An average shear-wave velocity structure has been estimated for the path between the Kamchatka Isthmus and Petropavlovsk-Kamchatski. It is obtained from the Monte Carlo inversion of the Rayleigh and Love wave group velocity dispersion curves measured using broad-band seismograms of events in Northern Kamchatka recorded by the IRIS station PET in Petropavlovsk-Kamchatski. The Moho interface was found at a depth of 35±5 km and the Konrad one at 18±4 km. An important feature of the found structure is a lowvelocity in the upper mantle. This result is coherent with the recent and present-day volcanic activity in Kamchatka. Synthetic long period seismograms computed for the obtained structure are in good agreement with observed ones.

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The coupled seismic to gravitational surface wave fields are analyzed in a liquid layer lying on the gravitating elastic, low-rigidity half-space. Solution is obtained within the framework of the normal mode formalism applied to the flat ocean-solid Earth model. From the theory of propagation of coupled surface waves (Rayleigh and Love) in layered media, we find the individual multipliers that determine the surface wave spectrum over the entire frequency range. Spectra of excitation functions are investigated for dip-slip point source in the half-space. Main results can be summarized as follows. When the half-space is filled with sediments, dip-slip excitation functions of gravity and Rayleigh waves are one order of magnitude larger than for the half-space composed of hard rocks. Including gravity in the elastic medium essentially changes the character of gravity wave spectrum, leading to an appearance of the third maximum. At the deepening of the source amplitude of this maximum increases. Theoretical marigrams show that including gravity in the half-space also increases period of the gravity wave excited by deep sources by a factor of two, up to 10 minutes. At the same time, presence of gravity force in the half-space has no effect on the spectrum of the Rayleigh wave.

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Estimates of the C-response function were determined by Z : H method to obtain conductivity and depth values for a substitute perfect conductor (conductosphere) beneath the Indian region, utilizing geomagnetic variations at periods of 27-day and its harmonics. Two and half years of continuous geomagnetic data were utilized. These data were recorded during 1975-77, at a chain of 13 stations confined to the 150⁰ geomagnetic longitude band, which extended from the dip-equator at the southern tip of India, to the northern parts of Russia. Complex demodulation techniquewas employed to determine the electromagnetic (EM) responses. Taking advantage of the dense latitudinal distribution of the observatories, the demodulates of all the stations were tested statistically to check the validity of the P₁⁰ approximation for the inducing field. Single-station response estimates, for a 27-day period, computed by a robust method have shown that reliable EM responses (consistent with P₁⁰ source dependence and with local 1-D Earth structure) could be obtained for only 6 stations, all situated in the mid-latitude region. The depth estimates at all 6 stations are consistent, including Sabhawala (SAB) which is situated close to the Himalayan collision zone. The negligible differences in the depth estimates of these mid-latitude stations do not show any latitudinal dependence, as against such an observation reported for the European and the North American regions. The mean depth of the conductosphere is found to be 1200 (±200) km, with an average conductivity of 0.7 (±0.3) S/m. Comparison of the mean geo-electrical structure with those of other regional models shows that the presence of a mid-mantle conductor at 850 km depth could be considered to be a global phenomenon.

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A balloon-borne resonance fluorescence instrument for in-situ measurement of atomic oxygen (O(³P)) was developed and its performance was characterized based upon numerical simulations and laboratory tests. A simultaneous measurement of O(³P) and ozone (O₃) in the upper stratosphere was carried out onboard a high altitude balloon launched from Sanriku (39°N, 142°E), Japan on 9 September 1997. O3 was measured on the same balloon by the solar UV absorption technique. The measured density ratios [O(³P)]/[O₃] at altitudes 38-44 km were found to be consistent with the calculated within the experimental uncertainties, although a systematic discrepancy was found above 41 km. It was difficult to make a detailed discussion about this discrepancy due to the insufficient precision and accuracy.

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The behavior of toroidal mode oscillations of standing Alfven waves (refer to as standing Alfven oscillations) in the coupled magnetosphere-ionosphere system is investigated using a trapezoid-shape magnetosphere model. It is found that the magnetic perturbation is transmitted across the ionosphere differently in the two cases where the ionospheric electric field perturbation is static (Pedersen conductivity > Hall conductivity) and where it is inductive (Pedersen conductivity < Hall conductivity). It is noted that the ionospheric Hall current for the inductive condition shields the magnetic field perturbation. The north-south asymmetry of the conjugate ground magnetic perturbations is calculated by using a trapezoid model with the ionospheric and magnetospheric parameters based on the IGRF and IRI. It is revealed that the ionospheric electric field is almost static for the fundamental mode oscillation, whereas inductive for the higher harmonic ones. It is also found that the north-south asymmetry of the ground magnetic perturbations depends not only on the L-value but also on magnetic longitude; this is because the ionosphere and magnetic field conditions are not uniform as a function of longitude.

