The 46.5-MHz MU (middle and upper atmosphere) radar is a very unique radar capable of measuring the lower atmosphere and the ionosphere with an active phased-array system. The newly implemented capabilities and antenna pattern calibrations of this radar were given [Fukao et al., 1990]. An HF coherent radar experiment for exploring the Antarctic high-latitude ionosphere was proposed [Ogawa et al., 1990]. The experiment will start in early 1995. A plan of constructing an incoherent scatter radar at Spitsbergen was presented [Matuura and Oguti, 1991]. This radar aims at snap-shot observations of the transient structure and dynamics in the dayside cusp or polar cap ionosphere with time resolution less than a minute.
A METS (microwave energy transmission in space) experiemnt was proposed [Matsumoto et al., 1990]. Two fundamental areas are addressed: one is the development of a control system for the microwave beam; the other concerns the study of nonlinear propagation effects of the beam as it passes through space plasmas. Computer experiments using a two-dimensional electromagnetic particle code were made to study the nonlinear plasma dynamics associated with electrodynamic tether system [Usui et al., 1991, 1993].
Spatial pattern and movement of the 30-MHz cosmic noise absorptions were observed by a two-dimensional multi-beam (8x8 beams) riometer in the northern polar cap [Nishino et al., 1990]. A method of analysis for the monochromatic aurora stereo TV observations was examined [Aso et al., 1990]. In this method, first, a camera model is obtained by using calibration data for the background stars, and then, an inverse problem is solved which reconstructs three-dimensional luminosity structures of photoemission from two-dimensional auroral images. This method was applied for the stereoscopic observation of a stable auroral arc. A new type of auroral imaging spectrometer was developed [Okamura and Ejiri, 1992]. This can measure spectral apparent emission rate of aurora in coordinates of wavelength and spatial field of view of 72.6 degrees with a maxium time resolution of 0.2 s.
A balloon observation of auroral X-rays was carried out in Norway by using X-ray imagers [Yamagami et al., 1990]. The X-ray images were obtained by a two-dimensional 5x5 matrix array of Si(Li) semiconductor detectors with 3-s time intervals. Feasibility studies of the long-term circumpolar balloon experiment, called the Polar Patrol Balloon (PPB) project, aiming at establishing a station network in the stratosphere over the Antarctica for geophysical and astrophysical observations were reported [Hirasawa et al., 1990; Ejiri et al.,1993]. Three test flights in 1987 and 1990 at Syowa Station convinced us that PPB would come back to the launching site. The PPBs carrying auroral X-ray, electric and magnetic field detectors were launched during 1991-1993.
Aso,T., T.Hashimoto, M.Abe, T.Ono and M.Ejiri, On the analysis of aurora stereo observation, J. Geomag. Geoelectr., 42, 579-595 (1990)
Ejiri,M., A.Kadokura, T.Hirasawa, N.Sato, R.Fujii, H.Miyaoka, J.Nishimura, N.Yajima, T.Yamagami, S.Kokubun, H.Fukunishi, M.Yamanaka and M.Kodama, Polar patrol balloon experiment in Antarctica, Adv. Space Res., 13, (2)127-(2)130 (1993)
Fukao,S., T.Sato, T.Tsuda, M.Yamamoto, M.D.Yamanaka and S.Kato, MU radar: New capabilities and system calibrations, Radio Sci., 25, 477-485 (1990)
Hirasawa,T., M.Ejiri, N.Sato, R.Fujii, H.Miyaoka, A.Kadokura, J.Nishimura, N.Yajima, T.Yamagami, S.Kokubun, H.Fukunishi, M.Yamanaka and M.Kodama, Polar patrol balloon experiment during 1991-1993, Proc. Internat. Symp. on Space Technology and Science, ISAS, Tokyo, 1593-1597 (1990)
Igi,S., H.Minakoshi and M.Yoshida, Automatic ionogram processing system 2. Automatic ionogram scaling, J. Commun. Res. Lab., 39, 367-379 (1992)
Igi,S., Automatic ionogram processing system 3. A new method of displaying ionospheric characteristics, J. Commun. Res. Lab., 39, 381-402 (1992)
Matsumoto,H., N.Kaya and M.Nagatomo, Microwave energy transmission experiment, Space Power, 9, 113-130 (1990)
Matuura,N. and T.Oguti, Japanese plans for Spitsbergen radar, Annal. Geophys., 9, 339 (1991)
Nishino,M., Y.Tanaka, T.Oguti and A.Egeland, CNA observations by a multibeam riometer at Ny-Alesund in the polar cap, Eos Trans. AGU, 71, 912 (1990)
Nozaki,K., N.Nagayama and H.Kato, Automatic ionogram processing system 1. Data reduction and transmission of ionogram, J. Commun. Res. Lab., 39, 357-365 (1992)
