Wataru Miyake

Telescope of extreme ultraviolet (TEX) onboard SELENE: science from the Moon

The Upper Atmosphere and Plasma Imager (UPI) is to be launched in 2007 and sent to the Moon. From the lunar orbit, two telescopes are to be directed towards the Earth. The Moon has no atmosphere, which results in there being no active emission near the spacecraft; consequently, we will have a high-quality image of the near-Earth environment. As the Moon orbits the Earth once a month, the Earth will also be observed from many different directions. This is called a “science from the Moon”. The two telescopes are mounted on a two-axis gimbal system, the Telescope of Extreme ultraviolet (TEX) and Telescope of Visible light (TVIS). TEX detects the O II (83.4 nm) and He II (30.4 nm) emissions scattered by ionized oxygen and helium, respectively. The targets of extreme-ultraviolet (EUV) imaging are the polar ionosphere, the polar wind, and the plasmasphere and inner magnetosphere. The maximum spatial and time resolutions are 0.09 Re and 1 min, respectively.

Feasibility study of the O II 83.4-mm imaging of the inosphere and magnetosphere

Recent in-situ plasma observations find that large amounts of O+ are escaping from the terrestrial ionosphere to the magnetosphere. Remote-sensing methods using the extreme ultraviolet (EUV) emission of O+ have been expected to be a powerful tool to provide a global perspective on the escaping processes. The overall picture is also very important for the practical use such as monitoring space weather. O+ ions resonantly scatter the solar photons with wavelength 83.4 nm. The key to the success of the observation is to prevent from detecting the H Ly-α line (121.6 nm), which is stronger than the predicted O 11 emission by four orders of magnitude. We have successfully detected O II emission from the uppermost part of the ionosphere using the sounding rocket SS-520-2 to investigate heavy ion escape from the. cusp/cleft region. This success demonstrates the capability of the remote-sensing method to take an instantaneous 2-dimensional image of the O+ distribution, and provides a way for optical observation of the magnetosphere. We plan to obtain O II images of the polar wind using the Telescope for EXtreme ultraviolet light, which is an upgrade version of the instrument for the sounding rocket, in the Upper atmosphere and Plasma Imager component (UPI-TEX) on the SELenological and ENgineering Explorer (SELENE). We refer to the feasibility of the O 11 imagery from the lunar orbit satellite.

Soft ion precipitation at very high latitudes during northward interplanetary magnetic field

During extended periods of northward interplanetary magnetic field (IMF), soft ion precipitation was frequently observed at very high latitudes (>80° ILAT) on EXOS D (Akebono). The precipitating protons typically had temperatures of a few hundreds of eV, and were accompanied by precipitating electrons with temperatures of several tens of eV. The densities of the precipitating protons were of the order of 10−1 cm−3, and were usually lower than those of the electrons. During these periods, the ion convection at the highest latitudes was chaotic or weak, but often had an average antisunward component. During periods of strongly northward IMF, ion precipitation was observed at all magnetic local times (MLT). A flux minimum, sometimes below the level of detection of the Akebono suprathermal mass spectrometer instrument, was often found just poleward of the dayside auroral oval. This region is believed to coincide with the open magnetic field lines in the tail lobe. The region of ion precipitation was observed at auroral latitudes on the dawnside when the IMF By changed polarity from negative to positive; it was located at higher latitudes (>80° ILAT) on the duskside when the IMF By was positive. These observations suggest a connection between the ion precipitation and the auroral oval.

Stream interaction as a heat source in the solar wind

Proton heating at stream interaction regions in the solar wind is investigated based on the solar wind data obtained by Suisei spacecraft between 0.68 and 1.01 AU from the Sun. The deflection angle of the solar wind flow in the ecliptic plane is used to identify the interaction region. In the solar wind flows coming from east of the Sun in low-speed streams and coming from west in high-speed streams, the radial gradient of proton temperature is flattened owing to heating in the interaction region. From comparison of the best-fitted power law dependence of proton temperature on the radial distance in the deflected flow with that in the non-deflected flow, it is suggested that heating in the interaction regions starts around 0.6–0.7 AU from the Sun.

Relationship between low-frequency electric-field fluctuations and ion conics around the cusp/cleft region

We investigated the relationship between low- frequency (0.2-4.0 Hz) electric-field fluctuations (LEFs) and ion conics around the dayside cusp/cleft region in the alti- tude range from 5000 to 100 00 km from observations made by the Akebono satellite. Ion conics were generally associ- ated with intense LEFs. We found a significant correlation between the power spectral density of LEFs at any frequency and the energy of simultaneously observed ion conics. Ion conics with a conic angle near 90 deg and those more aligned with magnetic field lines both had an equivalent correlation with the local intensity of the LEFs. The LEFs associated with near-perpendicular ion conics were, however, generally more intense than those associated with folded conics. The difference was clearer for low-energy conics. These results are in agreement with a scenario of height-integrated heating of ions and energization of ions by electromagnetic energy supplied by local LEFs. Ions generally stay in the energiza- tion region during their upward motion along the field line, so that more folded ion conics with weak energization reach the same energy level as near-perpendicular conics with strong energization, due to the difference in integration time. The limit on residence time in the intense heating region causes the clearer difference for low-energy conics. We set up a simple model to examine the relationship between the ener- gization rate and the evolution of ion conics along the field lines, and obtained good agreement with the observation re- sults.

Energization of Ionospheric Ions around the Cusp/Cleft Region:—A Short Summary of Recent Akebono Results—

We seek a possibility of low‐frequency (0.2–4.0 Hz) electric‐field fluctuations (LEFs) as a possible energy source of transverse ion heating around the cusp/cleft region. Intense LEFs and transversely heated ions (ion conics) have an occurrence peak at the prenoon region. They both have a similar dependence on high‐speed solar wind streams, interplanetary magnetic field components By and Bz. We also found a significant correlation between the power spectral density of LEFs and the energy of simultaneously observed ion conics. Ion conics with a conic angle near 90 degrees and those more aligned with magnetic field lines both had an equivalent correlation with the local intensity of the LEFs. LEFs associated with near‐perpendicular ion conics were, however, generally more intense than those associated with folded conics. The difference was clearer for low‐energy conics. These results are in agreement with a scenario of height‐integrated heating of ions and energization of ions by electromagnetic energy supp...

Space Weather Mission of SmartSat Program

The SmartSat Program is a collaborative program of government agency (NICT,JAXA) and private sector (MHI) in Japan to develop small satellite about 200 Kg. The space weather experiment of the SmartSat consists of Wide Field CME Imager (WCI), Space Environment Data Acquisition Equipment (SEDA), and mission processor (MP). Both of the instruments will be principal components of the L5 mission. WCI is a imager to track CME as far as earth orbit. CME brightness near earth orbit is expected 1E‐15 solar brightness or 1/200 of zodiacal light brightness. To observe such a extreme faint target, we are developing wide field of view camera with very high sensitivity and large dynamic range. These highly challenging experiment and demonstration will be implemented in SmartSat program.