower plasmasphere (altitude <2500 km) and slowly in the upper plasmasphere with mean gradients of 1.33 and 0.22 K km(-1), respectively. At night, on the other hand, the lower plasmasphere is in thermal equilibrium, and in the upper plasmasphere T-e increases slowly with a mean gradient equal to the daytime value. The electron temperature shows maximum latitude variation at medium plasmaspheric altitudes (around 4000 km) and smaller variations at lower and higher altitudes, particularly during daytime. At the altitude of maximum latitude variation, T-e increases by about 1200 K between the equator and 40 degrees N during both day and night. The model reproduces the observations reasonably well and is used to explain the occurrence of a prominent morning peak in T-e. The morning peak becomes prominent in the lower plasmasphere at low latitudes because of the vertical E x B drift in the equatorial F region, which increases T-e during morning hours and decreases T-e during daytime hours. The observations and model results also show the occurrence of an afternoon peak in T-e, which becomes prominent with increasing altitude and latitude; the peak could be caused by the daytime poleward neutral wind.

誘電率透磁率の測定には共振器法や導波管定在波法などが一般に知られているが、これらにおいては測定時に共振器や導波管の寸法にあわせて、試料を精度良く加工する必要があり、精度が低下すると測定値に大きな誤差が含まれる事が知られている。本研究においては、測定試料を加工する事無く、非破壊のままでの測定法として、共振器法を応用し、厚さ1〜2mmの誘電体基板を加工する事無く共振器に挿入し、その際の共振周波数の変化から比誘電率を推定する方法について提案し、その理論的実験的検討を試みた。

FDTD法は、電磁界の過渡的状態から定常状態に至る時間的変化を観察できるため、最近アンテナ、導波管、共振器問題等の各種の分野において利用されている。そこで本研究では、このFDTD法を共振器を用いた透磁率測定に応用すべく、その基礎的検討として、TE_102矩形共振器の共振周波数を計算し、この値から透磁率を推定し、その有効性の検討を行った。

FDTD法は、電磁界の過渡状態から定常状態にいたるまでの振るまいを観察できるため、最近アンテナ、導波管、共振器問題等の各種の分野において利用されている。そこで、本研究では、このFDTD法を用いて、今後誘電率の測定に利用すべく、TE_<101>モード矩形共振器のQ値の計算を試みた。この結果、理論値と比較しても、5%以下程度の誤差で良好な一致がみられ、FDTD法のQ値の計算に対する有好性が確認できた。

The frequent occurrence of energetic O+ upflowing ionospheric ions (UFI) at high altitude during auroral substorms raises the question of the cold plasma source and acceleration altitude for the O+ ions, and their possible effects on the substorm-time plasma sheet. Ion composition observations on Akebono in the nightside auroral ionosphere reveal the significant presence of thermal-energy (a few eV) O+ ions in the 6000-10,000 km altitude region both during and between auroral substorms. Their upward flux normalized to 2000 km altitude is about 2 x 10(8) cm(-2) s(-1). They are believed to be a significant source of cold plasma for the energetic UFI. During auroral substorms, Akebono occasionally observes molecular (N-2(+) and NO+) upflowing ions up to similar to 60 eV, in or near regions of auroral electron precipitation up to 10,000 km altitude. This suggests the occurrence of a fast ion acceleration process in the F-region or topside ionosphere, where freshly created molecular N-2(+) and NO+ ions are accelerated to several eV or greater within their dissociative recombination lifetime (similar to a few minutes). Ground photometric observations and simultaneous particle measurements on sounding rockets confirm the presence of transversely accelerated ions (TAI) up to similar to 200 eV in the topside ionosphere (near 600 km altitude) within tens of seconds of substorm expansion onset. Such hundred-eV TAI are frequently observed on Akebono in latitudinally confined regions of the nightside auroral ionosphere down to similar to 2000 km altitude. They can reach the so-called ''parallel acceleration region'' at similar to 1-2 R(E) altitude within a few minutes, where they are often accelerated further to keV energy and can typically reach the plasma sheet during a substorm. Their flux is an order of magnitude smaller than the thermal ion flux. They are believed to be a minor source of plasma for the energetic UFI. In contrast, the lower-energy (less than or equal to 10-eV) O+ TAI are typically too slow to reach the parallel acceleration region during the substorm, as they are decelerated by gravitation or trapped by it and traverse repeatedly along the magnetic field line. Hence they constitute a possible source of quiet-time thermal ions in the parallel acceleration region. Another possible source of thermal ions in the region is the polar wind O+ ions convected anti-sunward along the auroral oval from the dawn and dusk sectors. The thermal O+ ions in the parallel acceleration region at similar to 1-2 R(E) altitude of the nightside auroral ionosphere are believed to be the dominant source of cold plasma for energetic UFI at high altitude; they can reach the plasma sheet during a substorm, thereby modifying its composition significantly.

