A full-disk solar magnetograph was constructed at the Mitaka campus of the National Astronomical Observatory of Japan, in support of the STEP project. The basic principle of magnetic field measurement and the configuration of the instrument are presented.

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The outine of a new solar Flare-Monitoring-Telescope is given, which was built at the Hida Observatory of Faculty of Science, Kyoto University, in the first financial year of the Japan's STEP project. The telescope is unique among currently-operating solar flare-patrol-telescopes, because it can simultaneously observe five solar images, which are four full disc images in Hα center, Hα + 0.8 Å, Hα - 0.8 Å and continuum, and one solar limb image in Hα center. After its start of operation it was confirmed that this telescope system is very useful to study the dynamical features of Hα filament disappearance, because it can, for the first time, continuously record the full solar disc simultaneously in three wavelengths of the Hα line. Two typical examples of Hα filament disappearance observed with the telescope are demonstrated and are comparatively studied. It is found that the more dynamical and more energetic Hα filament eruption causes the larger enhancement of soft X-ray bright arcade structure observed with the Soft X-ray Telscope of Yohkoh.

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The Yohkoh spacecraft observed a large flare (Ha importance 3B and GOES (Geosynchronous Operational Environmental Satellite) class X6.1) on 27 October 1991. The flare showed strong gamma-ray emission above 1 MeV. The gamma-ray spectrum, which extends to 10 MeV/nuc, consists of electron bremsstrahlung continuum and several gamma-ray lines. The gamma-ray observation indicates that electrons and protons were accelerated to >1 MeV and >10 MeV, respectively, during the maximum phase of the flare. Assuming second-order Fermi stochastic acceleration, we derive the Bessel function-type proton spectrum of αT = 0.029 from a ratio of neutron capture line to nuclear deexcitation line fluences and estimate several parameters describing the acceleration process. In a case of first-order Fermi shock acceleration, the proton spectrum can not be derived from the gamma-my lines. If the shock compression ratio (ratio of upstream to downstream bulk plasma flow velocities) and the spectral characteristic energy are taken to be 1.8 and 100 MeV, respectively, the shock acceleration gives the proton spectrum similar to that obtained from second-order Fermi stochastic acceleration. It is not possible to determine the acceleration mechanism from the gamma-ray lines alone. Moreover, the Yohkoh hard X-ray spectrometer observed ⁷Be (429 keV) and ⁷Li (478 keV) lines resulting from ⁴He+ ⁴He reactions from two flares on 27 October 1991 and 15 November 1991 (H_α importance 3B and GOES class X1.0). From the ⁷Be and ⁷Li line profiles we suggest that the angular distribution of accelerated alpha particles (⁴He nuclei) is peaked in a direction tangential to the photosphere for the 27 October flare, whereas it is peaked in the downward direction for the 15 November flare.

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Many coronal holes have been observed by the Yohkoh Soft X-ray Telescope (SXT). These holes appear as dark regions in the soft X-ray images. It is now widely accepted that coronal holes are sources of high-speed solar wind. However, the size of coronal holes has not been clearly defined in previous works, and the relationship between soft X-ray coronal holes and high-speed solar wind is still not fully understood. In this paper we check the results from Skylab observations against the Yohkoh SXT data. We examined the boundaries of soft X-ray coronal holes imaged by the SXT. We then analyzed the characteristics of coronal holes associated with high-speed solar wind at 1 AU and compared the results with Skylab data. Faster solar wind seems to blow from larger and darker coronal holes. Coronal holes at relatively high latitudes (more than 30°), which extend from polar coronal holes, also produce high-speed streams, as coronal holes located around the solar equator. The manifestation of coronal holes and the sudden changes in their boundaries are frequently associated with large-scale coronal disturbances (LCDs) such as filament eruptions or flares. LCDs maybe a possible source of non-recurrent interplanetary disturbances, and transient holes suggest the formation of open magnetic fields related to these events.

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A new solar neutron detector has been designed and has been set at Mt. Norikura Cosmic Ray Observatory since October 1990. The detector has successfully detected solar neutrons associated with large solar flares of June 4th and 6th 1991. Solar neutrons have been observed also by a traditional neutron monitor and a moon detector. The authors have compared the observed results obtained by the new neutron detector, the neutron monitor and the union detector and the response of each detector to solar neutrons has been discussed.

