A new Hα solar telescope for the forecast of solar activity and the research on energetic phenomena of the sun has been constructed at Hiraiso Solar Terrestrial Research Center in Japan (Regional Warning Center of IUWDS). Its main features are (1) high resolution digital full-disk Hα images with a 2 K by 2 K CCD, (2) real-time data processing with an automatic frame-selection technique, (3) spectroscopic observation with an automatic wavelength shift of Hα Lyot filter. Because of these advanced features, continuous observations of the sun with this system will provide more reliable data for the forecast of solar activity and its influence on the space environment.

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The global magnetic field of the Sun is regarded as consisting of 4 main field systems: 1) the axial dipole field, which is most pronounced at polar latitudes (ψ 6gt; ∼50°); 2) the inclined dipole field in the equatorial region (ψ < ∼50°); 3) the quadrupole component (a system of super giant cells with a size of ∼80°-110°) that manifest itself in the form of a 4-sector field structure; and 4) the multipole component of orders higher than quadrupole. The global field and each of its components are quantitatively characterized by the total and partial magnetic field indices. The absolute and relative contribution of each field component in different phases of the solar cycle are displayed for solar cycles 20, 21 and 22. The physical meaning of solar cycle reference points is discussed.

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The soft X-ray telescope (SXT) aboard the Yohkoh spacecraft has revealed coronal X-ray jetsassociated with small flares in X-ray bright points (XBPs), emerging flux regions (EFRs), and active regions (ARs). These observations of X-ray jets are reviewed mainly from a morphological perspective. In particular, various observational evidence of magnetic reconnection in X-ray jets is discussed. It is suggested that magnetic reconnection between emerging magnetic flux and the coronal magnetic field is a key physical process for producing these jets.

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The possible contributions of the SOHO to the Solar Terrestrial Energy Program are discussed. Several SOHO measurements and observations will be of interest for the study of the energy flow in the solar terrestrial system: - the total solar irradiance or solar constant will be monitored with an accuracy of about 0.15% by solar radiometers in one of the helioseismology instruments, - the solar EUV irradiance will be measured directly by an EUV monitor (at 305 Å) and obtained at several wavelength bands between 150 and 1600 A by integration of spectroscopic images, - synoptic maps of the sun at different levels of the chromosphere, transition region and lower corona obtained in extreme ultra-violet (EUV) will be produced by the SOHO telescopes and spectrometers, - solar magnetograms with about 4 arc second resolution (2'' pixels) will be produced several times per day, - the evolution of the large coronal structures that shape the solar wind, as well as the coronal mass ejections will be followed by two coronagraphs and by a solar wind anisotropy measuring instrument; the latter generate the solar wind disturbances that are cause of the most energetic magnetic events in the geosphere, - the elemental, isotopic and charge state composition and energy distribution of the ions that form the solar wind, as well as of the energetic particles that will reach the earth magnetosphere, are determined in SOHO by a set of time-of-flight and solid state detectors.

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A significant fraction of the energies emitted by the sun is conveyed by coronal mass ejections, which are very likely to appear as interplanetary magnetic clouds in the heliosphere. The helical field lines in a magnetic cloud are kept untangled to the surrounding spiral field lines, which permeate the solar wind in the heliosphere, by a polarization current induced on the magnetic cloud's periphery. The induced current and the current carried by a passing magnetic cloud may exert large forces on the currents of heliospheric current sheet, which interfaces oppositely directed spiral field lines. Severe deformation of the heliospheric current sheet, which depends also on the latter's configuration, may change significantly the orientation of the interplanetary magnetic field in the vicinity of the passing magnetic cloud. The transitory deformation of the heliospheric current sheet may incur a large southward component in the interplanetary magnetic field. Such a southward component, when incident on the earth's magnetosphere, may trigger efficient transfer of energies from the solar wind to the magnetosphere.

