The whistler mode wave-particle interaction in a homogeneous magnetic field is studied by computer simulation. A monochromatic whistler wave packet propagating parallel to the magnetic field is assumed to interact with counter streaming high energy electrons. Main emphasis is laid on the following points: (1) whether or not the emission is triggerable within the homogeneous model, (2) if so, how much the frequency deviate from the triggering frequency and (3) what is the physical mechanism of the frequency deviation. It is demonstrated that the new emission is triggered owing to detrapping of phase-bunched electrons from the pulse. The emission shows a relatively small rising tone followed by subsequent frequency oscillations. The range of the frequency variation is about 5% of the triggering pulse. This is supposed to correspond to the “embryo” emission phase or to the initial phase of triggering of emissions.

View full abstract

Being based on the existence of the disc plasma flowing outward in the localized flow region with the super magnetosonic velocity called Jovian disc wind, a dynamical feature of the Jovian magnetosphere has been studied in the equatorial plane. Using a concept that the pressures inside and outside of the magnetopause are balanced by each other, a pressure balance equation has been obtained and calculated numerically to express the shape of the Jovian magnetosphere. The main pressure supporting the solar wind pressure is not the planetary magnetic pressure but the dynamic pressure of the Jovian disc wind. The nature of the Jovian disc wind with large azimuthal component in its bulk flow, therefore, has a great influence on the shape of the Jovian magnetosphere. The results of our numerical calculation of the pressure balance equation indicate a clear dawn-dusk asymmetry of the Jovian magnetosphere; i. e., Jupiter has a large scale magnetosphere in the dawn side and has a relatively small scale magnetosphere in the dusk side. Our calculation also indicates a sensitive response of the location of the Jovian magnetopause for the variation of the solar wind pressure. This feature coincides with the in-situ observations by Pioneer 10, 11, Voyager 1 and 2, and is called the “spongy nature” of the Jovian magnetosphere. In addition to the calculation for the super magnetosonic wind solution, we have obtained the shape of the magnetosphere for the case of sub-magnetosonic breeze. The results for the breeze case indicate that the stable magnetopause is able to exist only in the limited region in the day side.

View full abstract

Large-scale structures of the solar wind plasma during the severe geomagnetic storm of August 27-29, 1978 are studied on the basis of IPS and spacecraft observations. Three-dimensional configuration of an interplanetary disturbance which caused the SSC of August 27, 1978 was an oblate sphere having an axial ratio of 1.7. Approximate excess mass and kinetic energy contained within the high-speed portion of the disturbance (-500km s^-1) were. 10¹⁶g and 3×10³¹erg, respectively. An interplanetary disturbance was also observed on August 28, 1978 during the main phase of the geomagnetic storm. It is suggested that the solar-filament activity which took place near the solar disk center in August 23-25, 1978 caused these interplanetary disturbances.

View full abstract

An enhancement of plasma density observed during a neutral gas injection in Space Experiments with Particle Accelerators: SEPAC by the Space Shuttle/Spacelab-1 is presented. When a plume of nitrogen gas was injected from the orbiter into space, a large amount of plasma was detected by an onboard plasma probe. The observed density often increased beyond the background plasma density and was strongly dependent on the attitude of the orbiter with respect to the velocity vector. This effect has been explained by a collisional interaction between the injected gas molecules and the ionospheric ions relatively drifting at the orbital speed.

View full abstract

We report paleomagnetic results from 45 oriented samples collected at 8 sites from the fossiliferous marine Pontgravé Formation (3 sites) and continental Bécancour Formation (5 sites) of the gently dipping Late Ordovician Richmond Group sediments in the St. Lawrence Lowlands of Quebec. Stepwise thermal and alternating field demagnetization studies revealed the presence of two groups of coherent magnetization (components: A and B) before and after tilt correction. The group A magnetization is characterized by a stable direction (D=175°, I=-22°, α₉₅=8.2°) with unblocking temperatures (T_UB) between 500° and 630°C and coercitivities (H_C) generally larger than 100mT; this direction is a secondary chemical remanence probably acquired during the uplift related to the Acadian orogeny (Middle to Late Devonian). Component B (D=184°, I=20°, α₉₅=9.1) is characterized by H_C spectra of 10 to 30mT and T_UBs in the range: 300-540°C. This component is interpreted as the oldest and it is possibly primary. The paleopoles of components A and B are 116°E, 55°N (d_p=59°, d_m=10.8°) and 105°E, 33°N (d_p=5°, d_m=9.5°), respectively. This last pole position could characterize the Late Ordovician depositional event. A comparison of this pole with paleomagnetic data of the same age from cratonic North America suggests a small apparent polar motion from Early to Late Ordovician. Pole of the same age obtained from the northern Appalachians are significantly different. A 50° clockwise rotation of the mountain chain is a possible solution to the problem if component B is not an overprint. However, deformation of the Appalachians characterized by a mosaic of small blocks or else magnetic overprinting still remain the two better alternatives.

View full abstract