阿部 琢美

Ion sheath which is formed around an electrode significantly affects the impedance of the probe immersed in a plasma. The sheath capacitances obtained from impedance probe measurements were examined for application to plasma diagnoses. We compared analytical calculations of the sheath capacitance with measurements from impedance probes onboard ionospheric sounding rockets. The S-520-23 sounding rocket experiment, which was carried out in mid-latitude, demonstrated that the observed sheath capacitances agreed well with those of the calculations. We concluded that the sheath capacitance measurements allow for estimation of the electron temperature and the electron density of a Maxwellian plasma. On the other hand, the sheath capacitances obtained from the S-310-35 rocket experiment in the auroral ionosphere showed lower values than expected. Auroral particles precipitations should modify the probe potential.

A coordinated observation of the atmospheric response to auroral energy input in the polar lower thermosphere was conducted during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign. N2 rotational temperature was measured with a rocket-borne instrument launched from the Andøya Rocket Range, neutral winds were measured from auroral emissions at 557.7 nm with a Fabry-Perot Interferometer (FPI) at Skibotn and the KEOPS, and ionospheric parameters were measured with the European Incoherent Scatter (EISCAT) UHF radar at Tromsø. Altitude profiles of the passive energy deposition rate and the particle heating rate were estimated using data taken with the EISCAT radar. The local temperature enhancement derived from the difference between the observed N2 rotational temperature and the MSISE-90 model neutral temperature were 70-140 K at 110-140 km altitude. The temperature increase rate derived from the estimated heating rates, however, cannot account for the temperature enhancement below 120 km, even considering the contribution of the neutral density to the estimated heating rate. The observed upward winds up to 40 m s-1 seem to respond nearly instantaneously to changes in the heating rates. Although the wind speeds cannot be explained by the estimated heating rate and the thermal expansion hypothesis, the present study suggests that the generation mechanism of the large vertical winds must be responsible for the fast response of the vertical wind to the heating event. Copyright 2009 by the American Geophysical Union.

In order to investigate the dynamics of the mesopause region, foil chaff experiments were carried out successfully during the WAVE2000 and WAVE2004 campaigns at Kagoshima, Japan. In the WAVE2004 campaign, the height profiles of the horizontal and vertical wind speeds were obtained. The wind shear layers of &gt 40 m/s/km were located around the altitudes of 89 and 95 km, and the profile of the Richardson number reveals the existence of dynamically unstable layers at about the same height region. Ripple observations using the all-sky imagers also support the possibility of dynamical instabilities. In the WAVE2000 campaign, a prominent small-scale feature around an altitude of 90.5 km appeared in both the horizontal and vertical chaff motions. These results demonstrate that the foil chaff technique is a valuable tool for in situ observation of small-scale turbulence features around the mesopause. Copyright 2009 by the American Geophysical Union.

The Venus Climate Orbiter mission (PLANET-C), one of the future planetary missions of Japan, aims at understanding the atmospheric circulation of Venus. Meteorological information will be obtained by globally mapping clouds and minor constituents successively with 4 cameras at ultraviolet and infrared wavelengths, detecting lightning with a high-speed imager, and observing the vertical structure of the atmosphere with radio science technique. The equatorial elongated orbit with westward revolution fits the observation of the movement and temporal variation of the atmosphere which rotates westward. The systematic, continuous imaging observations will provide us with an unprecedented large dataset of the Venusian atmospheric dynamics. Planet-C will be launched in 2010 and will reach Venus in 5 months. Nominal operation period is 2 earth years.

The electron temperature (T(e)), electron density (N(e)), and two components of the electric field were measured from the height of 90 km to 150 km by one of the sounding rockets launched during the SEEK-2 campaign. The rocket went through sporadic E layer (E(s)) at the height of 102 km-109 km during ascent and 99 km-108 km during decent, respectively. The energy density of thermal electrons calculated from N(e) and T(e) shows the broad maximum in the height range of 100-110 km, and it decreases towards the lower and higher altitudes, which implies that a heat source exists in the height region of 100 km-110 km. A 3-D picture of E(s), that was drawn by using T(e), N(e), and the electric field data, corresponded to the computer simulation; the main structure of E(s) is projected to a higher altitude along the magnetic line of force, thus producing irregular structures of T(e), N(e) and electric field in higher altitude.