We present a statistical analysis of thermal H+ and O+ ion flux measurements in the high-altitude (6000 similar to 9000 km) polar ionosphere from the Suprathermal ion Mass Spectrometer (SMS) on Akebono. It is shown that the normalized H+ polar wind flux (to 2000 km altitude) varies from 10(7) to 10(8) cm(-2) s(-1) at 2000 km altitudes. Surprisingly, the O+ ion flux is found to be comparable to the H+ ion flux and much higher than classical theory prediction. The magnetic local time (MLT) distribution of the upward ion flux and its geomagnetic activity (K-p) dependence are also presented. At both magnetically quiet and active times, the integrated H+ ion flux is largest in the noon sector (09 similar to 15 MLT) and smallest in the midnight sector (21 similar to 03 MLT); the flux ratio was found to be approximately one order of magnitude. The total flux of H+ ion outflow integrated over the polar ionosphere (ILAT greater than or equal to 75 degrees) and over all local times was found to correlate inversely with the K-p index. The integrated H+ flux (ILAT greater than or equal to 75 degrees) in quiet times was 0.9 similar to 1.5 x 10(25) ions s(-1) while the flux in active times was a factor of 2 similar to 3 smaller (0.4 similar to 0.6 x 10(25) ions s(-1)). It also exhibited a slight positive correlation with the IMF (interplanetary magnetic field) B-z component.

We present an overview of direct ion and electron observations of the polar wind and suprathermal auroral ions from the plasma instruments on Akebono. In the polar wind, the observed H+ ion reaches a velocity of 1 km/s at 2000 km altitude, as does He+ ion near 3000 km and O+ ion near 6000 km. At high altitudes, the O+ ion constitutes a significant component of the polar wind flow contrary to most polar wind model predictions. At 2000-4000 km, the H+ ion velocity in the polar wind is strongly correlated with the ambient electron temperature. The electron temperature (averaged thermal energy) in the upward magnetic field direction is a factor of 1.5-2 higher than that in the downward and field-perpendicular directions. This results in an upward heat flux which is comparable in magnitude to the heat flux carried by energetic (&gt; 10-eV) photoelectrons. The observed electron temperature anisotropy and correlation with ion velocity are consistent with the polar wind being driven by a large ambipolar electric field resulting from the presence of escaping atmospheric photoelectrons (required to maintain quasineutrality along the field line). At auroral latitudes, significant fluxes of &apos;&apos;minor ions&apos;&apos; are frequently observed, particularly atomic N+ and O++ ions and molecular NO+, N-2(+), and O-2(+) ions. The occurrence of molecular ions at high altitude (&gt; 3000 km) during extended periods of auroral activity points to their fast energization at the F-region and topside ionosphere. In the 3000-6000 km altitude region, transverse ion energization occurs frequently both on the dayside and the nightside. Different ion species are energized in the perpendicular direction to tens and at times hundreds of eV over a narrow spatial extent, and appear as &apos;&apos;ion conics&apos;&apos; at higher altitudes as they spiral up the field lines. In the 3000-9000 km altitude region, the average energy of the observed ion conics in the dayside auroral zone increases with altitude.

We present a statistical analysis of thermal H+ and O+ ion flux measurements in the high-altitude (6000 similar to 9000 km) polar ionosphere from the Suprathermal ion Mass Spectrometer (SMS) on Akebono. It is shown that the normalized H+ polar wind flux (to 2000 km altitude) varies from 10(7) to 10(8) cm(-2) s(-1) at 2000 km altitudes. Surprisingly, the O+ ion flux is found to be comparable to the H+ ion flux and much higher than classical theory prediction. The magnetic local time (MLT) distribution of the upward ion flux and its geomagnetic activity (K-p) dependence are also presented. At both magnetically quiet and active times, the integrated H+ ion flux is largest in the noon sector (09 similar to 15 MLT) and smallest in the midnight sector (21 similar to 03 MLT); the flux ratio was found to be approximately one order of magnitude. The total flux of H+ ion outflow integrated over the polar ionosphere (ILAT greater than or equal to 75 degrees) and over all local times was found to correlate inversely with the K-p index. The integrated H+ flux (ILAT greater than or equal to 75 degrees) in quiet times was 0.9 similar to 1.5 x 10(25) ions s(-1) while the flux in active times was a factor of 2 similar to 3 smaller (0.4 similar to 0.6 x 10(25) ions s(-1)). It also exhibited a slight positive correlation with the IMF (interplanetary magnetic field) B-z component.