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We present an overview of direct ion and electron observations of the polar wind and suprathermal auroral ions from the plasma instruments on Akebono. In the polar wind, the observed H⁺ ion reaches a velocity of 1 km/s at 2000 km altitude, as does He⁺ ion near 3000 km and O⁺ ion near 6000 km. At high altitudes, the O⁺ ion constitutes a significant component of the polar wind flow contrary to most polar wind model predictions. At 2000-4000 km, the H⁺ ion velocity in the polar wind is strongly correlated with the ambient electron temperature. The electron temperature (averaged thermal energy) in the upward magnetic field direction is a factor of 1.5-2 higher than that in the downward and field-perpendicular directions. This results in an upward heat flux which is comparable in magnitude to the heat flux carried by energetic (>10-eV) photoelectrons. The observed electron temperature anisotropy and correlation with ion velocity are consistent with the polar wind being driven by a large ambipolar electric field resulting from the presence of escaping atmospheric photoelectrons (required to maintain quasi-neutrality along the field line). At auroral latitudes, significant fluxes of “minor ions” are frequently observed, particularly atomic N⁺ and O⁺⁺ ions and molecular NO⁺, N₂⁺, and O₂⁺ ions. The occurrence of molecular ions at high altitude (>3000 km) during extended periods of auroral activity points to their fast energization at the F-region and topside ionosphere. In the 3000-6000 km altitude region, transverse ion energization occurs frequently both on the dayside and the nightside. Different ion species are energized in the perpendicular direction to tens and at times hundreds of eV over a narrow spatial extent, and appear as “ion conics” at higher altitudes as they spiral up the field lines. In the 3000-9000 km altitude region, the average energy of the observed ion conics in the dayside auroral zone increases with altitude.

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The Active Plasma Experiment (APEX) uses intensive electron beam emission for the study of dynamic processes in the magnetosphere and upper ionosphere. The beam energy and current is as high as 8 keV and 100 mA and the pitch angle of the emission varies in the range from 50° to 80°. The basic cycle of electron injection is formed by current pulses of different duration, intensity and frequency. The spacecraft potential is balanced by a low energy xenon plasma generator during the electron beam injection. The response of the environment is studied by the PEAS charged particle spectrometer working in the energy range 0.1-25 keV. The common response to the beam emission is the increase of the intensity of the registered electrons with energy less than 2 keV. Under some circumstances (the satellite position, the injector regime, the beam direction with respect to the magnetic field etc.), strong electron fluxes of the order of 10⁷ cm^-2sec^-1keV^-1 have been observed. The energy of these fluxes is in general a rising function of the mean current of the emitted beam but never exceeds the beam energy. The energy-angular distribution exhibits a complicated structure with the maximum energy located at the pitch angle which corresponds to that of the emitted electron beam.

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This letter reports on leakage ions from the low latitude boundary layer (LLBL) to the magnetosheath boundary layer (MSBL) as observed by Geotail at the dayside magnetopause. A reconnection of the interplanetary magnetic field (IMF) with magnetospheric field lines is shown to be responsible for the leakage. Based on analysis of a variation in lower cut-off levels occurring in the velocity distribution function of the leakage ions, we propose a “velocity filter effect” model with a finite source region to explain this variation. The location of the reconnection region is subsequently calculated to be 2.2R_E north of the geomagnetic equatorial plane under the proposed velocity filter effect model.

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The D_st and SD variations of ionospheric total electron content (TEC) around equatorial anomaly crest region during SC geomagnetic storms have been statistically analyzed by using the continuous measurements of total electron content at Limping Observatory (25.00°N, 121.17°E geographic, 14.3°N, 191.3°E geomagnetic) from March 1977 to December 1993. The characteristic variations of D_st and SD of TEC are described and compared with the D_st and SD variations obtained from geomagnetic horizontal component recorded at Lumping Observatory. Some qualitative explanations are also attempted.

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A new experimental method is suggested to recognize a type of the incident magnetospheric wave following by the time and frequency dependency of the azimuth angle of geomagnetic pulsations close to the terminator. The main idea is based on the fundamental differences between the ionospheric transformation of the Alfvén and magnetosonic waves. The Alfvén waves are associated with some kind of field aligned currents which cannot penetrate into the atmosphere and spread over the high conductive ionosphere. Magnetic effect on the ground is defined mainly by the ionospheric currents caused by the Alfvén wave. In contrast, in the case of magnetosonic wave, the ground current system provides the main contribution to the total current and going from the daylight ionosphere to the night one does not markedly affects on the total current. Equatorial observations revealed the horizontal orientation angle in different frequency ranges. This is inclined to think that in the cases have been under the consideration the oscillations within the range 50∼500 s are generated by the Alfvén waves.

