The characteristics of the wave exit area on the lower boundary of the ionosphere is inferred from the distribution of the magnetic intensities of the VLF waves simultaneously received at six observation stations near the Siple conjugate point at Roberval in Canada on July 23, 1979. In order to estimate the characteristics of the wave exit area, we have to make some assumptions about the conditions of the input wave injected to it and the propagation mechanism in free space. Applying the principle of Huygence for electromagnetic wave in free space to the wave radiated from the exit area, we compute the distributions of the wave magnetic intensity on the ground. By a least square technique, we infer the location and shape of the exit area making the wave intensity distribution observed on the ground. The obtained results are as follows. It was found that three wave exit areas at least existed over the observation station network. It was confirmed that the signals radiated from the Siple transmitter (Siple waves) were propagated along the ducts in the magnetosphere. The wave exit areas were generally elongated in the east-west direction, suggesting that the shapes of the ducts are also elongated in the east-west direction.

View full abstract

The thermospheric nitric oxide density at solar minimum was measured by means of the gamma band day airglow with a rocket-borne photometer launched from Uchinoura (31°N) on January 15, 1987. The peak density was about 1.4×10⁷cm^-3 at an altitude of 105-110km, and the density decreased with altitude as an exponential function. This result is consistent with observations made at the last solar minimum, and allows us to construct an observational model for the variation in thermospheric nitric oxide profiles throughout a solar cycle at a low latitude.

View full abstract

A computer experiment is carried out to study the dynamic behavior of plasma particles in response to self-consistent electromagnetic and electrostatic fields produced by an artificial injection of a dense electron beam into the ambient plasma. A two-and-one-half dimensional electromagnetic particle code (KEMPO) is used for this purpose. The electron beam is assumed to be injected along the external magnetic field, B₀, and to have a spatially finite extent in directions both parallel and perpendicular to the beam motion at t=0. Most of the beam electrons are decelerated, and this deceleration is accompanied by an elongation and splitting of the beam. However, a fraction of the electrons in the beam is not decelerated but instead is accelerated in both positive and negative directions along B₀. A substantial heating of beam electrons is also observed. Associated with the acceleration and thermalization of the beam electrons, various kinds of electromagnetic and electrostatic waves are excited through wave-particle interactions. On a time scale of ion motion, ions are attracted toward the center of the moving beam, forming an ion density peak, which, in turn, causes a strong acceleration of electrons. A BGK type quasi-steady state is reached and maintained for a finite time.

View full abstract

Theoretical studies concerning MHD source waves of long-period (T=10-600s) magnetic pulsations are reviewed. The source waves can be classified into two groups: One is external origins, that are upstream waves driven by the ion beam instabilities in the earth's foreshock, surface waves excited by the Kelvin-Helmholtz instabilities in the magnetospheric boundary, and sudden impulses caused by an interplanetary shock and dayside reconnection. The other is internal origins, e. g., drift mirror instabilities in ring current hot ions and sudden changes during substorm onset in the nightside magnetosphere. The upstream waves, the surface waves, and the drift waves associated with a finite energy distribution and a finite thickness of layered plasma show a narrow-band frequency, while the sudden impulses have a broad-band frequency. These source waves with a nearly monochromatic frequency and a broadband frequency can couple into standing field-line oscillations in the inner magnetosphere through the field-line resonance mechanism.

View full abstract

The stratospheric aerosol and ozone were observed by using solar occultation technique on board the satellite “Ohzora” during about 3 years from March 1984. The instrument is a two-channel sun-photometer at the wavelengths of 600 and 1000nm. As the detector for each channel a two-dimensional CCD image sensor was used to obtain vertical resolution of the order of 1km. In this paper the general description of methods of observation and analysis, and examples of the initial results are presented.

View full abstract

The infrared atmospheric band airglow radiometer (IRA) was flown aboard the satellite OHZORA to measure the mesospheric ozone profile by using the O₂ 1.277μm emission from the atmospheric limb. The IRA also measures the CO₂ 15μm radiation with the thermistor bolometers to get information on the satellite attitude and the tangential heights of the line of sight of the sensors. Some radiance profiles of the limb at two wavelengths were obtained in February and March 1984, when the thermistor data confirmed the satellite was being kept without a spinning motion. The dedueced mesospheric ozone profiles are compared with Krueger and Minzner mid-latitude ozone model and the SME satellite data. A difference between the profile around a latitude of 60°S and that around 50°S exists above about 75km height, and the latter profile seems to be similar to the mid-latitude one. The density in the heights 75-95km around 60°S shows an almost constant value of about 5×10⁷cm^-3.

View full abstract

Several current channelling models between two oceans are presented for studying the frequency responses of the transfer functions and the anomalous horizontal magnetic field in the ‘E-polarization’ case (i. e., the inducing magnetic field is perpendicular to the direction of the channel). The results obtained from this numerical investigation give support to the idea that at longer periods, the lack of frequency dependence of the transfer functions and the anomalous horizontal magnetic field is the characteristic consequence of the channelling effect of the oceanic induced currents. On the contrary, the corresponding 2-D local induction models show that the frequency responses of the transfer functions and the anomalous horizontal field are quite sensitive to the period of the inducing field at the longer periods. When there is no highly conducting layer lying under the surface structure, we have found another property which arises from the channelling effect of the oceanic induced currents; that is, the vertical magnetic component is nearly in-phase with the normal magnetic field. Likewise, the horizontal component of the anomalous magnetic field will also be nearly in-phase with the normal field. However, when a conducting layer exists below the ocean and its buried depth is not very deep, the in-phase properties stated above no longer hold. Furthermore, we investigate the behaviour of the oceanic current in a channelling model for the ‘B-polarization’ case (i. e., the inducing magnetic field is parallel to the channel) at one period, T=10000s. The result also shows that the anomalous magnetic field is nearly in-phase with the normal magnetic field, provided that no highly conducting layer lies under the surface structure.

View full abstract

This paper reviews the topical conference named above, which was held in Kyoto, March 9-13, 1987. With a well organized program of excellent papers, the symposium celebrated a right of passage in the life of our discipline. After growing in stages from a largely qualitative discipline divided into distinct, mostly non-communicating compartments, the field enters the fourth decade of the space age a largely quantitative, communicating, integrated discipline. The aspect most indicating achieved maturity is the shared view that the solar wind-magnetosphere-ionosphere system is an interactively coupled unit, which might be called the geospace system, whose properties must be determine through discipline-wide cooperative research. In the area of theory, the geospace system's great complexity and the drive to understand it quantitatively put great emphasis on solving the global coupling, dynamics and mapping problems and building numerical models of increasing comprehensiveness and predictive power. In the area of observations, the corresponding emphasis is on coordinated campaigns and computerized data management, analyses and displays. Acknowledging the historical imperative of the time, the symposium assembled top people to relate progress toward quantitative empirical and theoretical understanding of all areas of the geospace system. The resulting global view of the state of our science shows great strength throughout, with areas of rapid progress and areas of difficult progress, but motion on all fronts. Under the pull of a common goal to achieve a fully predictive science of the geospace environment, we see the separate motions converging.

View full abstract