Ogawa,T., T.Hirasawa, M.Ejiri, N.Sato, H.Yamagishi, R.Fujii and K.Igarashi, HF radar experiment at Syowa Station for the study of high-latitude ionosphere - 2 : A capability, Proc. NIPR Symp. Upper Atmos. Phys., 3, 91-95 (1990)
Okamura,H. and M.Ejiri, A new imaging spectrometer for the auroral spectroscopic studies, J. Geomag. Geoelectr., 44, 193-205 (1992)
Usui,H., H.Matsumoto and Y.Omura, Electron beam injection and associated LHR wave excitation: Computer experiments of (SHUTTLE) electrodynamic tether system, Geophys. Res. Lett., 18, 821-824 (1991)
Usui,H., H.Matsumoto and Y.Omura, Plasma response to high potential satellite in electrodynamic tether system, J. Geophys. Res., 98, 1531-1544 (1993)
Yamagami,T., H.Miyaoka, A.Nakamoto, Y.Hirasima, S.Ohta, M.Namiki, H.Murakami, N.Sato, R.Fujii, K.Okudaira, J.Nishimura and M.Kodama, Two-dimensional auroral X-ray image observation at a balloon altitude in the northern auroral zone, J. Geomag. Geoelectr., 42, 1175-1191 (1990)
A remarkable increase in the height of maximum electron density with duration of about two hours was observed with the MU radar experiments made around midnight on January 20-21, 1989, and it has been suggested that the disturbance was caused by unusually large eastward electric field at mid-latitudes associated with the onset of a substorm in the polar region [Reddy et al., 1990; Reddy et al., 1991]. Studies on spatial and temporal variations in the F-region electron density profiles during disturbed periods were made by four-beam measurements with the MU radar, and it has been found that ionospheric disturbances travel in the direction predominantly equatorward during the disturbed conditions [Takami et al., 1991]. With the four-beam experiments carried out during the geomagnetic storm of 20-23 October 1989, when the auroral display was seen in Japan, a strongly structured ionosphere with large spatial gradients in the electron density profiles was observed to stream over the radar site [Oliver et al., 1991b]. The F-region ionospheric disturbances during the two events of auroral display seen in Japan on 21 October and 17 November, 1989, were investigated with the ionograms obtained from the chain of Japanese ionosondes, and it has been suggested that the ionospheric disturbances generated at around 60deg N in the north of Japan traveled over the chain [Igarashi et al., 1991].
The ionospheric disturbances over Japan asssociated with the geomagnetic storm during the period from 30 November to 1 December, 1988, were studied with various kind of ground-based radio techniques and theoretical point of views; Digisonde and routine ionosonde network [Igi et al., 1992], oblique ionospheric-sounding network [Igarashi and Takeuchi, 1992], HF signals Doppler detector network [Kainuma et al., 1992], TEC experiments with ETS-II 136 MHz beacon [Minakoshi et al., 1992], ionospheric scintillation measurements with ETS-II, BS-2(12 GHz) and CS-3(20 GHz) [Nishimuta et al., 1992], and with six NNSS satellites(150 MHz and 400 MHz) [Ogawa et al.,1992b], penetration of electric field from the magnetosphere [Tanaka, 1992] and generation of ionospheric irregularities by ExB drift instability [Maruyama and Okamoto, 1992].
Intense coherent echoes from the field-aligned F-region irregularities were observed with the MU radar and motions of the irregularities, particularly turbulent upward (northward) and downward (southward) motions inside the irregular patches were detected [Fukao et al., 1991b]. Possible mechanisms for the events were discussed in terms of the influences of gravity waves, ExB instability and turbulent cascade process [Kelley and Fukao, 1991]. Macroscopic instability, or the growth rate of instability, in the nocturnal ionospheric F-region at mid-latitudes under the influences of an external eastward electric field was examined allowing for the ionospheric ion composition as a mixture of oxygen and hydrogen ions [Maruyama, 1990].
The daytime horizontal phase velocities of medium-scale traveling ionospheric disturbances observed with Japanese HF Doppler receiver network were discussed in the light of atmospheric gravity wave theory [Shibata and Okuzawa, 1991]. HF Doppler measurements coordinated with infrasonic wave measurements were made at Fairbanks, Alaska, and it was found that some of the ionospheric disturbances seen on the HF Doppler data indicated a correlation with enhancement of infrasonic waves detected on the ground [Minami et al., 1991].