本研究においては簡便な誘電率測定法として用いられる共振器法について、測定用の試料を加工する事なく挿入し、共振周波数から誘電率を推定する方法について提案を行い、その基礎的な理論的検討を行っている。測定試料は厚さ0.75〜3.25mmの誘電体薄型基盤を想定し、共振器の中央部に垂直に挿入させ、その際の電磁界をFDTD法により計算した。解析結果によれば、共振器内部電磁界の共振周波数から得られた誘電率は、理論的な等価回路を用いて計算される理論値と僅かの誤差範囲内で一致し、本解析対象に対するFDTD法の有効性を確認出来た。本解析結果は今後、様々な試料の形に対しての応用が考えられ、試料を加工せずに誘電率測定を可能にする方法として、その成果が期待される。

We report Akebono observations of anisotropic electron velocity distributions in the sunlit polar wind, in which the averaged energy (temperature) of the thermal energy electrons is higher in the upward magnetic field direction than in the downward and perpendicular directions. In the 1500-4000 km altitude region, the observed upward to downward temperature ratio: T-eu/T-ed, was in the range of 1.5 to 2. The observed downward and perpendicular temperatures were similar; T-ed/T-e perpendicular to similar or equal to 1 The heat flux associated with the observed thermal energy electron velocity distribution was upward and on the order of similar to 10(-2)erg cm(-2)s(-1), and was a factor of 5 larger than that of the atmospheric photoelectrons above 10 eV. In this altitude region, the higher-energy (&gt; a few eV) photoelectrons are essentially collisionless. In contrast, the ambient and lower-energy photoelectrons remain collisional because of their larger Coulomb collision cross sections. In the steady state, an ambipolar electric field is required to maintain quasi-neutrality along the field line. It is suggested that the ambipolar electric field and the Coulomb collisions modify the velocity distributions of the thermal energy electrons and the photoelectrons, resulting in the observed temperature anisotropy. The upward heat flux associated with the observed temperature anisotropy dominates any downward heat flux due to electron temperature gradients that may be present in the polar wind plasma and demonstrates the important role of the photoelectrons in the dynamics of the polar wind.

本研究においては、3次元の電磁界解析法として有効なFDTD法を導波管内の電磁界解析に応用し、導波管定在波法を用いた誘電率測定において、特に測定試料の変形に起因する誤差について検討した。ここで、解析モデルとしては、導波管定在波法の中でも一般的によく使用されているTE_<10>モードによる方形導波管を用いた短絡法に着目し、挿入試料の誘電率と変形度をパラメータとして誤差の検討を行なった。この結果、このような導波管内の電磁界解析に対してFDTD法が有効であること、また挿入試料の誘電率および変形度と誘電率測定における誤差には明確な相互間が示され、今後、本方法を用いた誘電率測定における誤差測定に対して有効な資料が得られた。

摂動法による矩形空洞共振器を用いた誘電率、透磁率の測定においては、試料が大きいか、あるいはその誘電率が大きい場合には摂動法の仮定が成り立たなくなることから、大きな誤差が生じることが知られている。筆者らは、この誘電率測定について、試料の大きさと誘電率による依存性について既に報告を行った。しかし、実際の誘電率測定においては、微少試料を空洞共振器内部に設置するため、共振器壁には挿入孔が存在する。本来、空洞共振器にはその寸法に固有の共振周波数が与えられるが、試料挿入孔の存在によってその構造が変化するため、誘電率の推定に影響を与えることが予想される。そこで本研究においては、3次元の電磁界解析手法として有効なFDTD法を空洞共振器に適用し、試料挿入孔が誘電率測定に与える影響について検討を行なっている。

With a special set of planar probes, the Japanese satellite, AKEBONO has continued electron temperature (Te) measurement up to the height of similar to 10000 km in all latitude ranges, since its launch in 1989. Although the data are still being analyzed and the results obtained so far are preliminary, we discuss the height profiles in the latitude range which is lower than 60 degrees, in terms of local time, geomagnetic latitude and seasonal variations. Although quite a large amount of theoretical work on the thermal structure of the high altitude has been done so far, the results obtained by means of the satellite AKEBONO, present a first systematic picture of the inner plasmasphere of the earth.