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A scintillator muon telescope was installed at the Hobart Campus of the University of Tasmania (42.85°S, 147.42°E), Australia in December 1991. It is part of a North-South Network of Multi-Directional Cosmic Ray Muon Surface Telescopes, in conjunction with the Nagoya Cosmic Ray Muon Telescope (35.12°N, 136.97°E). Using two years of data from the North-South Network, we have investigated the average features of the solar diurnal and semi-diurnal variations. Preliminary results of the analysis show that two years averages of the observed diurnal variations are composed of a north-south symmetric and an asymmetric variations. The north-south asymmetric diurnal variation is consistent with that expected from the semi-diurnal anisotropy which produces the observed semi-diurnal variation. It is shown that the reference axis of the anisotropy is in the direction of about 7°S sunward from the ecliptic.

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Cross-correlation analyses between galactic cosmic-ray intensities from Calgary neutron monitor and several solar-activity parameters, on daily basis, have been undertaken. We report here results connected with the unresolved full-solar X-Ray background and the occurrence of solar LDE-type flares (both from GOES-satellite data) in the time interval July 1988-June 1989 (i.e. the last part of the ascending phase of sunspot cycle 22). Our findings do not support the hypothesis that LDE-type flare occurrence is the best parameter to describe the medium-term modulation of galactic cosmic rays; however, it could be a good indicator of sudden but stable coronal variations occurring along the solar-activity cycle, i.e. a proxy data set to include peculiar transient-induced effects on the long-term cosmic-ray modulation studies.

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Power spectra and fractal dimensions have been determined for cosmic ray data obtained from the Mt. Norikura air shower experiment between 1972 and 1987, and from the Matsushiro underground station (220 m.w.e) for the years 1985-1991. The power law indices for Matsushiro and Mt. Norikura are found to be similar to each other, and it is confirmed that these values (∼1.0) are low compared to those (∼5/3) for neutron monitors and for muon telescopes at shallower underground stations. The power spectrum of the Matsushiro data breaks at about 2.5 μHz, corresponding to a period of about five days. These results may give information on magnetic field fluctuations in inter-stellar space in the vicinity of the heliosphere.

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We present the observed results of the cosmic-ray sidereal anisotropy in the primary rigidity range 550-950 GV from the Matsushiro underground (geogr. 36.5°N, 138.0°E; 220 m.w.e. depth) for the period 1984-1994. The moon telescope used is of multi-directional with 17 channels, which scan simultaneously over the median latitude of viewings from-60° N to -15°S on the celestial sphere. We obtain significant sidereal diurnal and semi-diurnal terms in the daily variations with several s.d., being consistent with other observations. Most notably, the north-south asymmetry in the diurnal variations is confirmed without solar modulation, in which the amplitude increases as the direction of viewings of the telescopes moves southward towards and over the equator.

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A new underground moon telescope system installed at a depth of 154 m.w.e. at Liapootah, central Tasmania, has been continuously monitoring cosmic ray intensity since December 1991. In two hemisphere observations, this telescope plays an important roll as a conjugate station to Matsushiro in Japan, which has been operating at a similar depth (220 m.w.e.) since April 1984. In this paper, we analyze data recorded at Liapootah during 33 months from January 1992 to October 1994, to test the north-south asymmetry in the sidereal diurnal variation caused by galactic anisotropy of high energy cosmic ray intensity. W e find average sidereal variation (0.041 ± 0.006%, 3.5 ± 0.6 hr) being observed by the vertical component telescope (median latitude of viewing λE = 36.2°S). Comparison with the sidereal diurnal variation (0.028 ± 0.006%, 2.6 ± 0.8 hr) observed by Matsushiro λE = 34.5°N) during the same period confirms the existence of a north-south asymmetry in which the amplitude of the variation increases as the median direction of viewing moves southward over the equator. This is the first positive result indicating the north-south sidereal asymmetry by two hemisphere observations.

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We describe a multi-station system dedicated to measurements of the solar wind plasma using the interplanetary scintillation technique. The observation system, which is operated at a frequency of 327 MHz, consists of four stations located at Toyokawa, Fuji, Sugadaira and Kiso. The newest station was constructed at Kiso in 1993 to make a four-station system. The present system, however, has insufficient sensitivity to measure enough IPS sources for observing the solar wind with good spatial and temporal resolution. As a result, for example, one synoptic map of solar wind speeds requires the superposition of data for three solar rotations. Therefore we have begun the project to upgrade the antenna system at each station. To start with, the Fuji antenna has successfully been improved with an optimum design of the primary feed system and the development of a low noise preamplifier. The Fuji antenna system after the improvement achieved the minimum detectable flux density of 0.3 Jy (bandwidth: 10 MHz, time constant: 100 ms) which is nearly five times better than the previous system. This upgrade project is expected to be fruitful during the coming decade for solar wind study.

