Co-seismic horizontal displacements, which have been obtained from recently released GPS observations on the Akashi Kaikyo Bridge, are examined for their consistency with displacements observed in the vicinity of the bridge. An E18.7°S displacement of 25.0 cm should be removed from them. The adjusted data indicate an additional fault segment beneath Akashi Strait. We construct a new fault model by adding this segment to a model assumed previously. We then recover the slip distribution over the new model by inverting these data together with other geodetic observations. The displacements calculated from the recovered distribution fit the observations well, and the distribution of slip indicates that the additional segment is closely related to the southern main segment of the previous model. Joint inversion of the geodetic and waveform datasets suggests large slips with longer duration in the shallow parts of these segments.

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Fluid flowin the core is assumed to consist of a slowly varying (on time scales > magnetic diffusion time) part and a smaller, rapidly varying part as in the theory of the hydromagnetic dynamo put forward by Braginsky (1965). On the basis of this theory, geomagnetic secular variation models for the last 150 years are used to determine a rapidly varying, axisymmetric, poloidal motion of the fluid near the top of the core as a function of latitude in regions away from the equator. Approximations made in estimating this motion fail near the equator, thus restricting the estimates to latitudes ≥ 40°. Amplitude of the oscillating part of the axisymmetric poloidal flow is found to be ≤ 1 km/yr in the northern hemisphere, and nearly 3 km/yr in some parts of the southern hemisphere. The nature of temporal variation of this component differs significantly between the northern and southern hemispheres during the period under consideration.

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A short review is given of the contemporary concepts and controversies concerning the electromagnetic effects observed in space which are considered to be the results of energy transport from surface and/or lower atmosphere. A concept of a parametric amplifier in the stratosphere-mesosphere was recently suggested by the authors (1996) from the reanalysis of the experimental results from the AUREOL-3 satellite during active experiments MASSA with ground chemical explosions. Electric discharges in the stratosphere-mesosphere medium were suggested as a mechanism for this parametric amplifier. Such discharges, or localized electric current bursts in the Alfven wave frequency scale (-0.1-1 s^-1), could also play a role as a mechanism of effective energy transport from the surface to space layers. Among the possible EQ precursor effects, some can be related to local atmospheric electricity variations such as emanations of gas and/or aerosols, conductivity changes in the lower atmosphere, or non-linear combinations of acoustic waves with a meteor ionization channel. Thus a multidisciplinary search of EQ precursors, especially with regard to atmospheric electricity variations, lightning-type, or slower discharges related to meteor ionization, seems to be among the ways to deepen the understanding of the complicated relations between different layers of atmosphere and magnetosphere.

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The theory of equatorial electrojet predicts the presence of vertical ion currents (Pedersen currents) as a part of the electrojet current system. The vertical ion current density profile over the dip equator, that forms a part of the meridional current system is derived from an electrojet model. The joule heating due to these currents flowing upward during daytime for a local time for 1100 hrs has been estimated. The primary east-west current density of the model is kept at the same value as that measured by means of rocket-borne magnetometer on one occasion. The electrical power dissipated as heat in the narrow belt in the height region of 100-180 km is estimated and found to be significant. The height of maximum power dissipation coincides with the altitude of maximum ion velocity i.e. 122 km. By solving the heat conduction equation we obtain a maximum temperature increase of 8°K around 135 km. The importance of this localized heating in the lower thermosphere around ±2° of the dip equator is discussed.

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Recurrent geomagnetic disturbances are an important part of geomagnetic activities, which are associated with the neutral sheet structure in the heliosphere and the activities of long lived solar coronal holes. Another significant character is the periodic activities recorded by geomagnetic indices. In this paper an algorithm-Adaptive Filtering (AF), is introduced to forecast recurrent geomagnetic events based on the geomagnetic K index. Adaptive filtering can deal with nonstationary data and can adapt to changes in the data pattern. Therefore it is a very helpful method for forecasting the geomagnetic disturbances and the disturbances in the interplanetary space. By using AF technique a prediction for whole Bartels rotation can be obtained when output length is taken as 27-point. For recurrent periods the prediction efficiency is about 30%, the correlation coefficient is 0.55. For nonrecurrent periods the prediction efficiency and correlation coefficient decrease obviously, but the standard variance does not change very much.