The Suprathermal ion Mass Spectrometer (SMS) on EXOS-D frequently observed the energy distributions of both thermal and suprathermal ions in and near Transverse Ion Energization (TIE) regions. TIE frequently occurs at low energies (&lt;20 eV) near the dayside cusp or auroral regions at high altitude (&gt;2000 km) over a latitudinal range less than similar to 50 km. In TIE regions, all (major and minor) ion species are energized to approximately the same energy perpendicular to the local magnetic field and expand outward along the magnetic field line forming conical ion distributions. Therefore, a TIE region is characterized by the occurrence of ion conics peaking at 90 degrees pitch angles. From the measured thermal ion energy distributions, we estimated the ion velocity parallel and perpendicular to the magnetic field, density and temperature for the individual species in and near TIE regions. We found that the TIE occurs in the velocity shear region between eastward and westward plasma convection. In the dayside region, field-aligned flow of light (H+ and He+) ions is often observed equatorward of the TIE region; the characteristic of this flow is consistent with classical polar wind. In contrast, poleward of the TIE region, O+ is often a major component of the polar wind flow.

Electron temperatures up to 8000km were observed by the Japanese scientific satellite ''AKEBONO'' which was launched in 1989 with an inclination of 75 degrees. Since launch,satellite data have been recorded at four tracking stations; Kagoshima in Japan, Esrange in Sweden, Prince Albert in Canada, and Shows in Antarctica. The observations cover latitudes up to 75 degrees,for all longitudes and local times. The paper mainly describes features of the height profiles of electron temperature, with regards to variations in local time, latitude and season. The intent is to contribute to the construction of a model of electron temperature at altitudes over 1000 km.

During geomagnetically active times, the suprathermal mass spectrometer on the Akebono satellite frequently observes upflowing molecular ions (NO+, N-2(+), O-2(+)) 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 R(E). 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 frictional 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.

最近のミリ波電波吸収体の必要性にともない、我々はすでに抵抗皮膜をスペーサを介して構成した抵抗皮膜型ミリ波電波吸収体について、各種の設計チャートを提案し、その有効性を実験を通して確認した。しかし、実際にこのタイプの吸収体を制作する場合、抵抗皮膜の面抵抗値やこれを保持するスぺーサの厚みの制御が難しく、実用的にはこれらの誤差の反射減衰量ヘの影響を検討する必要がある。そこで本報告では、抵抗皮膜の面抵抗値とスペーサの厚みの誤差が製作した吸収体の反射減衰量にどの程度影響するかについて検討し、構成及び製作法について、これらの誤差影響も含めた実用的な各種の設計チャートを示した。なお、この吸収体の構成及び制作法(図1)については文献[2]に詳細に示されている。[figure]

We present Akebono observations of the polar wind velocity and the ambient electron temperature in the polar ionosphere. The velocity of the H+ polar wind increases from about 1 km/s at 2000 km altitude to about 6 km/s at 4000 km altitude, and correlates with the local electron temperature at a given altitude. It is only weakly dependent on magnetic activity, but is generally more variable at active times. Our observation demonstrates the direct relationship between the local magnitude of ion acceleration and that of the ambipolar electric field responsible for the acceleration.

On January 28, 1990, the Dynamics Explorer 1 and Akebono satellites crossed a magnetic field structure at the equatorward edge of the polar cusp at altitudes of 22,000 and 5000 km, respectively, within 6 min of each other. Locally measured plasma particles and fields and magnetometer data from a ground station near the foot of the magnetic field line are more consistent with an interpretation of the structure as that of a standing Alfven wave than that of a quasi-steady field-aligned current sheet. We discuss the observations supporting this conclusion and other related observations of field-aligned currents, Alfven waves, and ion energization near the equatorward edge of the cusp. These observations suggest that Alfven waves are commonly present near the equatorward edge of the cusp.

We present Akebono observations of the polar wind velocity and the ambient electron temperature in the polar ionosphere. The velocity of the H+ polar wind increases from about 1 km/s at 2000 km altitude to about 6 km/s at 4000 km altitude, and correlates with the local electron temperature at a given altitude. It is only weakly dependent on magnetic activity, but is generally more variable at active times. Our observation demonstrates the direct relationship between the local magnitude of ion acceleration and that of the ambipolar electric field responsible for the acceleration.