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The single-station measurements of interplanetary scintillation (IPS) at 2 and 8 GHz are used to study the radial distribution of solar wind velocity and density fluctuations near the sun. IPS observations in the ecliptic plane reveal the occurrence of the solar wind acceleration in the radial range between 10 and 30 Rs (solar radii), and also reveal the radial decrease of density fluctuations with a power index of approximately -2. Such structure is basically unchanged during the period from 1990 to 1993; i.e. the solar maximum to the declining phase. On the other hand, IPS observations at the high latitude region of the sun demonstrate a significant reduction of the turbulence level as well as a marked development of high speed streams in the low solar activity. This fact is in good agreement with the well-known solar cycle variation of the coronal hole. From the comparison between IPS data at 2 and 8 GHz, it is found that there is a slight but significant difference in the radial slope of the scintillation index variation. This might be attributed to the effect of either source size or spectral index of turbulence.

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We have quantified the injection rate of low-energy particles (90-1000 keV) at the front of three interplanetary shocks detected by ISEE-3 spacecraft. We have used a MHD code to simulate the shock propagation and the focused-diffusion equation for particle propagation. This allows us to quantify the injection rate of particles, Q, at the shock by fitting the observed flux and anisotropy at different energies. We relate the variations of the efficiency of the particle acceleration with the interplanetary magnetic field and plasma conditions in the shock front region magnetically connected with the observer. Particularly, with the MHD strength of the shock, the interplanetary magnetic field-shock normal angle, the extent of the shock, and the heliolongitude of the parent solar activity that generates the shock.

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We have investigated the solar wind input conditions for geomagnetic storms with Kp greater or equal 8^- during the years 1966-1990 in order to clarify the interplanetary and solar causes of major geomagnetic storms. Forty-one out of the forty-three analyzed storms were found to be caused by transient shock-associated solar wind ejecta (driver gases and magnetic clouds), one storm was caused by a slow moving magnetic cloud followed by a corotating interaction region (CIR) and one by a CIR. Independent of the phase of solar activity coronal mass ejections (CMEs) CMEs are found to be the sources of major geomagnetic storms. A similar result was obtained using the D_st-index as an indicator of major geomagnetic storms. The maximum Kp-values of the individual events were directly related to the peak southward components of the interplanetary magnetic field (IMF). Draping of the IMF near the front edges of driver gases (magnetic clouds) or/and the magnetic field configurations of magnetic clouds were the sources of the extreme negative B_z values. The intensity of the southward components was often substantially amplified at the leading and rear edges of magnetic clouds due to their interaction with the ambient solar wind. This was found to be of particular importance for cases where magnetic clouds were followed by CIRs or interplanetary shocks, especially during very disturbed interplanetary conditions, i.e. during sequences of CMEs.

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We report an observation of the singly-charged oxygen ions (O⁺) in the plasma sheet at X_GSE∼ -60Re. Observed structures in the intensity and angular distribution of O⁺ ions correlated with a localized high-density region and large-scale changes in the proton flow direction. The average energy of O⁺ was much higher than that of the main component (H⁺). The tailward flowing high-density region containing O⁺ ions caused the drastic flow variations in the north-south meridional plane in the plasma sheet. The anisotropic O⁺ distribution probably by finite gyroradius effect was observed just before the density enhancement, while the O⁺ flow direction was the same as that of the proton bulk flow in the high-density region.

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GEOTAIL observation in the distant dusk upstream region showed the existence of the diffuse upstream ions (5-43 keV/q) when the interplanetary magnetic field was nearly radial and separated from the nearest magnetopause by >20-30 RE. Since even with the Bohm limit the perpendicular diffusion was not fast enough to transport the magnetospheric ions to the spacecraft, we conclude that these diffuse ions had a bow shock origin.