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The micropulsation data (Pc3-Pc4 range) from off-equatorial and equatorial stations Alibag (ABG) and Tirunelvelli (TIR) in the Indian zone during 1991 are analysed for delineating the electrojet effect. The ratios of the spectral amplitudes at significant frequency bands the horizontal component of the magnetic field at TIR to that at ABG are worked out as a function of frequency. The results show that the lower frequencies undergo larger equatorial amplification. However, above a certain frequency the pulsation signal is found to attenuate rather than exhibit the general enhancement. The ratio becomes minimum around the period, 18 to 24 sec. At further higher frequencies, there is again the normal electrojet amplification. The explanation of such a behaviour of the electrojet on the pulsation amplitude is rather difficult at the present stage and to some extent becomes controversial even if it is offered.

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To study the ring current structure in the inner magnetosphere, we have statistically examined the magnetic field data acquired by ETS-VI (the Engineering Test Satellite-VI). During a magnetic storm, the Dst index shows a rapid recovery of its amplitude for about 9 hours on average after the main phase and a subsequent long-lasting slow recovery. We have investigated this “two-step recovery” of the Dst index by obtaining magnetic field vectors and calculating the current structure in the inner magnetosphere for each magnetic storm phase determined by the Dst index. From this study, following results are obtained: (1) Throughout the storm-time, disturbed magnetic fields exhibit clear day-night asymmetry with strong peak in the nightside. (2) During the main phase, southward perturbed field components have a relative bump in the nightside region between -2000 and -0400 MLT and between -4.0 and 6.4 R_E (geocentric distances in Earth radii). (3) The initial rapid recovery of the Dst index is considerably influenced by the nightside currents flowing between -1800 and -0600 MLT and between 5.6 and 7.2 R_E. These currents are thought to be mainly composed of the particles that escape the magnetosphere on the duskside flank, which are simulated in particle tracing in a realistic magnetosphere.

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Large number of high dispersion whistlers recorded at low latitude station Varanasi (L = 1.07) are analysed and it is find out that they have propagated along L ≈ 2.12-2.76. This is explained by considering the propagation of whistlers through the earth-ionosphere wave guide after exiting from the duct towards the equator. Using diffusive equilibrium model (DE-1), we have estimated equatorial electron density, total electron content in a flux tube and large scale convective electric fields which are in good agreement with the results reported by other workers from the analysis of mid latitude whistlers. The significance of this paper is to probe mid latitude plasmasphere using whistlers recorded at low latitudes. Further, an attempt has been made to study the propagation mechanism of low latitude whistlers.

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Recent three-dimensional simulations of the Martian plasma and magnetic field environment found some unique effects-a strong asymmetry of the bow shock and the magnetic field draping, asymmetry of plasma inflow to the wake, formation of secondary shocks near the boundary of the magnetospheric cavity. The predictions of the models are testified using the Phobos-2 data. It is shown, that, although, the models reproduce some features of the bow shock and plasma flow around the planet, the real picture appears to be more variable and complicated. We suppose that addition of planetary plasma originated from the atmosphere/exosphere and effects of mass-loading is necessary modification of three-dimensional models.

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The report of Nawa et al. (1998) that incessant excitation of the Earth's free oscillations was discovered in the low frequency spectra of the superconducting gravimeter at the Syowa station in Antarctica is reexamined. The mean spectra for Syowa are compared with those for Matsushiro, another superconducting gravimeter station in an extremely calm circumstance, hence showing a much lower noise level than Syowa. Although the spectra for Syowa have many peaks below 3 mHz corresponding to those present in the time-frequency diagram of Nawa et al., no similar peaks are found in the spectra for Matsushiro. This result suggests that the peaks below 3 mHz in the Syowa spectra are not real signals of the Earth's free oscillations.

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Imanishi (this issue) commented that (1) the noise level at Matsushiro, Japan (MA) is much lower than at Syowa Station, Antarctica (SY), (2) oscillation signals are not observed at MA, and therefore (3) peaks below 3 mHz observed at SY are unlikely to be real signals of free oscillations. We point out that (1) he made a comparison between MA in the Japanese quiet month and SY in the Antarctic windy month, (2) the Matsushiro record does show up oscillation signals, and therefore (3) his assertion that peaks below 3 mHz observed at SY are unlikely to be real signals is not founded.

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