Electron temperature in the sporadic E layer was measured with a glass-sealed Langmuir probe at a midlatitude station in Japan in the framework of the SEEK (Sporadic E Experiment over Kyushu)-2 campaign which was conducted in August 2002. Important findings are two fold: (I) electron temperature and electron density vary in the opposite sense in the height range of 100-108 km, and electron temperature in the E, layer is lower than that of ambient plasma, (2) electron temperature in these height ranges is higher than the possible range of neutral temperature. These findings strongly suggest that the heat source that elevates electron temperature much higher than possible neutral temperature exists at around 100km, and/or that the physical parameter values, which are used in the present theory to calculate electron temperature, are not proper.

Two projects are introduced in this paper to verify the performance of space tether technology. A sounding rocket will be launched in the summer of 2009 to deploy a bare electro-dynamic tape tether having a length of 300 m. The other project to verify the space tether technology is a small satellite to deploy a bare 25 km electro-dynamic tape tether, and the launch is expected in 2013 with employing a new solid motor rocket. These verifications of tether technology will lead to a large numbers of applications of space tether technology and some future projects are also introduced. 資料番号: AA0063706026

The polar wind is an ambipolar outflow of thermal plasma from the high-latitude ionosphere to the magnetosphere, and it primarily consists of H+, He+ and O+ ions and electrons. Statistical and episodic studies based primarily on ion composition observations on the ISIS-2, DE-1, Akebono and Polar satellites over the past four decades have confirmed the existence of the polar wind. These observations spanned the altitude range from 1000 to similar to 50,500 km, and revealed several important features in the polar wind that are unexpected from '' classical '' polar wind theories. These include the day-night asymmetry in polar wind velocity, which is 1.5-2.0 times larger on the dayside; appreciable O+ flow at high altitudes, where the velocity at 5000-10,000km is of 1-4km/s; and significant electron temperature anisotropy in the sunlit polar wind, in which the upward-to-downward electron temperature ratio is 1.5-2. These features are attributable to a number of '' non-classical '' polar wind ion acceleration mechanisms resulting from strong ionospheric convection, enhanced electron and ion temperatures, and escaping atmospheric photoelectrons. The observed polar wind has an averaged ion temperature of similar to 0.2-0.3eV, and a rate of ion velocity increase with altitude that correlates strongly with electron temperature and is greatest at low altitudes (< 4000 km for H+). The rate of velocity increase below 4000 km is larger at solar minimum than at solar maximum. Above 4000 km, the reverse is the case. This suggests that the dominant polar wind ion acceleration process may be different at low and high altitudes, respectively. At a given altitude, the polar wind velocity is highly variable, and is on average largest for H+ and smallest for O+. Near solar maximum, H+, He+, and O+ ions typically reach a velocity of 1 km/s near 2000, 3000, and 6000 km, respectively, and velocities of 12, 7, and 4 km/s, respectively, at 10,000km altitude. Near solar minimum, the velocity of all three species is smaller at high altitudes. Observationally it is not always possible to unambiguously separate an energized '' non-polar-wind '' ion such as a low-energy '' cleft ion fountain '' ion that has convected into a polar wind flux tube from an energized '' polar-wind '' ion that is accelerated locally by '' non-classical '' polar-wind ion acceleration mechanisms. Significant questions remain on the relative contribution between the cleft ion fountain, auroral bulk upflow, and the topside polar-cap ionosphere to the O+ polar wind population at high altitudes, the effect of positive spacecraft charging on the lowest-energy component of the H+ polar wind population, and the relative importance of the various classical and non-classical ion acceleration mechanisms. These questions pose several challenges in future polar wind observations: These include measurement of the lowest-energy component in the presence of positive spacecraft potential, definitive determination and if possible active control of the spacecraft potential, definitive discrimination between polar wind and other inter-mixed thermal ion populations, measurement of the three-dimensional ion drift velocity vector and the parallel and perpendicular ion temperatures or the detailed three-dimensional velocity distribution function, and resolution of He+ and other minor ion species in the polar wind populatin. (C) 2007 Elsevier Ltd. All rights reserved.

The Venus Climate Orbiter mission (PLANET-C), one of the future planetary missions of Japan, aims at understanding the atmospheric circulation of Venus. Meteorological information will be obtained by globally mapping clouds and minor constituents successively with four cameras at ultraviolet and infrared wavelengths, detecting lightning with a high-speed imager, and observing the vertical structure of the atmosphere with radio science technique. The equatorial elongated orbit with westward revolution fits the observation of the movement and temporal variation of the atmosphere which as a whole rotates westward. The systematic, continuous imaging observations will provide us with an unprecedented large data set of the Venusian atmospheric dynamics. Additional targets of the mission are the exploration of the ground surface and the observation of zodiacal light. The mission will complement the ESA's Venus Express, which also explores the Venusian environment with different approaches. (C) 2007 Elsevier Ltd. All rights reserved.