阿部 琢美

This study compares the electron density and temperature observed by the CHAMP satellite and those predicted by the International Reference Ionosphere (IRI) model. The comparison has revealed a general agreement between CHAMP and IRI in the seasonal variation of the electron density and temperature. However, in polar regions, the model tends to overestimate the electron density and underestimate the electron temperature. In addition, the CHAMP observes a weaker winter anomaly in the southern hemisphere than in the nor-them hemisphere, while the IRI predictions are similar in both hemispheres. In the equatorial region, the model describes the dayside equatorial ionization anomaly fairly well, but underestimates its depth in the post-sunset local time sector by about 50%. In polar regions, two prominent spatial structures observed by CHAMP are found to be missing in the IRI prediction. Namely, a band of low electron density along the nightside auroral region and a band of elevated electron temperature near the cusp. The high-Te band near the cusp exhibits clear seasonal variation, with the largest latitude and local time coverage in summer and the smallest in winter. (C) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper presents an analysis of a large database of in-situ topside ionosphere electron densities (N-e) and temperatures (T-e) from three decades of satellite measurements with the ultimate goal of improving the International Reference Ionosphere (IRI) model. The satellite data, which range from the early Explorers to the more recent KOMPSAT and DMSP satellites, are examined to reveal the variation of the mid-latitude N-e and T-e at altitudes of 550, 850, and 2000 km as a function of solar activity for different local times, and seasons. Comparisons with IRI, the FLIP physical model, and the Millstone Hill incoherent scatter radar empirical model help to determine how consistent these satellite-observed variations patterns are with the current IRI model, with the theoretical expectations and with ground-based results. For N-e good agreement is found between the data and models in terms of variations pattern as well as absolute values. Whereas N-e always increases with solar activity, T-e can increase, decrease, or stay constant depending on the specific altitude, local time and season. At 550 km the daytime T-e increases with solar activity in summer, decreases in equinox and stays almost constant in winter. At this altitude range we find generally good agreement between the variations seen with the satellite data and those predicted by the FLIP and Millstone Hill models. At 850 km, however, significant discrepancies are noted. The satellite data, primarily DMSP in this altitude range, are consistently higher than the Millstone Hill model averages and include unrealistically high temperatures (4000-5000 K) at very low solar activities. The FLIP model also predicts much lower values at low solar activities but otherwise (for middle to high solar activities) agrees well with the satellite data. During nighttime the FLIP model underestimates T-e at 850 and 2000 km altitude for the summer and equinox seasons. The current IRI T-e model does not include variations with solar activity. The IRI values are generally in between the satellite and radar averages with a few exceptions. (C) 2007 Published by Elsevier Ltd on behalf of COSPAR.

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, similar to 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.

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 degrees 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.

This paper aims at describing the ionospheric conditions during the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign period based on EISCAT radar observations conducted at Tromsø (69.6°N, 19.2°E). We conducted EISCAT UHF radar observations on December 5 and from December 8 to December 13, 2004 with a beam-scanning mode for a total of 74 hours. Except for December 8 during a 2 hr interval operation, we operated the EISCAT UHF radar for 12 hour intervals everyday to make it possible to derive semidiurnal tidal amplitudes and phases in the lower thermosphere. Observed electron densities and derived electric fields by the EISCAT UHF radar indicate that magnetospheric activity was high during the period from December 5 to 13 except for the night of December 13. Derived semidiurnal amplitudes during December 9-12, 2004 exhibited a day to day variation at and below 110 km, while the corresponding phase was relatively stable over the four days except for the zonal component on December 12. Neutral and electron temperatures measured by the DELTA rocket were compared with neutral/ion and electron temperatures from the EISCAT UHF radar observations. Comparison of neutral/ion temperatures show some agreement, while poor agreements were found for the electron temperature. Possible causes of the discrepancy are discussed. 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 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.

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 (lambda(z) <5 km) and medium-scale (lambda(z) approximate to 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 similar to 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.