本報告では、従来回転物体のレーダ断面積の測定法として検討されたレンジドップラーイメージング法に着目し、この方法を応用して一般的な室内において電波吸収体の測定評価をどの程度、高精度に行うことができるかについて検討した。この結果300×300mmの金属板からの反射レベルに比較して40〜50dBの測定可能範囲が得られること及び測定した吸収量の測定値と理論値は良好に一致することがわかり、本方法が一般的な室内において吸収体の特性評価に有効であることを実験的に確認した。

In the high-altitude polar cap, the suprathermal ion mass spectrometer (SMS) On the satellite frequently ''observed'' ion depletion zones (IDZ) in which the thermal-energy ion flux was below the detection limit of SMS, corresponding to thermal-energy ion densities less than 10(-2) cm-3. These IDZ are located primarily in the nightside region of the magnetosphere at invariant latitudes above 70-altitude and at altitudes preferentially near apogee and between 8000 and 10,000 km (EXOS D apogee) but extending down to 3000 km. In contrast outside the IDZ, the SMS regularly observed outflowing H+, He+, O+, and O++ polar wind ions with energies typically less than 10 eV in the polar cap. Also, at sufficiently low altitudes below the IDZ the SMS instrument always observed H+, He+, O+, and O++ ions that were stationary in the Earth's corotating frame, i.e., ions observed in the spacecraft ram direction.

We report observations of the H+, He+, and O+ polar wind ions in the polar cap(&gt;80-degrees invariant latitude. ILAT) above the collision-dominated altitudes (&gt;2000 km), from the suprathermal mass spectrometer (SMS) on EXOS D (Akebono). SMS regularly observes low-energy (a few eV) upward ion flows in the high-altitude polar cap, poleward of the auroral oval. The flows are typically characteristic of the polar wind, in that they are field-aligned and cold (T(i) &lt; 10(4) K-degrees), and the parallel (field-aligned) velocities of the different ion species vary inversely with the respective ion masses. A statistical study of the altitude, invariant latitude, and magnetic local time distributions of the parallel velocities of the respective ion species is described, and preliminary estimates of ion temperatures and densities, uncorrected for perpendicular drifts and spacecraft potential effects, are also presented. For all three ion species, the parallel ion velocity increased with altitude. In the high-latitude polar cap (&gt;80-degrees ILAT), the average H+ velocity reached 1 km/s near 2000 km, as did the He+ velocity near 3000 km and the O+ velocity near 6000 km. At Akebono apogee (10,000 km), the averaged H+, He+, and O+ velocities were near 12,7, and 4 km/s. respectively. Both the ion velocity and temperature distributions exhibited a day-to-night asymmetry, with higher average values on the dayside than on the nightside.

Observations by the thermal electron energy distribution (TED) instrument on board the Akebono (EXOS - D) satellite show that variations in electron temperatures, at altitudes from 300 to 2300 km, are closely related to field-aligned current (FAC) structures. At higher altitudes, electron temperatures increase in upward FAC regions and decrease in regions of downward FAC, while at the lower altitudes only temperature increases in upward FAC and adjacent regions are observed. Electron temperature variations were also found to be related to the number density of ambient electrons and the field-aligned current density. A numerical simulation is carried out to examine energetic particle precipitation and Joule dissipation as a possible mechanism for the observed temperature variations using the electron energy equation. In the present study, we focus the simulations on the temperature increase. Thermal electrons are found to be efficiently heated by Joule dissipation at lower altitudes; however, for increasing altitudes, energetic particle precipitation becomes the major heating source. These conclusions are supported by TED observations at low altitudes (&lt;500 km); however, an additional heat source is required to explain the observed higher-altitude (&gt;800 km) temperature increases.

We report observations of the H+, He+, and O+ polar wind ions in the polar cap(&gt;80-degrees invariant latitude. ILAT) above the collision-dominated altitudes (&gt;2000 km), from the suprathermal mass spectrometer (SMS) on EXOS D (Akebono). SMS regularly observes low-energy (a few eV) upward ion flows in the high-altitude polar cap, poleward of the auroral oval. The flows are typically characteristic of the polar wind, in that they are field-aligned and cold (T(i) &lt; 10(4) K-degrees), and the parallel (field-aligned) velocities of the different ion species vary inversely with the respective ion masses. A statistical study of the altitude, invariant latitude, and magnetic local time distributions of the parallel velocities of the respective ion species is described, and preliminary estimates of ion temperatures and densities, uncorrected for perpendicular drifts and spacecraft potential effects, are also presented. For all three ion species, the parallel ion velocity increased with altitude. In the high-latitude polar cap (&gt;80-degrees ILAT), the average H+ velocity reached 1 km/s near 2000 km, as did the He+ velocity near 3000 km and the O+ velocity near 6000 km. At Akebono apogee (10,000 km), the averaged H+, He+, and O+ velocities were near 12,7, and 4 km/s. respectively. Both the ion velocity and temperature distributions exhibited a day-to-night asymmetry, with higher average values on the dayside than on the nightside.