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Planning for the OPEN (Origin of Plasmas in the Earth's Neighborhood) program in 1977-1978 was representative of early concepts to obtain a quantitative estimate of the energy flow through the magnetosphere-ionosphere system. The magnetosphere was the focus of those early planning discussions and the OPEN program was defined to address global issues of mass, momentum, and energy flow. The STEP program that we are celebrating at this conference is in many ways a direct evolution of the early work that led to the OPEN program. One of the main characteristics of those early discussions was the desire to obtain a global view of the magnetosphere. This pursuit of a global view not only has persisted through the evolution of OPEN through STEP, but it has been a consistent pursuit of space physics from its very beginnings. In fact, ground-based scientific activities prior to the space age had already recognized the importance of establishing observation networks designed to provide global views of the parameters being observed. In this paper, we review briefly both the early attempts at obtaining a global view of the magnetosphere and the initial arguments for obtaining a global measure of the energy flow through the magnetosphere. We then show, through realistic simulations, what now can be accomplished in the arena of measuring the global energy flow through the magnetosphere and its component parts. We discuss both qualitative and quantitative results, stressing the manner in which global observations play a vital role in furthering our understanding of the magnetosphere and its dynamics. Finally we present an example constructed from a video shown at the symposium that illustrates what might be seen of global magnetosphere dynamics with presently existing instrumentation.

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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 (<20 eV) near the dayside cusp or auroral regions at high altitude (>2000 km) over a latitudinal range less than ∼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° 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.

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The coupling of energy between the solar wind and the magnetosphere has been studied using many different techniques. Early research used simple statistical methods and cross-correlation analyses. Such work suggested that solar wind-magnetosphere coupling is strongly controlled by the interplanetary electric field (-V × B). Later studies have used more sophisticated techniques such as linear prediction filtering to understand quantitatively the time scales and efficiency of such coupling. In fact, there emerge two distinct aspects and time scales for coupling processes: (1) Directly-driven ionospheric dissipation with response time scales of 10-20 min.; and (2) Storage-release mechanisms involving energy loading in the magnetotail for-1 hour. Very recent research has used nonlinear dynamical models and nonlinear filter techniques to incorporate both directly driven and loading-unloading behavior. The result is that very accurate predictions of magnetosphere-ionosphere response are possible using state-input space reconstruction and “nearest neighbor” nonlinear filters.

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A case study of IPDP (Intervals of Pulsations of Diminishing Period) observed in association with low-latitude auroras is reported. Visible red auroras were detected twice in the time intervals of 11h36m-12h30m UT and 14h10m-14h30m UT on October 21, 1989. Simultaneously there were two rapid northward excursions of the H-component magnetic perturbation with the magnitude of more than 150 nT. The IPDP plasma wave events were observed at Yonezawa during the low-latitude auroras. The energy source of the IPDP plasma wave event is inferred to be the wave-particle interaction involving the asymmetric ring current oxygen ions at the bulge region of the plasmapause during the expansive phase of substorms. The frequency increase is explained in terms of a decrease of energy of the oxygen ion stream while the asymmetric ring current decays.

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The main purpose of this paper is to study the temporal evolution of the auroral electrojet indices one hour before and two hours after the instant of the sudden appearance of rayed southern lights (RAD5). We considered the observations of the RADs as the snapshot taken with a single all-sky camera placed at Belgrano Station (78.8°S, 38.8°W). Thirty three events were studied to exemplify the tendency of both electrojet currents to see if they manifest exponential shapes The above mentioned cases were split according to the signature of the AE index around the moment of the observed RADs. We corroborate the relationship between the southward interplanetary magnetic field component and the occurrence of auroral substorms. We confirmed the tendency of the total and the westward electrojet current intensities to increase and decrease according to an exponential time function.

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In order to understand the global magnetospheric responses to solar wind changes and to investigate the transfer (or propagation) processes and latitudinal structures of magnetospheric disturbances, coordinated ground-based observations along the 210° magnetic meridian (MM) are being conducted by the Solar-Terrestrial Environment Laboratory, Nagoya University in cooperation with 27 organizations in Australia, Indonesia, Japan, Papua New Guinea, the Philippines, Russia, Taiwan, and the United States (Yumoto et al., 1992). In this paper, we review the initial results obtained from the 210° MM project; (1) a northern and southern hemisphere asymmetry for sudden commencements (sc) and sudden impulses (si), (2) low-latitude aurorae, (3) cavity-like and field line Pc 3-4 resonances stimulated by sc and si, (4) peculiarities of Pc 3 at low latitudes, and (5) the latitudinal profile of Pi 2.