The coordinated sounding rocket and ground-based observations were conducted in Norway on 13 December 2004. The main objective of this campaign is to elucidate the dynamics and energetics in the lower thermosphere associated with the auroral energy input. The instruments on board the rocket successfully performed their measurements, and provided the temperature and density of molecular nitrogen, auroral emission rate, and the ambient plasma parameters, while neutral wind, neutral temperature, the auroral images and the ionospheric parameters were observed by ground-based measurements. In this paper, we present a summary of this campaign and preliminary results.

Overview and preliminary results of a coordinated rocket and ground-based measurement campaign, Waves in Airglow Structures Experiment 2004 (WAVE2004), are presented. The aim of the campaign is to understand the formation process of wavy structures in the airglow from both dynamical and chemical aspects. Na lidar was used to monitor the vertical structure of atmospheric waves continuously. Ground-based measurements operated from several days before the launch could detect various waves. The atomic oxygen density distribution found showed a single peak structure as usually expected instead of a double peak structure in the previous campaign. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

LHR band emissions observed at mid-latitude were investigated using data from the EXOS-C (Ohzora) satellite. A typical feature of the LHR band emissions is a continuous banded structure without burst-like and cut-off features whose center frequency decreases as the satellite moves to higher latitudes. A statistical analysis of the occurrence characteristics of the phenomena showed that midlatitude LHR emissions are distributed inside the plasmapause during magnetically quiet periods, and the poleward boundary of the emission region moves to lower latitudes as the magnetic activity increases. The attitude distribution of the waves suggests that the propagation in the LHR duct formed horizontally in the mid-latitude upper- ionosphere. The emission is closely related to the occurrence of ionospheric ELF hiss. It is also shown that LHR emissions are commonly observed in the slot region of the radiation belt, and they sometimes accompany the enhancement of the ionospheric electron temperature. The generation of the LHR band emissions is discussed based on the observed characteristics.

The polar cap ionosphere is known as a comparatively low-density (< 10(3) cm(-3) above 3000 kin) plasma region and less active than the cusp or auroral region in terms of particle precipitation. Because of the low density, very limited information on the thermal plasma in the high-altitude polar cap is available in the literature. On very rare occasions, the Akebono satellite encounters regions of unusually high-density plasma above 4000 km altitude, in which both the electron temperature (< 3000 K) and parallel ion drift velocity (< 1 km g(-1)) are distinctively low. The ion drift meter observations on the DMSP satellite show that the plasma convection in the polar cap is predominantly directed from the dayside to nightside on Such occasions, suggesting that anti-sunward convection is a necessary condition. The low electron temperature and ion velocity accompanied by the high plasma density may suggest that a small-amplitude ambipolar electric field is also another necessary condition for increasing the plasma density. (c) 2005 Published by Elsevier Ltd on behalf of COSPAR.

[1] 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 (similar to 60degrees ILAT) to the polar cap (> 85degrees 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 similar to5 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 (> 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.

