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Since 1980, we have detected impulsive noise bursts of seismogenic emissions at 82 kHz, 1525 and 36 Hz with a multipoint detection network around Tokyo region. This system has recorded EM signals prior to several earthquake events and two volcanic eruptions at Mt. Mihara, 1986 and at Mt. Unzen, 1991. By our statistical analysis of these emission characteristics using the last 29 events over the last decade, impulsive magnetic energy generated with rock crash at focus area is carried along the magnetic flux from focus to epicenter, and this magnetic intensity variation seems to be induced the electromagnetic waves at the ground surface. The results of our underground measurement in the tunnel support above explanation.

Simultaneous TV camera data were obtained at three nearly geomagnetic-conjugate stations: Husafell in Iceland, and Syowa and Asuka in Antarctica, on September 9-10 in 1991. Of the two southern stations, Syowa is more nearly conjugate to Husafell. With two stations in the Antarctica, the field of view in the southern conjugate area extends longitudinally to ∼ 1600 km at auroral heights, making it possible to investigate the spatial characteristics of auroral conjugacy. When the correlation of auroral shape and intensity between conjugate areas was examined, an interesting event was discovered in the geomagnetic recovery phase in the midnight sector. During this event, good correlation was maintained between Husafell and Asuka while no correlation existed between Husafell and Syowa, suggesting a large (500-800 km) longitudinal displacement of conjugate auroras. The cause of the longitudinal displacement is discussed.

A new-type source of power line harmonic radiation (PLHR) is described in this paper to point out its significance to the magnetospheric emissions. Characteristic electromagnetic fields were observed over the Kola Peninsula, northern Russia, during the flight of the balloon B15-2N in 1982. The source is characterized by (a) the fundamental frequency of 24.4 Hz, (b) the harmonic spectrum continuously extending up to VLF, and (c) the isolation from commercial power lines. These characteristics are different from the previously reported PLHR sources that could trigger the magnetospheric emissions. Based on the low impedance field and the amplitude variation along the balloon trajectory, the source can be modeled by a horizontal electric dipole or a horizontal magnetic dipole, and then the source distance is estimated within the induction area of a few hundred kilometers. The most probable source is an electric railroad or a single-phase power line, driven by an isolated power generator, and located on the Kola Peninsula. Estimating the radiation power through the ionosphere, it is shown that enough power to trigger magnetospheric emissions may be radiated into the magnetosphere from the source. Therefore, it is suggested that the source can be recognized as a new-type PLHR source possibly related to magnetospheric emissions.

Simultaneous TV data of auroras were obtained at 3 nearly geomagnetic conjugate stations: Husafell in Iceland, and Syowa and Asuka in Antarctica, on September 9-10 in 1991. Active, pulsating auroras were found between 22:54 and 22:57 UT in both hemispheres. Pulsating spatial pattern, intensity variation, period and periodicity of periodic type pulsating auroras were used to examine possible conjugacy in the observational areas. The results reveal a distinct lack of correlation between pulsating auroras in geomagnetically conjugate stations during the event in question.

The purpose of this paper is to examine the possible seismic influence on the propagation of magnetospheric whistlers at low latitudes on the basis of long-term data observed at Sugadaira (geomagnetic latitude 25°N) during 1970–1978 and at Sakushima (24°) during 1980–1982. It is found from statistical analysis of the Sugadaira data that anomalous whistlers whose dispersion value is greater than twice the typical value, exhibit a substantial increase in occurrence during seismic activity in the geographic longitude sector of 100°E–160°E, and this association becomes more enhanced when we take the occurrence of any whistlers (short, long and/or anomalous) during the summer time (June–August). Finally, with increasing anomaly (that is, anomalous dispersions and summertime), we have found an exceedingly high statistical correlation between the summertime anomalous whistlers at Sakushima and the seismic activity satisfying the above condition. We have studied whistler characteristics for all earthquakes. These studies have indicated that a considerable number of cases of earthquakes are of a type such that several earthquakes occur successively; and, correspondingly, we observed an enhanced occurrence of anomalous whistlers during such prolonged seismic activities. Several isolated and intense earthquakes are characterized by the appearance of anomalous whistlers prior to and after the earthquake. In conclusion, we claim that whistlers with anomalous dispersions are likely to be closely correlated with earthquakes occurring in the relevant longitude range, but we cannot make any definite statement on the use of low-latitude whistlers as precursors of earthquakes and further detailed studies are obviously required on this subject. Some possible mechanisms of the earthquake-associated effect causing whistler propagation are discussed.

