We study numerically the interaction of cold ionospheric ions in the tail lobe with a plasmoid propagating steadily in the tailward direction. We have found that significant energization of cold ions occurs at the encounter with a plasmoid, where three types of the interaction processes are taking place: First, ions show gradient and curvature drift motions as the plasmoid approaches. These ions are accelerated up to ∼1 keV by the cross-tail electric field accompanying with the plasmoid motion (type-I energization). Second, some of the ions get large pitch angles after the type-I acceleration, and then mirror reflected by the plasmoid. These ions are accelerated up to 10 keV after the reflection (type-II energization). Third, the motions of the ions near the plasmoid become highly non-adiabatic, because their gyroradii become comparable to the field-line curvature radius after the type-I energization. Consequently the energy distribution of these ions is broadened in the trailing side of the plasmoid (type-III energization). These theoretical results are successfully compared with the recent GEOTAIL observation showing the dynamic interaction of cold ions with a plasmoid and their subsequent energization.

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The physical mechanisms that might determine the damping rates and resonance widths of Pc3-5 pulsations are considered. To estimate the role of ionospheric dissipation, a numerical model, based on a calculation of the complex eigenfrequencies of Alfvén field line oscillations within the approximation of a “thin” ionosphere and for a realistic ionosphere has been used. At middle latitudes the Joule dissipation in the ionosphere may account for the experimentally determined width of the resonance peak of the fundamental Alfvén mode. The meridional spatial structure of higher harmonics is determined by nondissipative mechanisms. The calculations predict a rapid decrease of the Q factor of the magnetospheric Alfvén resonator at L < 1.5. The effect is related to the violation of the thin ionosphere approximation at low latitudes. Experimental support for the calculations was found while analyzing the meridional distribution of the damping rates of P_sc3 pulsations observed along the 210° magnetic meridian network.

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Simultaneous occurrence of Pc5 geomagnetic pulsations is studied using high time resolution geomagnetic data (sampled every 10 see) from the Scandinavian IMS Magnetometer Array and the North American IMS Magnetometer Network. Although the pulsation activity is longitudinally localized in most cases, an event with exceptionally coherent and similar wave form on both dawn and dusk sides was observed from 1500 to 1600 UT, on Sep. 27, 1978. The coherent oscillation was also observed at low latitude stations. We analyze this event further in detail by adding data from the ISEE-3 satellite in the interplanetary space, and from the geostationary satellites, GOES-2 and -3. These data show that this event occurred under such a peculiar solar wind condition as stable northward, anti-Parker IMF direction, and high solar wind speed (∼620 km/sec). The correspondence between the variation on the ground and that of dynamic pressure of the solar wind is found. The most likely source of this event is the magnetospheric cavity resonance generated by increases of the dynamic pressure of the solar wind.

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The equations of ionospheric electrodynamics are developed for a geomagnetic field of general configuration, with specific application to coordinate systems based on Magnetic Apex Coordinates. Two related coordinate systems are proposed: Modified Apex Coordinates, appropriate for calculations involving electric fields and magnetic-field-aligned currents; and Quasi-Dipole Coordinates, appropriate for calculations involving height-integrated ionospheric currents. Distortions of the geomagnetic field from a dipole cause modifications to the equations of electrodynamics, with distortion factors exceeding 50% at some geographical locations. Under the assumption of equipotential geomagnetic-field lines, it is shown how the field-line-integrated electrodynamic equations can be expressed in two dimensions in magnetic latitude and longitude, and how the height-integrated and field-aligned current densities can be calculated. Expressions are derived for the simplified calculation of magnetic perturbations above and below the ionosphere associated with the three-dimensional current system. It is shown how the base vectors for the Modified Apex coordinate system can be applied to map electric fields, plasma-drift velocities, magnetic perturbations, and Poynting fluxes along the geomagnetic field to other altitudes, automatically taking into account changes in magnitude and direction of these vector quantities along the field line. Similarly, it is shown how Quasi-Dipole coordinates are useful for expressing horizontal ionospheric currents, equivalent currents, and ground-level magnetic perturbations. A computer code is made available for efficient calculation of the various coordinates, base vectors, and related quantities described in this article.

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A new-type source of power line harmonic radiation (PLHR) is described in this paper to point out its significance to the magnetospheric emissions. Characteristic electromagnetic fields were observed over the Kola Peninsula, northern Russia, during the flight of the balloon B₁₅-2N in 1982. The source is characterized by (a) the fundamental frequency of 24.4 Hz, (b) the harmonic spectrum continuously extending up to VLF, and (c) the isolation from commercial power lines. These characteristics are different from the previously reported PLHR sources that could trigger the magnetospheric emissions. Based on the low impedance field and the amplitude variation along the balloon trajectory, the source can be modeled by a horizontal electric dipole or a horizontal magnetic dipole, and then the source distance is estimated within the induction area of a few hundred kilometers. The most probable source is an electric railroad or a single-phase power line, driven by an isolated power generator, and located on the Kola Peninsula. Estimating the radiation power through the ionosphere, it is shown that enough power to trigger magnetospheric emissions may be radiated into the magnetosphere from the source. Therefore, it is suggested that the source can be recognized as a new-type PLHR source possibly related to magnetospheric emissions.

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We have attempted a blimp-borne magnetic survey over the Unzen Volcano which has been erupting since November, 1990. The first attempt, made in January, 1992, was unsuccessful, but the second one in March, 1992 was partly successful, yielding the distribution of the geomagnetic total intensity at an altitude of about 1, 500 m. These total intensity data could be interpreted in terms of inhomogeneous magnetizations of rocks forming respective mountains of the Unzen Volcano. The east of Mt. Fugen, which is the site of current lava extrusion, shows a magnetization of 2∼3 A/m. This result would be an important piece of information for a study of volcanomagnetic effect, in particular in constructing a thermal demagnetization model.

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