The ISAS (Institute of Space and Astronautical Science) working group is currently studying the feasibility of a Venus orbiter mission [Proposal Report of feasibility study of Venus Climate Orbiter (in Japanese), ISAS working group, 2001], called PLANETC project, in which a 3 axis stabilized spacecraft will be launched in early 2008, and it will arrive at Venus in 2009. Primary purpose of the mission is to observe Venus climate so as to understand mechanism of the global circulation and three-dimensional motion of the Venus atmosphere in the lower stratum. In order to achieve the above scientific objectives, the spacecraft will carry several types of optical cameras mainly with near-infrared wavelengths. An accurate orientation for the attitude control is required in the spacecraft design. Furthermore, thermal control of the cameras is critical, because of large heat input from camera hoods and strict requirement of low temperature of detecting head. This paper describes characteristics of the PLANET-C spacecraft. And also depicted are the mission outline and the operation plan of the attitude orientation. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Inspection of electron temperature (T-e) profiles obtained by the thermal electron detector instrument along 5676 individual orbits of the Akebono satellite reveal the existence of localized structures with a latitude extent of 1-3theta. The analysis was constrained to the range 2 < L < 3.2 in the northern hemisphere within the period 1991-1997. Eighty-seven well-defined structures were selected, containing a marked increase of T-e at least 20% above the background level. The electron density (N-e) and the wave intensity at the upper hybrid resonance frequency, recorded by the plasma wave and sounder instrument on the same satellite, were also used in the analysis. It was found that N-e troughs and an increase of the electrostatic electron cyclotron harmonic waves perfectly co-located with the T-e structures. The structures were observed at altitudes above 3000 km, as 70% of them are found between 03 and 08 h magnetic local time. While the plasma inside the structures is always warmer, the plasma pressure can be either higher or lower than outside. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Average electron temperature (T,) distribution in altitude range 1000-10,000 km and in geomagnetic latitude range +/-70degrees are used to construct a simple analytical model of T-e. T-e distribution is considered constant during daytime (9-16 h) and nighttime (2204 h) local time sectors. Transition between the constant thermal states is described by cubic splines. The vertical Te profiles at fixed geomagnetic latitudes are approximated by second order polynomials and then the three constants of these polynomials are approximated by another set of analytical expressions, being explicit functions of altitude, geomagnetic latitude and local time. No seasonal variation or hemispheric asymmetry is considered in the model. The average T-e distributions at L shells greater than three were reconstructed, in order to avoid the unrealistically high temperatures measured in the regions with low plasma density. For this purpose, T-e distributions above 3000 km along the L shells were calculated, taking the gradients obtained at L = 2 (0.3 K/km during the day and 0.1 K/km during the night), reduced with latitudes as 1/(L-1). The accuracy and limitations of the model are discussed. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

[1] 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 2000degreesK when F-10.7 changes from 70 to 300. The nighttime increase is similar to1000degreesK. At the equator, Te shows weaker dependence on solar activity. The average heat flux through 3000 km altitude is estimated at 3.7 x 10(9) (eV cm(-2) s(-1)) during the day and 1.6 x 10(8) (eV cm(-2) s(-1)) during the night.

[1] The plasma density in the polar cap ionosphere is generally low (< 10(3) cm(-3) above 3000 km), mainly because of plasma escape from the ionosphere along open magnetic-field lines. The Akebono satellite occasionally encounters regions of unusually high plasma density (>= 10(3) cm(-3)) above 4000 km altitude, in which the thermal plasma exhibits a distinctively low electron temperature (< 3000 K) and low parallel ion drift velocity ( less than or equal to1 km/s). Such events are almost always observed on the dusk side. The occurrence of low electron temperature and ion drift velocity appears to suggest the antisunward convection of high-density plasma into the polar cap, and the decrease in electron temperature due to the disruption of field-aligned heat flux in the high-altitude polar cap.

A Venus orbiter mission is going to be proposed as one of the future Japanese planetary missions, The primary objective is to reveal the mechanism of the atmospheric general circulation. The mission will reveal also ionospheric circulation, atmospheric escape processes and geologic activities. The spacecraft will be launched in February-April of 2007 by a M-V rocket of ISAS and arrive at Venus in September of 2009. The spacecraft will be inserted into an elliptical equatorial orbit with a period of 21.3 hours. The outline of the mission is presented in this paper. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

We present proposals for observing the plasma transportation and circulation processes and the dynamics of the thermal plasmas that are the important element on Venus ionosphere by instruments installed on Venus Climate Orbiter. Main purpose of the observation is to elucidate the following unresolved problems: 1) How the upper atmosphere interacts with the lower atmosphere. 2) How much the energy of the solar wind can enter to the Venus upper atmosphere. 3) How momentum and energy of particles are transported into the upper atmosphere from external regions through the coupling process. In the presentation, the observation target and strategy will be discussed in detail.

We present a comparison of the electron density and temperature behavior measured in the ionosphere by the Millstone Hill incoherent-scatter radar during the period 25-29 June 1990, and in the plasmasphere within the Millstone Hill magnetic field flux tube by the instruments on board of the EXOS-D satellite in the Northern Hemisphere between 02:07:56 UT and 02:11:08 UT on 28 June 1990 with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere. We have evaluated the value of the nighttime additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite. The additional heating brings the measured and modeled electron temperatures into agreement with the plasmasphere and into very large disagreement with the ionosphere if the classical electron heat flux along magnetic field line is used in the model. The approach of Pavlov et al. (Annales Geophysicae 18 (2000) 1257-1272) based on an effective electron thermal conductivity coefficient along the magnetic field line, is used to explain the measured electron temperature in the ionosphere and plasmasphere. This approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere allow the model to accurately reproduce the electron temperatures observed by the instruments on board of the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The resulting effect of vibrationally excited N-2 and O-2 on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2. The modeled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 750 K at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without vibrationally excited N-2 and O-2, and inclusion of vibrationally excited N-2 and O-2 brings the model and data into better agreement. (C) 2001 Published by Elsevier Science Ltd.