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Ionograms and magnetograms at Great Wall (62°13'S, 58°58'W), Antarctica, were used to study the ionospheric effects of the March 13, 1989 magnetic storm in sub-auroral locations. The virtual height of the F region (h'F) increased and the critical frequency (f_oF₂) decreased rapidly just after the storm sudden commencement (SSC). Then the spread F appeared and lasted about five hours. During the main phase of the magnetic storm the ionosphere encountered severe absorptions, but large enhancements in h'F and associated depressions in f_oF₂ sometimes were still observed. On the second and third nights after the SSC auroral type sporadic E and night E layers were observed, showing peak electron densities as high as 7.5 × 10⁵ el cm^-3. The causes of these phenomena are discussed. Behaviours of h'F and f_oF₂ from four ionosonde stations in the same longitude sector (Great Wall, Port Stanley, Cachoeira Paulista and Fortaleza) show that the higher the station's latitude is, the more severe absorptions occur, and the longer the depressions of f_oF₂ last.

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In the limit of an isothermal atmosphere without dissipation, the equations governing atmospheric motions admit solutions corresponding to “free” (unforced) oscillations for discrete zonal wavenumbers and periods. Global oscillations belonging to the rotational subclass are referred to as free Rossby waves or Rossby normal modes. Despite the existence of mean winds, nonisothermality, and dissipation, atmospheric manifestations of these waves apparently exist. To date the study of such oscillations has been confined mainly to the troposphere and stratosphere (0-50 km), which includes the source region for the disturbances. However, there is increasing evidence that the effects of free Rossby waves extend into the mesosphere/lower thermosphere (ca. 80-150 km) and ionosphere (ca. 90-400 km). The present work draws upon recent numerical modeling results and data analyses as a framework for discussing the penetration of planetary wave effects into the upper regions of the atmosphere, especially the ionospheric dynamo region (ca. 100-170 km) and the electrodynamic interactions which ensue there. Attention is primarily focused on the westward propagating normal modes of wavenumber s = 1 (periods of 5, 10 and 16 days), and the so-called “2-day wave” which is normally associated with the mixed Rossby-gravity mode with s = 3.

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Numerical simulations have been performed to investigate global changes of the neutral gas dynamics and composition in response to high-latitude energy input. Four simulations have been performed, at equinox, using a two-dimensional, time-dependent model of coupled dynamics and composition for modeled storms with various durations ranging from 3 hours to 24 hours. In order to study the dominant mechanisms responsible for the composition changes, a term analysis of the neutral composition equations has been performed. The major results are as follows; (1) the boundary between the regions of upwelling and of downwelling lies at 54° latitude for the storm heating longer than 9 hours, and 49° latitude for the 3 hours heating; (2) the boundary between the regions of positive change in mean molecular mass (m₀) and negative one lies at49° latitude for the 3 hours heating, but it reaches 38° latitude for the 24 hours heating; (3) the boundary in Amo is located equatorward of the corresponding boundary between upwelling and downwelling, which means the penetration of the region of positive Δm₀ into the region of the downwelling; (4) the degree of penetration largely depends on the duration of storm heating; (5) the primary cause of the composition changes for the storm heating longer than 9 hours is by horizontal and vertical advection associated with a storm circulation; for the 3 hour storm vertical advection from atmospheric gravity waves is the primary cause of the composition changes.

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The present paper reviews dynamical features of the mid-latitude ionosphere and thermosphere in the Asian sector as quantified by the MU radar at Shigaraki, Japan (35°N, 136°E) and compares these with dynamics reported for other locations. The thermospheric wind and temperature in the Asian sector differ from the wind and temperature measured at other mid-latitude locations. Furthermore, the perpendicular plasma drifts have strong resemblances to those predicted by current models, but their seasonal trends suggest a strong conjugate effect that has not been fully incorporated into our expectations of local behavior. These results provide additional evidence that global features cannot be described by a simple zonal mean. Finally, two features related to gravity waves are discussed. Gravity waves seem to be ubiquitous in the thermosphere and play an important role in creating a variety of electron density fluctuations and irregularities in the mid-latitude ionosphere. Tracking the progression of ionospheric gravity-wave effects between MU radar beams has allowed gravity wave packets to be identified and their dispersion relation to be determined. The character of ionospheric irregularities observed are consistent with their seeding by the Perkins mechanism.

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WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite (UARS), has been in orbit since September, 1991 and by 1995 had accumulated more than 14 million images of the upper atmosphere. It employs Doppler imaging using a Michelson interferometer and CCD camera to obtain winds, temperatures and volume emission rates of selected airglow emissions in the visible and near-IR covering the altitude range 80 to 300 km. In this paper we first present wind and emission rate measurements from the O(¹S) 557.7 nm night airglow emission resulting from the recombination of atomic oxygen. From these data atmospheric tides have been found to have a profound influence on the distribution of atomic oxygen. A strong longitudinal modulation in winds and emission rate has been found as well, indicating large scale planetary disturbances in atomic oxygen. Observations of daytime 557.7 nm green line emission are then presented, which arise mainly from solar EUV excitation. From these data one can see the response of the green line emission to the solar flux, as well as planetary scale disturbances. During the daytime, scattering from polar mesospheric clouds provides further evidence for the strong dynamics of this region of the atmosphere.