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Measurements of F region vertical drift, V_z made at Kodaikanal (dip 4°N) on 133 days during March 1991-February 1992 under non-equatorial spread-F(ESF) conditions, are analysed for the characteristics of short-period (5-33 min) variations in V_z in the evening hours (1630-0130 IST). The spectral content of the fluctuations in V_z is found to depend on local time. The amplitude of the fluctuations, quantified in terms of the variance (σ²), increases during the period of postsunset enhancement of upward vertical drift and decreases thereafter reaching a minimum during 2200-0000 IST. In consonance with this, while functuations in V_z in the entire band 5-33 min manifest in the postsunset hours, the longer-period (13-33 min) components dominate thereafter (2200-0000 IST). The amplitude of the fluctuations and its day-to-day variability are higher in local summer than in local winter. On a day-to-day basis, the amplitude of V_z functuations increases with peak height in the interval 1756-2004 IST corresponding to the epoch of the evening enhancement in V_z. The results support the view that the short-period variations in F region vertical drift near the dip equator during the evening hours could be due to electric fields associated with the commonly occurring atmospheric gravity waves.

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Recent development of the technique of computerized tomography has provided a new tool to produce two dimensional (i.e., in a vertical slice) images of electron density structure in the ionosphere by utilizing the data of total electron content (TEC) obtained by trans-ionospheric satellite beacon measurements. In this paper, a preliminary result of our simulation study on the application of three kinds of reconstruction algorithm, (1) the multiplicative algebraic reconstruction technique (MART) as a typical iterative method, (2) a method on the principle of maximum likelihood estimation (MML), and (3) the spline function method (SFM), both as non-iterative method, is briefly described from the viewpoint of comparison with respect to characteristics, merits and disadvantages among the three. It should be noted that (1) MART will be a more reliable method if we can remove its shortcoming, i.e., lack of objectivity in the determination of the end of iteration, and (2) both MML and SFM will become useful, provided that we can solve, what is called, the problem of ill-conditioned matrix in the case of MML, and confirm the effectiveness of any information criterion that prescribes the optimum number of knots and the order of B-spline in the case of SFM.

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The results of an experiment on the MU radar to observe VHF radio wave scattering structures around the jet stream and frontal disturbances in the upper troposphere and tropopause region are reported. The experiment used spaced antenna techniques which can provide high resolution measurements of the wind vector and of the spatial scales and orientation of the structures which are generally associated with turbulence. The main spatial scale parameter examined here was the angular distribution or aspect sensitivity of the scatter. The orientation of the scattering was found in both the vertical and horizontal planes. Rapid variations of scattering orientation in the vertical plane were observed which can be expected to influence high time resolution velocity measurements, particularly vertical velocity. In the horizontal plane, the orientation of scattering structures showed some relationship to wind minima and shear features.

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Highly relativistic electron precipitation (HRE) events which occur in the mid-latitude and auroral regions last 2.5 days on the average, peaking in the magnetosphere daily near local noon. Furthermore, they can recur every 27 days for several synodic solar rotation periods, and become most intense and frequent during the minimum of the solar cycle. These events are described in terms of their spatial and temporal extent and their spectral characteristics. A detailed sounding rocket study of a relatively weak event in May, 1990 at Poker Flat, Alaska gave energy depositions from which modeling calculations have yielded O³ depletion estimates in excess of 25% near 75 km altitude. These depletions would hardly affect the UV flux reaching the stratosphere below, but could alter the thermal balance in the 60-75 km altitude region in the mesosphere. Further analysis for that HRE has shown the possibility of Joule heating effects near the polar cusp of up to 3°/day depending on the magnitude of the electric field. The mesospheric heating caused by more intense events studied with SAMPEX (Solar Anomalous Magnetospheric Particle Explorer) is compared with the earlier May 1990 event to demonstrate the global impact of HRE events on the chemical and thermal characteristics of the neutral atmosphere.

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Recent research suggests that variability in the troposphere and stratosphere on the scale of a decade is associated with the sunspot cycle. Our work demonstrates that a 10-12 year oscillation of the geopotential height in the lower stratosphere south of 45°N is well correlated with the sunspot cycle, and that it is associated with changes on the same time scale in the temperature of the middle and upper troposphere. Preliminary work links these temperature changes to changes in the vertical motions in the tropics and subtropics.

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