Since 1980, we have detected impulsive noise bursts of seismogenic emissions at 82 kHz, 1525 Hz and 36 Hz with a multipoint detection network around the Tokyo region and the Izu peninsula. In earlier times, this system has recorded EM signals prior to several earthquake events. And it has also recorded volcanic eruptions on 15 and 21 November 1986 at Mt. Mihara on Ohshima Island, on 12 July 1989 in Itoh Bay in the Izu peninsula region, and since June 1991 at Mt. Unzen on the Shimabara peninsula. To obtain a clear explanation of the source mechanism of these emissions, we are progressing with statistical analyses of these emission characteristics using the data of 29 events over the last 5 years.

Statistically improved results of power line radiation (PLR) over Eastern Asia observed at 50 and 60 Hz are described in this paper. A total number of 150 orbits, which had been observed from June 1984 to January 1986, by the Japanese scientific satellite OHZORA, are used to detect PLR over Eastern Asia around the Japanese Islands. Depending on the increase in the number of data points, the statistical characteristics of the background noise can be precisely determined by using the improved technique compared with the initial analysis. Statistically reasonable data points are detected as PLR based on the +3σ criterion, where σ is the standard deviation of the background noise. Therefore, the statistical reliability for rejecting the background noise is 99.85%. Then, these detected data are applied to the cause-and-effect test. When the statistically detected data points are placed on the map of Eastern Asia, the points cover Eastern Japan and the east coast of China for 50 Hz, and they cover Western Japan for 60 Hz. The maps of the detection ratios and those of the average field strengths indicate the positive correlation with the ground maps of the electric power generation at 50 and 60 Hz. The positive correlation is more clearly seen at 50 Hz since the background noise is somewhat weaker than that at 60 Hz. This close relationship between the satellite observation and the electric power generation suggests that the detection of PLR is not caused by chance, and that PLR penetrates into the ionosphere and propagates approximately just upward. The decrease of field strength with altitude can be interpreted as the gradual decrease of the refractive index from to 700 km. Therefore, the detection ratio and the average field strength with respect to the satellite altitude suggest PLR propagating from the bottom of the ionosphere. According to these observational results, it is concluded that PLR in Eastern Asia is high above the high electric power generating regions over Japan and China, and that the satellite observation is capable of estimating PLR field below the ionosphere. These results are the first direct indication that the PLR field is enhanced over the high electric power generation region, and is penetrating into the ionosphere.

The direction finding of precursory radio emissions associated with earthquakes is proposed, based on the simultaneous measurement of the waveforms of multiple electric and magnetic field components at ELF (1.525 kHz ± 5 Hz) and ULF (0–10 Hz) at a few stations. This measurement enables us to determine the wave mode of the observed signal (for example, its direction of arrival) by measuring such parameters as the wave impedance, wave polarization and wave coherence. From these observations we hope to be able to obtain the first convincing evidence on the precursory emissions of earthquakes.

Since 1976 a total of 3500 orbits of data from the Isis-1 and 2, Kyokko and Akebono satellites have been analysed to produce some new observational results about polar VLF and ELF emissions at Arctica and Antarctica. By mapping the distribution of the occurrence of the emissions in the polar regions the source of Electrostatic Ion Cyclotron (EIC) emissions has been located. 1. (1)The EIC emissions with clear harmonic structure at the local ion cyclotron frequency of wide V-shaped auroral hiss emissions were always located at altitudes about 3000 km above an auroral arc. 2. (2)Over 85% of EIC emissions were observed at the active auroral area of the night-side. 3. (3)Direction finding observations using the Akebono satellite showed that all sources of VLF saucers were located below the altitude of the satellite orbit.

