A formal performance test of the hypothesis that swarms are long-term precursors to major shallow earthquakes is in progress in the region of Pacific-plate subduction in Japan. The likelihood of the major earthquakes (JMA magnitude ≥ 6.8) that occurred in the region during the test period (1983-1998) was 5.04 times higher under the swarm hypothesis than under the stationary Poisson model; this result is inconclusive in terms of the proposed acceptance level of 20. The earthquakes were the Hokkaido-Toho-Oki earthquake (M8.1) of 4 October 1994, and the Sanriku-Haruka-Oki earthquake (M7.5) of 28 December 1994. The significance of the performance has been evaluated by a Monte Carlo study of the results since mid-1991. This shows that the Poisson model can be rejected at the 1% level, and that the results are consistent with the swarm hypothesis. The test is continuing.

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The shape of the distribution in field directions and VGP positions was studied by Bingham statistics applied to a paleomagnetic dataset from lavas for the last 5 my by McElhinny and McFadden (1997), which includes those with VGP latitude higher than 45°. Data from Hawaii clearly show an oval shaped distribution of field directions, elongated along the meridian plane, while distribution of VGP is almost circular. Analysis on the global data divided by latitudinal bands also indicate more elongation in field directions for low latitude bands. This feature was interpreted as a general indication of dipole nature of the paleomagnetic field. For Hawaii data, however, possibility of the Pacific Nondipole Low is also suggested due to the large elongation parameter and very high significance of Fisher distribution to describe the VGP positions together with the small ASD. Although this elongated shape in the distribution of field directions is not clear for most of the individual site, the directions of the principal axes are sensitive enough to depict this feature at almost all sites.

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We present ground-based millimeter-wave observations of the upper stratospheric and mesospheric ozone, conducted at the National Institute for Environmental Studies (NIES) in Tsukuba, Japan (36°N, 140°E). The measurements were started in October 1995. The millimeter-wave radiometer used for the present study is equipped with the superconductor-insulator-superconductor (SIS) mixer receiver and the acousto-optical spectrometer (AOS). Vertical profiles of ozone mixing ratio from 20 to 80 km were retrieved from the observed ozone spectra for 23 months from October 1996 to August 1998 by using the weighted-damped least squares algorithm adopted for differential emission. Vertical resolution is estimated to be 14 km from the averaging kernels. The total random error on the retrieval is estimated to range from 3 to 13% in summer, and from 2 to 9% in winter, respectively, between 38 and 76 km in altitude. The ozone number density at 38 km with the radiometer which was convolved with the vertical resolution of the lidar agrees well with that of the lidar within a systematic difference of 1%, indicating that the millimeter-wave data at 38 km are validated by the lidar measurements. Annual and semi-annual variations are clearly seen at 50 and 76 km, respectively, in the time series of the ozone mixing ratio observed during 23 months. The annual variation at 50 km is consistent with that in the climatological models. The semi-annual variation at 76 km observed in this work is similar to that of the Solar Mesospheric Explorer (SME) data, except that the ozone mixing ratio in spring measured with SME is about 1.7 times larger than that in autumn while those with the radiometer are almost same.

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The ponderomotive influence of ion cyclotron waves on the field-aligned distribution and motion of ions in the equatorial zone of the magnetosphere is examined. The hydrodynamic, quasi-hydrodynamic and “test-particle” approaches are used for the study of ponderomotive wave-particle interaction. Particular attention has been given to the challenging questions encountered in applying the general theory to the magnetospheric physics. The closed system of quasi-linear equations describing the ponderomotive effects is derived. Analytical investigation of the basic equations has demonstrated the diverse manifestations of the ponderomotive impact of ion cyclotron waves on the ion population in the magnetosphere. It is found that the redistribution of ion density under the action of ponderomotive force with increase in the wave amplitude follows the pattern of phase transition of the second kind. The density distribution changes qualitatively as the point in plane of the governing parameters of system crosses a demarcation line. It has been found that the magnetic equator is an attractor for heavy ion. The period of the finite (oscillatory) motion of a heavy ion, which is trapped in the potential trough in the vicinity of magnetic equator, depends on the wave frequency, wave amplitude, together with the energy of motion. In addition, the diffusion equilibrium of ions in a multicomponent plasma is considered, and the ponderomotive separation of ions in a binary mixture is demonstrated. It is shown that the heavy ions collect near the magnetic equator provided the waves are comparatively strong. It suggests that the ponderomotive effects play a part in formation of structure and dynamics of the magnetosphere.

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Japan's first Mars spacecraft PLANET-B was successfully launched on 4th of July, 1998 and was named “NOZOMI” after the launch. One of the scientific instruments is a unique electron temperature probe which was developed in Japan and has been used for more than 20 years on sounding rockets as well as on scientific satellites (Oyama, 1991). The electron temperature probe dubbed PET (Probe for Electron Temperature measurements) consists of two planar electrodes, 150 mm in diameter, placed at the edges of the two solar cell panels of the “NOZOMI” spacecraft. Electron temperatures can be measured in plasmas with densities exceeding 1000 cm^-3 with sufficient accuracy. The maximum sampling rate of 8 data points per satellite spin for each probe allows high resolution measurements (i.e., an angular resolution around the spin axis of 23 degrees). Additionally, the probe can measure the anisotropy of the electron temperature, if it exists. It is also possible to infer the existence of nonthermal electrons.

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A large earthquake (Ms 7.1) occurred off northwest coast of Papua New Guinea (PNG), and a massive tsunami attacked villages to cause a devastating damage. In an attempt to ascertain the tsunami source, we investigate the source rupture process using teleseismic data at IRIS network as well as local data at Jayapura, Irian Jaya, station. The source parameters obtained are: (strike, dip, slip) = (301°, 86°, 91°); the seismic moment = 4.3 × 10¹⁹ Nm (Mw = 7.0); the duration of main rupture = 19 s; the centroid depth = 20 ± 5 km; the extent of rupture along the fault strike = 40 km; the average dislocation = 1.8 m; the stress drop = 7.3 MPa. The tsunami magnitude Mt determined from tide-gage data at long distance is 7.5, significantly larger than Ms, so that the PNG earthquake is characterized as a tsunami earthquake. Tsunami earthquakes might have been caused by slow rupture, submarine landslide, and high-angle dip-slip. Our teleseisimic analysis precludes the first two candidates and favors the third one as a source of the present earthquake, although it does not necessarily exclude the possibility of an aseismic landslide induced by the main shock or its aftershocks.

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A total of 115 ceramic specimens out of 41 samples from 9 archeological sites in Giza, Fayoum, Benisuef, El Minia, Malawy, and Sohag were collected. They represent 14 well-determined ages covering the last 6000 years. Rock magnetic properties such as Curie temperature and hysteresis loops have been measured for these samples to identify the magnetic carrier; it is found to be fine-grained magnetite. All specimens were investigated using the classic Thellier double heating technique (Thellier and Thellier, 1959) and the modification after Odah et al. (1995) to obtain the paleointensity data. These paleointensities and the previous results of Odah et al. (1995) were used to improve the secular variation curve of the geomagnetic field in Egypt for the last 6000 years. This curve shows a maximum of 72.8 μT at about 250 AD and a minimum of 33 μT at about 3500 BC. It also shows a general decrease of the magnetic moment during the last 2000 years.

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