The geomagnetic field variation and current system simulated by an asymmetrical ionospheric dynamo model for a solstitial condition allowing for generation of interhemispherical field-aligned currents were compared with the observed features of the soltitial Sq system [Takeda, 1990]. Effects of the Hall conductivity upon the ionospheric dynamo were examined and it has been suggested that its effects appear as enhancement of the intensity of the equivalent current by 2.1 times rather than as modification of the global current pattern [Takeda, 1991]. It has been pointed out that some parts of strom-time geomagnetic field variations at mid-latitude stations were caused directly by the magnetospheric field-aligned currents connected to the partial ring current system and controlled by IMF-By [Iyemori, 1990]. The electrical coupling between the high-, middle-, and low-latitude ionospheres were examined during GISMOS campaign in January 1984, using interplanetary and high-latitude magnetic field data together with F-region plasma drift measurements with incoherent scatter radars and it has been shown that the meridional electric field perturbations were considerably more attenuated with decreasing latitude than the zonal fluctuations [Fejer et al., 1990]. The interaction of a plane HM wave propagated earthward from the noon magnetopause within the equatorial plane of the magnetosphere was examined theoretically and the results were compared with characteristics of geomagnetic sudden commencements [Ohnishi and Araki, 1992].
Optical measurements of the aurorae, seen at the extremely low latitude region as Japan during the severe geomagnetic storm on Ocober 21, 1989, were made with the airglow spectrograph at Niigata (33.7deg N, 138.8deg E) [Saito et al.,1991; Takahashi et al., 1991] and enhancements in [OI] 630.0nm and 636.4nm doublet and [OI] 557.7nm, with intensities of 6.7 KR, 2.0 KR and 1.4 KR, repectively at the zenith were observed. An apparent lifetime of the auroral red line 630.0nm emission was investigated using monochromatic auroral TV images observed at Syowa, Antarctica to evaluate mean energy of the impinging electrons [Ono and Hirasawa, 1992]. An auroral TV camera was installed on the satellite Akebono (EXOS-D) for studies of auroral dynamics and for monitoring of magnetospheric activities and preliminary results were presented [Oguti et al.,1990]. Correlated enhancements of bremsstrahlung X-rays and VLF emissions in quasi-periodic manner were observed at balloon altitude over Syowa, Antarctica [Suzuki et al., 1992]. Occurrences of pulsative variations in the cosmic radio noise absorption (CNA) associated with the storm sudden commencements (SSC) were investigated from the data obtained at Syowa, Antarctica, and it has been shown that the occurrence rate was highest in the morning with a secondary peak before midnight [Nagano et al., 1991]. Quasi-periodic variations in CNA were observed at Syowa, Antarctica and at the magnetically conjugate station Husafell in Iceland and movements of CNA sources were discussed [Shibuya et al., 1991].
Observations of the mass/energy/angle distributions of the thermal (0-25eV) and the suprathermal(25eV-several KeV) ions in the lower magnetosphere were made with the Suprathermal Ion Mass Spectrometer (SMS) on EXOS-D satellite [Whalen et al.,1990], and it has been found that ions other than H+, notably O+, He+, O++, N+ and N++, constituted a significant component of the thermal ion population in the high-altitude polar ionosphere [Yau et al., 1991] and also that two events of low-energy upflowing ions revealed different two types of the ion angle distribution, one predominates with conical ion pitch angle distribution and the other with field-aligned distribution [Sagawa et al., 1991]. Observations of the upflowing ions were also made with the Low Energy Particle (LEP) instrument for measurements of energy and pitch angle distributions of auroral electrons (10eV-16KeV) and ions (13eV-20KeV) and with the Ion Mass Spectrometer (IMS) for measurements of ion species (300eV-25KeV) onboard EXOS-D. From measurements with LEP, a good correlation between the field aligned bulk shift of upflowing ions with energies up to 100 eV and electron precipitations was found [Miyake et al., 1991]. Measurements with IMS instrument on EXOS-D indicated existence of upflowing ions with both field-aligned and conical pitch angle distributions [Kaya et al., 1990].