A multipoint network was constructed in the Tokyo area for earthquake prediction using seismogenic electromagnetic emissions. The network consists of eight observation points within 50 km of each other.Each point has a digital direction-finding detector with two loop sensors tuned to 82 kHz. The output signals of the receivers are added into a digital vector composition circuit to obtain the direction angle of the source point,and this signal is telemetered to the central computer.To protect from false alarms caused by local man-made noise interference,the warning is announced only when there is a high cross-correlation between almost all detectors pointing to one small area. The mechanism of these earthquake precursors can be explained as electromagnetic emissions from the rocks around the focus when they are crushed completely by the distortion pressure. These emissions propagate along the fault plane as an EM surface wave mode and radiate from the slit antenna formed by the intersection of the fault plane and ground surface.In the last five years, we have detected impulsive noise bursts of seismogenic emissions at 82 kHz, 1.525 kHz, and 36 Hz using our multipoint detection network around the Tokyo region and Izu peninsula. This system has recorded EM signals prior to the following events: volcanic eruptions on November 15 and 2 1, 1986 at Mt. Mihara on Ohshima Island, and on July 12, 1989 in Itoh Bay in the Izu peninsula region, and also a minor earthquake on October 14, 1989 at Ohshima Island.

The VLF wave instruments on board Akebono (EXOS-D) involve a wide band analyzer (WBA), multi-channel analyzers (MCA), Poynting flux analyzers (PFX), ELF frequency analyzers and a vector impedance probe (VIP) and cover a frequency range from a few Hz to 17.8kHz for electric and magnetic field components. The main objectives of the wave observations are to investigate the wave phenomena closely associated with energetic particle precipitation in the auroral zone and the physics of wave-wave and wave-particle interaction phenomena. In order to clarify these wave characteristics, the determination of the wave normal direction and the direction of the Poynting vectors are essential. Our VLF instruments, especially PFX and ELF, are designed to satisfy such requirements. The present paper introduces all the subsystems of the VLF instruments and some preliminary results of observations to show the characteristic features of each subsystem.

At the time of the major volcanic eruptions on November 15 and 21, 1986 at Mt. Mihara, Izu-Ohshima Island, Tokyo territory, Japan, a detector from a multipoint direction-finding network to detect electromagnetic emissions was operating. Since October 20, 1986 impulsive noises at 82kHz were recorded, and these anomalous burst-like noise observations increased after November 3. At 10-16 JST (Japanese Standard Time, UT+9 hours) on November 14, several strong noise bursts were observed, and the first major eruption occurred at the main summit crater of this volcano at 16 JST on November 15. At 10-12 JST on November 21, noise bursts were observed and four hours later, 19 new craters erupted suddenly on the side slope of the mountain, both in and outside the caldera, simultaneously with the intrusion of dykes in the mountain body. These records are the first observations of electromagnetic emissions as precursors to volcanic eruptions ever recorded. The authors present this paper in the form of a short note for data presentation, because analysis of these data and comparison with other observations is still continuing.

Narrow-banded ELF emissions in the frequency band of 100–500 Hz have often been observed in the VLF data received at Syowa Station ( L = 6.1) in Antarctica from ISIS 1 and 2. The occurrence distributions of narrow-banded ELF emissions over the southern polar region have been studied statistically. It is found that emissions mostly occurred in the evening 17–24 M.L.T. sector and in the region of 65°–75° invariant latitude associated with V-shaped VLF hiss emissions. The emissions are correlated with disturbed geomagnetic activity and the occurrence region shifts to lower latitude in association with increased geomagnetic activity. It is also found that emissions maximize during austral winter season, from April to July. The emission frequencies are strongly dependent on the satellite's altitude. These results suggest that narrow-banded ELF emissions are excited in the topside ionosphere by upflowing ion or downflowing electron fluxes and that the growth rate strongly depends on the ambient electron density. We also discuss the relation between the emissions observed by the satellite and on the ground.