記事種別: 会議・学会報告・シンポジウム

In the first part of this paper, we present observations of thermal H+ and O+ ion outflow in the middle to high altitude polar ionosphere from the Suprathermal ion Mass Spectrometer on Akebono satellite. Variations of H+ and O+ ion flux are given as a function of the geomagnetic activity or the interplanetary magnetic field for different magnetic local time or invariant latitude regions. 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 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 O+ ion flux was found to correlate positively with the Kp index. In the second part, simultaneous observations of the polar ion outflow is presented by using two instruments for thermal ions and electrons on the Akebono satellite and Sondrestrom radar in the polar ionosphere, with focussing on the dynamics of the ion outflow and its causal relationship to the plasma pressure profile. The drift velocity in the spin plane, plasma temperatures and number density are estimated from the satellite observation at high altitudes (greater than or equal to 1500 km), while at low altitudes (less than or equal to 900 km), these parameters are obtained from the radar observation. In the pass of 14h UT on Oct.15, 1992 (Kp=4(+)), high electron temperatures and low number density obtained from the satellite observations are in good agreement with the radar observation. In this event, the high velocity (similar to8 km/s at 2500 km) of the H+ outflow was significant, while lower velocity of the H+ was accompanied by low electron temperature and high density in the pass on Oct. 22, 1992 (Kp=3). Also, it should be noted that characteristic feature of the polar wind (T-e, T-i <1 eV) was successively observed as low as 70<degrees> invariant latitude. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

In the first part of this paper, we present observations of thermal H+ and O+ ion outflow in the middle to high altitude polar ionosphere from the Suprathermal ion Mass Spectrometer on Akebono satellite. Variations of H+ and O+ ion flux are given as a function of the geomagnetic activity or the interplanetary magnetic field for different magnetic local time or invariant latitude regions. 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 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 O+ ion flux was found to correlate positively with the Kp index. In the second part, simultaneous observations of the polar ion outflow is presented by using two instruments for thermal ions and electrons on the Akebono satellite and Sondrestrom radar in the polar ionosphere, with focussing on the dynamics of the ion outflow and its causal relationship to the plasma pressure profile. The drift velocity in the spin plane, plasma temperatures and number density are estimated from the satellite observation at high altitudes (greater than or equal to 1500 km), while at low altitudes (less than or equal to 900 km), these parameters are obtained from the radar observation. In the pass of 14h UT on Oct.15, 1992 (Kp=4(+)), high electron temperatures and low number density obtained from the satellite observations are in good agreement with the radar observation. In this event, the high velocity (similar to8 km/s at 2500 km) of the H+ outflow was significant, while lower velocity of the H+ was accompanied by low electron temperature and high density in the pass on Oct. 22, 1992 (Kp=3). Also, it should be noted that characteristic feature of the polar wind (T-e, T-i <1 eV) was successively observed as low as 70<degrees> invariant latitude. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20-30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N-2(nu) and O-2(nu) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N-2 and O-2 and the second level of O-2, and the calculated distributions of N-2(nu) and O-2(nu) are highly non-Boltzmann at vibrational levels nu > 2. The resulting effect of N-2(nu > 0) and O-2(nu > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N-2(nu > 0) and O-2(nu > 0), and inclusion of vibrationally excited N-2 and O-2 brings the model and data into better agreement.