Measurements of particle fluxes in the polar cusp region made with LEP instrument on EXOS-D revealed intense but patchy electron fluxes accompanied by KeV-range ions which were interpreted as signatures of the magnetosheath plasma injection [Mukai et al., 1990] and also revealed energy dispersions of three different types for the injected solar wind ions [Mukai et al., 1991]. High-frequency (>0.5 Hz) oscillations in electric fields associated with the precipitation of magnetosheath plasma, i.e., ions with energies of 0.1 to 1KeV and electrons above 100eV, were observed with EXOS-D at the polar cusp, and it has been suggested that the high-frequency turbulence in the polar cusp was due to Alfven waves propagated from the magnetopause [Matsuoka et al., 1991]. Transpolar auroras, their associated particle precipitation, and their occurrence with respect to the IMF By polarity were examined using auroral images and particle data from DMSP F6 satellite and it has been suggested that transpolar arcs, the so called theta aurora, were located along the poleward boundary of the extended precipitation region from the oval, or of the closed field line region, and controlled by the polarity of the IMF By [Makita et al., 1991]. Data from LEP on EXOS-D were examined over 30 dawn to dusk passes to identify the polar cap boundary during the northward IMF condition and it has been found that the data for electron precipitation alone were not suitable to identify the polar cap boudary but the data for ions indicated well defined boundaries not exceeding the invariant latitude of 82 degrees [Obara et al., 1992]. Relationships between particle precipitation within the dusk-to-midnight sector and substorm activity were examined using particle and auroral image data from DMSP as well as ground-based magnetograms and it has been suggested that energization of the particles took place in the near tail region associated with substorm onset [Nakamura and Yamamoto, 1992].
The temperature of thermal electrons in connection with the field-aligned currents (FACs) in the auroral region were examined using data from the Thermal Electron Detector (TED) and the Fluxgate Magnetometer (MGF) on EXOS-D, and it has been found that electron temperatures were higher and lower respectively in the region of upward and downward FAC than that in the neighboring non-FAC region [Abe etal.,1991]. Measurements of FACs were made with MGF on EXOS-D, and intense small-scale FACs embedded in the large-scale FAC system and the region 0 currents flowing in the poleward region adjacent to the region 1 currents were found at 1-2 Re altitudes [Fukunishi et al., 1990]. Further, it has been found that small-scale FACs in the form of current sheet structure with the width of 5-20km always existed within the large-scale region 1, region 2, cusp and polar cap current systems and had one-to-one correspondence with localized precipitations of electrons with energy range from 10eV to several KeV [Fukunishi et al., 1991]. The equatorward cutoffs of ion and electron precipitation in relation to the evening region 2 FAC were examined for isolated substorms using the magnetic field and plasma data from the DE-2 satellite and it has been found that the equatorward boundary of the region 2 current coincided well with that of 10-20KeV ion precipitation during the whole course of substorms [Fujii et al.,1990]. Characteristics of FACs in the evening and morning regions during the great magnetic storm on March 13-14, 1989, were investigated using magnetic and electric field data from EXOS-D, and it has been found that the equatorward boundary of the FAC region began to move equatorward right after the SSC, but the poleward boundary of the FAC region did not respond to the SSC, and further that with development of the storm the FAC system extended equatorwards and changed into complicated patters consisting of multiple pairs of upward and downward FACs [Fujii et al., 1992]. Structures of FACs and plasma convection in the midnight auroral region during stable northward IMF (Bz>0) condition were examined using data from Magsat and DE-2, and it has been found that triple-sheet of FACs under control of IMF By developed at higher latitude than the usual region-1 and -2 FAC system [Taguchi, 1992], and also that convection patterns well corresponded to the triple-sheet FACs [Taguchi et al., 1992a]. From analyses of DE-2 data, it has been found that a pair of FACs dveloped at the polar cusp region poleward of the usual region-1 and -2 FAC system under control of intensity and direction of IMF By [Taguchi et al., 1992b]. The ratio of the magnetic to electric field components of the perturbations perpendicular to the magnetic field line in the high latitude FAC region was examined using tha data from the DE-2 satellite, and it has been found that the values of the ratio changed from a constant value (corresponding to the height-integrated Pedersen conductivity) for perturabations with longer period than about 8s to the another constant (inverse proportional to Alfven velocity) for perturbations with shorter period than 4s [Ishii, et al., 1992]. Computer study on the generation of FACs from a current sheet was made based on three-dimensional fast reconnection model [Ugai, 1992].