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Pi 2 pulsations at low latitudes are examined with magnetic fields data at the 210° magnetic meridian (MM) stations in 1991. Due to high degree of coherence over most latitudes, 68 low-latitude Pi 2 events at the 210° MM stations are identified with reference to same waveforms on the magnetogram at Lunping (189.5° MM, L = 1.06). With spectral power analysis, the ratio of the first four harmonic frequencies of low-latitude Pi 2 pulsations is about 1 : (1.7 ± 0.1) : (2.3 ± 0.1) : (2.9 ± 0.1). By using a box model for the inner magnetosphere, the cold linearized MHD wave equations are studied with realistic Alfven speed profile for nonuniform ambient magnetic fields. With appropriate parameters to depict the magnetospheric environments during the aforementioned period, numerical results are acquired with the fourth order Runge-Kutta method. It is found that the ratio of the first four harmonic frequencies of plasmaspheric cavity resonances is about 1 : 1.7 : 2.4 : 3.1 that is consistent with data analysis. This suggests that low-latitude Pi 2 pulsations at the 210° MM stations may be plasmaspheric cavity resonances driven by fast compressional waves owing to the impulsive source at the magnetotail.

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The Lunar Radar Sounder (LRS) experiment on-board the SELENE (SELenological and ENngineering Explorer) spacecraft has been planned for observation of the subsurface structure of the Moon, using HF radar operating in the frequency range around 5 MHz. The fundamental technique of the instrumentation of LRS is based on the plasma waves and sounder experiments which have been established through the observations of the earth's magnetosphere, plasmasphere and ionosphere by using EXOS-B (Jikiken), EXOS-C (Ohzora) and EXOS-D (Akebono) satellites; and the plasma sounder for observations of the Martian ionosphere as well as surface land shape are installed on the Planet-B (Nozomi) spacecraft which will arrive at Mars in 2003. For the exploration of lunar subsurface structures applying the developed sounder technique, discrimination of weak subsurface echo signals from intense surface echoes is important; to solve this problem, a frequency modulation technique applied to the sounder RF pulse has been introduced to improve the resolution of range measurements. By using digital signal processing techniques for the generation of the sounder RF waveform and on-board data analyses, it becomes possible to improve the S/N ratio and resolution for the subsurface sounding of the Moon. The instrumental and theoretical studies for developing the LRS system for subsurface sounding of the Moon have shown that the LRS observations on-board the SELENE spacecraft will give detailed information about the subsurface structures within a depth of 5 km from the lunar surface, with a range resolution of less than 75 m for a region with a horizontal scale of several tens of km. This capability is evaluated to be sufficient for study of the thermal history of the lunar surface region relating to a time scale of several tens of millions of years.

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The EISCAT Svalbard Radar (ESR) has been used to obtain ion velocities in the lower thermosphere. By using beam swinging and assuming homogeneity and stationarity of the plasma, first approximations to the electric field have been deduced, and thus the thermospheric neutral wind has been estimated. From these derived parameters, we have estimated the gradient Richardson Number. Although many assumptions must be made, there is an indication that electrodynamics is able to contribute to enhancement or even production of neutral-air turbulence in the lower thermosphere. Finally, we outline a proposal for an analogy to the Reynolds Number, but reflecting the relative importance's of the contribution of ion-drag to the neutral dynamics and the kinematic viscosity.

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The geometric albedo of the Moon at the wavelength of hydrogen Lyman α (HLyα 121.6 nm) was derived from an imaging observation by the ultraviolet imaging spectrometer (UVS) during the lunar encounter of the NOZOMI spacecraft. The solar HLyα irradiance data measured by the UARS/SOLSTICE at the time of UVS observation were adopted. We obtained an average geometric albedo of 5.2 ± 0.9% for the sunlit region where the UVS observed. Our result agrees with the geometric albedos obtained from the observations by Apollo 17 and Astro-2/HUT, though the observation geometry and area are completely different from each other. There exists a significant difference of the albedos from place to place in the observed lunar surface ranging from 2.3 ± 1.1% to 6.0 ± 1.0%. It is noted that the observed contrast at the FUV wavelength is positive to that seen in the visible region.

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