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Cross tropopause air mass flux plays an important role for the exchange of minor constituents between the troposphere and stratosphere. In general, one can assume net upward air mass fluxes in the tropics and net downward flow in the extratropics. Yet the detailed picture exhibits coexisting up- and downgoing meso-scale flows in the tropopause region probably occurring at all latitudes. This feature of stratosphere-troposphere exchange is particularly addressed in the paper with emphasis on the extratropics. Tropopause depressions like folds and cut-off lows are meso-scale features heavily contributing to downward transport at middle and high latitudes. Statistics derived from global analyses for the period 12/1983 to 11/1991 reveal that folding and cut-off low activity is about twice as strong in the northern hemisphere than in the southern one. A case study of a folding event overthe North Atlantic using a mesoscale meteorological model shows that downward cross-tropopause fluxes are partly compensated by upward fluxes. The ratio of up- and downgoing air mass is about 2:3 during the simulated episode. Note that the upward flux is not a mere return flow. It is expected that this air mass exchange leads to structural and chemical modifications of the lowest stratosphere.

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Department of Physics and Astrophysics of the Nagoya University, Fujitsu Laboratories Ltd. and Fujitsu VLSI Ltd. are developing millimeterwave superconductive receivers. In 85-115 GHz band, these laboratories have constructed an ozone sensor for monitoring strato-mesospheric ozone employing a superconductive receiver with a receiver noise of 34 K (SSB). The spectrometer is an acousto-optical type and covers a frequency range of 70 MHz with a frequency resolution of 35 kHz. Using the load switching technique, observations are carried out and vertical profiles of ozone concentrations are retrieved in the altitude range between 30 and 80 km.

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We have carried out tropospheric observations by the MU radar (VHF-band) and meteorological radars (C-, Ku- and X-bands) for three weeks during the Bain (early summer rain) season in 1991 (17 June -8 July). We produced a complete data set of three-dimensional wind velocity, turbulence parameters, cloud and precipitation with high reliability and resolution. Results of the data analysis show that a meso-α-scale cyclone on the Baiu front has an asymmetric hierarchical structure of vertical velocity fluctuation distributions, which consists of meso-β-scale cloud clusters (with strong upward velocities and rainfalls) and meso-γ-scale developing clouds (with remarkably strong events). Further, they are restricted by the lowest level of the stratiform turbulence near the tropopause and the frontal surface and are especially activated near the warm and cold fronts on the ground in the cyclone center.

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The Quasi-Biennial Oscillation (QBO) in the equatorial stratosphere affects the extratropical cyclonic vortex in the stratosphere by disposing it to act in either of two regimes: weak and warm in the east years of the QBO versus cold and intense in the west years. This influence of the QBO is, however, thwarted at the peaks of the 11-year sunspot cycle: at low solar activity the extratropical vortex reacts as expected, but at high solar activity the QBO signal is reversed. The high interannual variability in the arctic stratosphere is responsible for the lack of ozone depletion on the large scale observed in Antarctica.

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The solar wind modulation of the energy distribution and flux of galactic cosmic rays causes 11 year cycles in the latitude distribution of air-earth current density in the global electric circuit. Similar changes occur with solar activity on the day to day time scale. At least 3 independent data sets correlate changes in tropospheric winds and vorticity with measured and modelled changes in air-earth current density in the troposphere. These are (1) the decadal oscillations in winter in the North Atlantic region, with period averaging 11 ± 2 years over the last 120 years, and which appear to have been phase locked to the solar cycle except for a period of generally low solar activity prior to 1925; (2) the decrease in 500 mbar Vorticity Area Index (VAI) in winter at times of Forbush decreases of cosmic ray flux; and (3) decreases of 500 mbar VAI in winter at times of solar wind magnetic sector boundary passages, when volcanic aerosols from Agung and El Chicon were in the global stratosphere, together with solar wind sector modulated relativistic electron precipitation. One possible physical mechanism connecting changes in air-earth current density with changes in tropospheric dynamics is via the accumulation of electrostatic charge at cloud tops affecting the microphysics of ice nucleation and precipitation, with consequences for latent heat release and the intensification of winter cyclones.

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