Simultaneous increase in the flux of electrons with energies of 30-200 Kev at geosynchronous orbit with the onset of activities in Pc5 magnetic pulsation and riometer (cosmic radio noise) absorption was observed [Saka et al., 1992]. Measurements of electric field were made with the Elecric Field Detector (EFD) on EXOS-D, and an intense electric field was observed at the region between the region 1 and region 2 currents in the morning sector and fluctuating electric fields were observed at the polar cusp [Hayakawa et al., 1990]. Acceleration processes for electrons due to field-aligned electric field were discussed based on particle and magnetic field data from the rockets launched into auroral arcs over Syowa Station, Antactica [Shiokawa et al., 1990] and also based on particle and aurora image data from the DMSP-6 and -7 satellites [Shiokawa and Fukunishi,1991]. Field-aligned electric field acceleration of trapped elctrons resulting them to precipitate into the upper atmosphere was discussed theoretically and the result was compared with the auroral X-ray data [Hirasima, 1991].
The cross-polar cap potential difference estimated from ground magnetic data combined with an empirical ionospheric conductivity distributions estimated from DMSP X-ray image data, was compared with the AE index and a significant correlation between the potential difference and the AE index was found [Ahn et al., 1992]. Analyses of several global measures of high-latitude ionospheric electrodynamic activity were made on the basis of results obtained from a mapping procedure for the ionosphere electrodynamics applied to incoherent scatter radar and ground magnetometer observations for two-day period of 18-19 January 1984 [Richmond et al., 1990]. Instantaneous patterns of electric fields and currents in the high-latitude ionosphere were estimated from the combined data of drift velocity measurements with satellite and radar, along with ground-based magnetometer observations for the period of a relatively stable southward IMF on 25 October 1981, and it has been shown that a pair of the potential cells associated with the substorm expansion coexisted at the nightside sector in addition to the usual pair of convection cells [Kamide and Richmond, 1991]. It has been demonstrated that ionospheric conductivities and electric field played different roles in controlling the strength of the auroral electrojets at different latitudes and local times and that there were two essentially different coexisting current systems throughout a substorm, one was controlled by the electric field and the other by the ionospheric conductivity [Kamide, 1991]. An attempt was made to unify results from observations of electrodynamic phenomena, especially plasma convection patterns, in the polar cap, on the basis of types of the interaction between the terrestrial and interplanetary magnetic fields [kamide and Troshichev, 1992].
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The ELF/VLF emission data obtained by GEOS 1 satellite revealed the existence of wavelets, or monochromatic wave components, in the hiss band which were closely related to triggering of chorus emissions [Hattori et al., 1991a; 1991c; 1992]. Long term variations of ELF/VLF emissions were examined with data from Syowa in Antarctica and Husafell in Iceland. The result shows strong diurnal and seasonal variations controlled by sunlight conditions and a control of geomagnetic activity [Sato et al.,1990; 1991]. The occurence distribution of electrostatic ion cyclotron emissions were obtained by analyzing ELF/VLF data from many satellites [Yoshino,1991]. The wave mode of electrostatic noises observed by ISEE 3 in the ELF/VLF range was identified as the ion acoustic wave from the dispersion relation [Tsutsui et al., 1991].
Statistical characteristics of whistler-triggered VLF emissions were obtained by analyzing 10 year data from Moshiri, including diurnal, seasonal variations, Kp-dependence of occurrence frequency, and the existence of two L shells with high occurrence frequency [Hayakawa, 1991]. The L-dependence of whistler-triggered emissions were further confirmed by observations at Ceduna, Australia [Hayakawa and Ohta, 1992]. Theoretical and numerical studies of VLF triggered emissions generated by man-made signals were reviewed with emphasis on the future capabilities of numerical simulations in nonlinear physics [Omura et al., 1991]. The satisfactory performance of VLF instruments on board Akebono (EXOS-D) was proved by preliminary observations [Kimura et al., 1990]. Effects of the plasmapause on whistler mode wave propagation were investigated by means of ray-tracings for a wide frequency range relevant to studies of various kinds of VLF/ELF emissions [Hattori et al., 1991b].
Measurements of whistler-mode waves of Decca navigation signals near Birdsville, Australia revealed ducted propagation of LF whistler-mode signals and the intensity increase and the frequency shift related to magnetospheric electric fields and storm-related energetic electrons [Tanaka and Nishino, 1991].
During a geomagnetic storm, unusual increases of field strength of 2.5 and 5 MHz JJY signals were observed at Akita, and VHF-TV signals (56.5 MHz) from China were received at Tokyo. Both were found to be caused by unusual increase of foF2 during the storm [Ichinose and Kamata, 1992].
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Yoshino,T., On the distribution of polar electrostatic emissions and their relationships to auroral hiss and direction finding measurements of saucer emission in the polar regions observed by ISIS, KYOKKO and AKEBONO satellites, Adv. Space Res., 11 (9), 45-50 (1991)
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