中緯度スポラディックE層 (Es) の観測は古くから行われており, その生成機構についてはwind shear理論をもとに多くの研究がなされている。しかしEs付近の熱収支に関しては, 特に重要なパラメータの一つである電子温度の正確な測定例が少ないため, 未だ明確な議論がなされていない。今回, 観測ロケットS-310-27号機に搭載されたラングミュア・プローブにより, 高度92∿93kmに発生したEs付近の電子温度及び電子密度の測定を行った。電子密度の高度分布には, プローブ表面に太陽紫外線が照射されることによる2次電子の影響が如実に現れている。これを除去することによって, 大気波動に伴うwind shearが存在したことを示唆する波状構造が得られた。またEs付近の電子温度を算出した結果, Esピークではその前後と比べ数100Kの上昇を見せていることがわかつた。本報告書では, その依頼性について議論し, 今後Es形成機構及び熱収支を含めた研究に関する基礎的な情報を得ることを目的とする。

Measurements of electron temperature made by the thermal electron energy distribution (TED) instrument on board the EXOS-D (Akebono) satellite have been analysed. From the data taken between 1989 and 1995, averaged daytime and nighttime temperature profiles for different geophysical conditions have been produced. These profiles represent the averaged thermal electron temperature between 1000 and 8000 km altitude for conditions of high (F10.7 > 150) and low (F10.7 < 120) solar activity. Results indicate that increased solar activity has a marked effect on the electron temperature. At 8000 km altitude, the typical low-latitude daytime electron temperature is around 8000 K. The nighttime electron temperature at 8000 km is around 4000 K. The averaged daytime difference between high and low solar activity conditions is around 1000 K at altitudes above 2500 km. Between 1000 and 2000 km altitude this situation is reversed, and the electron temperature is comparatively higher during periods of low solar activity during both day and night. Composition changes in the region are proposed as a mechanism for this reversal. In addition, there is evidence of an asymmetry in thermal electron temperature between the northern and southern hemispheres. The averaged electron temperature is found to be comparatively higher in the northern hemisphere during the daytime and comparatively higher in the southern hemisphere during the nighttime. This difference between hemispheres is particularly evident during the nighttime, and during the rapid heating and cooling periods around sunrise and sunset. Possible reasons for the asymmetry are discussed. Profiles are also presented for conditio:ns of high (Ap>30) and low (Ap < 20) magnetic activity. Analysis has confirmed that geomagnetic activity has little effect on electron temperature below L = 2.2. (C) 1999 Elsevier Science Ltd. All rights reserved.

Japan's first Mars spacecraft PLANET-B was successfully launched on 4th of July 1998 and was named "NOZOMI" after the launch. One of the scientific instruments is a unique electron temperature probe which was developed in Japan and has been used for more than 20 years on sounding rockets as well as on scientific satellites (Oyama, 1991). The electron temperature probe dubbed PET (Probe for Electron Temperature measurements) consists of two planar electrodes, 150 mm in diameter, placed at the edges of the two solar cell panels of the "NOZOMI" spacecraft. Electron temperatures can be measured in plasmas with densities exceeding 1000 cm(-3) with sufficient accuracy. The maximum sampling rate of 8 data points per satellite spin for each probe allows high resolution measurements (i.e., an angular resolution around the spin axis of 23 degrees). Additionally, the probe can measure the anisotropy of the electron temperature, if it exists. It is also possible to infer the existence of nonthermal electrons.

我々はすでに、将来的にミリ波無線LAN等に期待されている60GHz帯において、室内のガラス窓等に使用すべく、抵抗被膜に着目した透明電波吸収体を実現している。しかし、透明性を有する電波吸収体は、レーザ周波数帯として重要なX帯用(8〜12GHz)においてもその必要性が高まってきている。そこで本研究では、抵抗被膜としてITO蒸着膜をガラスと一体形成し、これを空気層を介して2層構成にすることにより、特にレーダ周波数帯として重要なX帯をすべてカバーする広帯域な透明電波吸収体を実現することを試みた。この結果、理論計算を通して、ITO蒸着膜を用いて実現可能な面抵抗値の範囲内において、2層構成の透明電波吸収体が実現可能であることを確認するとともに、この検討結果をもとに設計・試作した2層構成の透明電波吸収体が、8.5〜11.5GHzにおいて低吸収領域でも17dBを越える良好な周波数特性を示すことを実験を通して確認した。