In the field of nonlinear waves, there exist two kinds of waves, i. e., one is Non-Coupled Simple Wave (nonlinear P wave) and Coupled SimpleWave (nonlinear S wave). In this paper, the problem is limitted to the two-dimensional case. After numerical computations, we have then found that the behavior of waves in the nonlinear wave field is governed by the theory of Simple Waves. Even complex wave form can be analyzed as composite Simple Waves.

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Nighttime hourly mean values of D, H and Z (or X, Y and Z in a fewcases) from 113 observatories for the interval 1964.0 to 1966.0 have been analyzed to determine the semi-annual variation. Results from the 84 observatories with dip latitudes between ±60°have been subjected to spherical harmonic analysis to determine the coefficients of the internal and external parts. Only those coefficients that are found to be significantly different from zero at the 5 per cent level have been included. One of the main objectives is to obtain a reliable estimate, with confidence limits, of the internal/external ratio at a very low frequency for constraining estimates of the deep conductivity of the mantle. It is shown that a model that includes only the principal P01 term can lead to a seriously misleading internal/external ratio.

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We performed high resolution magnetic measurements on about 180 m of continuous U-channel samples from Sites 1012 (East Cortez Basin) and 1013 (San Nicolas Basin) that were recovered during Ocean Drilling Program Leg 167 to the California Margin. Measurements were made at 1-2 cm intervals from near-complete composite stratigraphic sequences at both of the studied sites with the goal of obtaining high spatial resolution of sediment magnetic properties, including detailed characterization of variations in magnetic mineralogy, concentration, and grain size. The decay of a metastable magnetic mineral or the dissolution of fine-grained magnetite by organic matter reduction had strongly affected both cores, reducing the magnetic intensity to 7%-10% of the initial magnetization. Measurements were carried out ca. 4-6 months after the cores were drilled. Despite the reduced magnetic signal we were able to define a stable characteristic remanence for most of the core. Cyclic variations that were observed over short and long stratigraphic intervals are strongly driven at Earth orbital periodicities and have been used to obtain a detailed age model based on comparison with the insolation record.

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Paleomagnetic results are obtained from 41 sites from the Chopyeong Formation within the Eumsung basin, located along the northern boundary of the Ogcheon Belt, Korea. The Chopyeong Formation, deposited in early Cretaceous, yields the mean direction of D/I = 347.8°/57.3° (k = 92.8, α95 = 2.5°) before tilt correction, and D/I = 0.7°/61.7° (k = 19.6, α95 = 5.5°) after tilt correction. The parameter estimating fold test and the stepwise unfolding test of the red bed and greenish mudstone of the Chopyeong Formation yield the maximum value of k at 21.9% and at 20% untilting, respectively, indicating that the remanence whose mean direction of D/I = 350.8°/57.9° (k = 177.9, α95 = 1.8°) at 20% untilting was acquired during or after tilting of the strata. The comparison of the paleomagnetic pole from the Chopyeong Formation with those from the Youngdong basin and the Euiseong area in the Gyeongsang basin indicates that the remanence was acquired during late Cretaceous to early Tertiary. Electron microscope observations and rock magnetic experiments show that secondary hematite and magnetite grains of single domain to pseudo-single domain size were authigenically formed under the influence of fluids presumably triggered by the igneous activities, thus confirm the chemical remagnetization. It is revealed that the age of the granite in the east is Jurassic because the mean direction of the east granite (D/I = 347.0°/47.7°, k = 40.2, α95 = 3.6° ) is similar to the Jurassic direction of Korea Peninsula. The age of the granite in the west, however, is left undetermined whether it is Cretaceous or Jurassic because of the weak intensity and instability of the remanence of the granite during demagnetization treatments.

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The ELF- and the ULF-MT surveys were carried out in the northern part of Miyagi Prefecture, northeastern Japan. This area is one of the most seismically active areas in this region, where hypocenters of microearthquakes are distributed on a fault plane at depths from 2 to 16 km. The aim of the present study is to investigate the relationship between electrical resistivity structure and the hypocentral distribution of microearthquakes in the area. The calculated impedance tensor at each site has been obtained from the observed data and decomposed to remove galvanic distortion, provided that the regional strike is N32. E to obtain the 2-D apparent resistivity and phase responses. The resistivity structure obtained by the inversion process using smoothness constraint shows that the relatively electrically conductive layer at depths from 4 to 10 kmcorresponds to the zone where the microearthquakes occur. The fact that the conductive zone correlates with the hypocentral zone is probably attributed to fluids in the crust. Another more conductive block is found at depths from 1 to 3.5 km and the bottom boundary of this conductor appears to restrict the uppermost depth where the microearthquakes occur. This subsurface conductor is interpreted as a marine sediment deposited during the Tertiary period. In the lower crust, the relatively conductive blocks (lower than 5Ω·m) exist below a depth of 15 km.

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It is well established that geomagnetic activity in the declining phase of a solar cycle is a useful precursor of the amplitude of the solar activity in the next cycle. In the present analysis, we show that the frequency of occurrence of Kp index with values (0-1) representing geomagnetic calm and with values between 4 and 7 representing moderate geomagnetic disturbances in the declining phase of a solar cycle is linearly related to the sunspot maximum of the next cycle. Highest correlations are obtained when the frequencies are averaged over three years preceding the solar minimum epochs. We also show that the frequency of occurrence of consecutive 4 or 6 intervals of Kp with the same magnitude (0-1 or 4-5) is also equally reliable as a predictor of the ensuing solar maximum. The rate of increase of sunspot number to the solar maximum and its subsequent rate of decline to the next minimum can also be predicted reliably with these frequencies. Based on the observations for 1993-1996, we expect the coming solar maximum to be associated with an annual mean sunspot number of about 140, with a rate of ascent of 35/year and a decline rate of about 25/year.

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The local time and longitudinal variations of the amplitude of the equatorial electrojet (EE) are investigated using the POGO series satellite data. An iterative normalization scheme is developed to separate the variations of the amplitude of the EE with respect to longitude and local time. The resulting local time variation of the EE compares favorably with observatory based studies; however, the longitudinal variation is not well resolved. The altitude of the satellite is another factor that affects the amplitude of the EE. We use a simple linear scaling of amplitude of the EE with the inverse of the satellite altitude. An experiment including only the satellite passes below 450 km altitude indicates that there may be problems in correcting the data from higher altitudes. The reason behind the discrepancy between the results from the data limited to below 450 km and the full data set is not understood and requires further investigation.

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The interaction between the magnetized plasma flow and an obstacle was investigated in the computer simulations described here by using a three-dimensional hybrid code (kinetic ions and massless fluid electrons). The results, which are relevant to the interaction between the solar wind and an unmagnetized planet (Venus or Mars), show that fundamental structures (bow shock and magnetotail) are formed. When a reflecting boundary is used at the obstacle, the magnetic field configuration was clearly asymmetrical in the direction of the convection electric field. This asymmetry is a result of differences in ion acceleration due to the convection electric field. Asymmetry is also evident when the size of the obstacle is close to the Larmor radius of protons. The shock of a smaller obstacle is weaker than that of a larger obstacle, but the shock size is almost independent of the obstacle size.

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