Seasonal and diurnal variations of Pc 3-5 magnetic pulsation powers have been examined using 2 years of magnetic data from geomagnetically conjugate stations, Syowa in Antarctica and Husafell and Tjoernes in Iceland. The magnetic pulsation powers are found to be relatively higher at the winter hemisphere station than at the summer station. The pulsations observed during equinox show a diurnal dependence, i.e., that the power density is higher in the geomagnetic morning at the stations in Iceland than at Syowa, and this relationship is reversed in the afternoon. The power density ratio of Pc 3 pulsations between the conjugate stations, which is associated with the seasons and with local time, is higher than that of Pc 5. These characteristics can be attributed to the effects of sunlight in the ionosphere, i.e., Pc 3-5 pulsations are shielded when the waves propagate from the magnetosphere to the ground through the sunlit ionosphere.

1976年南極昭和基地において,ISIS1,2人工衛星からのVLF観測テータの受信が行われた.これらのVLFエミッションのテータと地上で同時刻に観測されたVLFエミッションおよひオーロラの観測テータとの比較を行った.一般に,ISIS 2が高緯度領域から低緯度領域に移動していくにつれ,ヒスエミッションとソーサーエミッションが順々に観測される.解析結果によると,ヒスエミッション領域からソーサーエミッション領域に移る境界付近か,地上て見られるもっとも低緯度側のオーロラ・アークを通る磁力線の位置に対応していることが明らかになった.地上て観測されたヒスエミッションのスペクトラムと人工衛星て受信されたヒスエミッションのスペクトラムを比較した結果,地上と人工衛星とを磁力線て結んた領域て観測されるヒススペクトラムは似ておらす,むしろ,人工衛星のサフサテライトポイントが,昭和基地と同じ地磁気緯度付近にある時に観測されるヒススペクトラムが互に類似していることがわかった.このことはヒスエミッションが,人工衛星の高度(h=1400 km)から地上まで磁力線に沿って伝搬していないことを示している.Ray pathの計算を行った結果,地上て受信されるヒスエミッションは,人工衛星の高度からノンダクトな伝搬路をとることが推定された., ISIS VLF data were received at Syowa Station, Antarctica in 1976. These data were compared with VLF and auroral data simultaneously observed on the around. In general, hiss and saucer emissions were succesively observed on ISIS 2, when ISIS 2 moved from the polar cap towards the low latitude. It is found that the geomagnetic field lines through a northernmost auroral arc are located between the occurrence regions of hiss and saucer emissions. It is also found that spectra of hiss emissions observed on the ground (Syowa) are not similar to those of VLF emissions observed in the region connected with field line at the satel-lite altitude, but are similar to those of VLF emissions observed near the same geomagnetlc latitude as that of Syowa Station. The result suggests that auroral hiss emissions do not propagate along the geomagnetic field lines from the statellite height (～1400 km) to the ground. The calculation by means of the ray theory suggests that hiss emissions propagate along a non-ducted path from the satellite height to the ground

Conjugate observation of VLF emission was carried out at Kitdalen (69.1°N, 20.3°E geographic, 65.5°N, 105.3°E geomagnetic, L=6.0) in Norway and at Syowa Station (69.0°S, 39.6°E geographic, 66.2°S, 70.5°E geomagnetic, L=6.1) in Antarctica in February 1980,and also at Andφya (69.2°N, 16.0°E geographic, 66.0°N, 102.2°E geomagnetic, L=6.1) in Norway and at Syowa in March 1982. During these campaign periods, periodic VLF emissions were often observed at both stations in opposite hemispheres. A typical periodic emission event observed at both stations was chosen for cross spectral analysis of the emission period. The results show the characteristics of "symmetrical three-phase emission" reported by BRICE (Radio Sci., 69D, 257,1965) as three wave packets, which were symmetrically spaced along the line of force, were echoing in the magnetosphere. Though the geomagnetically conjugate point of Syowa is located about 1800km far from Kitdalen or Andφya, the common nature of the emissions observed at both stations suggests that the periodic emission which originates from the common source in the magnetosphere can spread more than 1800km at the ionospheric level. This observational result is compared with the ray tracing calculation. It is concluded that if the periodic emissions are guided by a field-aligned duct and the duct is terminated at an altitude of 6000km, the periodic emissions can spread as far as the observed distance.

Occurrence distributions of narrow-banded ELF emissions over the southern polar region have been studied statistically from ISIS-1 and -2 VLF data which were received at Syowa Station (L=6.1) in Antarctica. It is found that emissions occurred mostly during the evening to the pre-midnight of 17-24 MLT and in the region of 65°-75° invariant latitude associated with V-shaped VLF hiss emissions. The emissions occurred during disturbed geomagnetic activities and the occurrence region shifted to lower latitude in association with geomagnetic activities. It is also found that the emissions have their occurrence maximum during the austral winter season from April to July. The emission frequencies are strongly depending on the height of the satellite position.

Global distributions of auroral hiss and VLF saucer emissions have been examined by using VLF data obtained from the three satellites, EXOS-A, ISIS-1 and -2. These VLF data were received at Syowa Station in Antarctica. From the observations of hiss and saucer emissions on five pairs of satellite paths in which the two satellites traversed the auroral zone with a time difference within one hour, it is seen that the location of the hiss and saucer emission regions do not change too much during that time. Furthermore, it is seen that the equatorward boundary of the hiss emission region is located near the position of the auroral oval statistically given by THOMAS and BOND (Planet. Space Sci., 26,691,1978) for each value of Kp index. These results suggest that the hiss and saucer emission regions exist not only statistically but also they are maintained over the time scale of one hour.

A comparison of total ozone amounts and lower stratospheric temperature during the 1982 stratospheric sudden warming in the Antarctic is made by the TIROS Operational Vertical Sounder (TOVS) data of NOAA-7 received at Syowa Station. A method assuming a vertical ozone profile is applied to obtain total ozone amounts. The total ozone can be determined independently of the surface measurements. A good agreement between the total ozone amounts derived from satellite data and those of Dobson measurements is seen at Syowa Station. RMS error is 12 DU ((10)^・atm・cm). A good correlation between the total ozone and the lower stratospheric temperature is observed in the Antarctic. Patterns similar to the wave number 5 structure of the total ozone during the Southern Hemisphere summer are seen during the 1982 sudden warming.

Observations of the electromagnetic field strength of power line radiation over northern Europe were conducted under the geomagnetically active conditions using the balloons B_-1N on March 20,1982 and B_-2N on November 23 and 24,1982. Substorms occurred during the both flights. A substorm effect on the strength of the electromagnetic field of the power line radiation was investigated at the harmonic frequencies of commercial power line frequency, 50Hz in the frequency range from 40Hz to 1kHz. The strength of the power line radiation at the harmonics of 50Hz in the frequency range from 200 to 900 Hz enhanced during the substorms. A great increase of strength was observed at 300,450 and 600Hz on the balloon B_-1N, and at 300,450Hz on B_-2N. However, the strength at 50,100,and 150 Hz did not enhance more than 3dB during the substorms. It is concluded that the strength of the power line radiation enhanced at higher harmonics of 50Hz during a geomagnetic substorm.

A receiving system for High Resolution Picture Transmission (HRPT) data of the TIROS-N/NOAA series meteorological satellites has been installed at Syowa Station, Antarctica. One of the TIROS Operational Vertical Sounder (TOVS)-HIRS/2-data were analyzed and the vertical temperature profiles were derived. The statistical method and the minimum information method were used to retrieve the temperature, and the average errors were estimated as 3℃ and 6℃ respectively compared to the radiosonde observations made at Syowa Station.