Hiroshi Fukunishi

Relationships of the characteristics of magnetohydrodynamic waves to plasma density gradients near L = 4

Abstract Important recent work, both experimental and observational, has provided exciting new results and understandings of the excitation and localization characteristics of magnetohydrodynamic waves (ω ⪡ ion gyrofrequency) that exist in the Earths magnetosphere. This paper reviews several of our recent contributions to this research area, with special emphasis on the importance of magnetospheric plasma density gradients in determining wave localizations. The observational results are discussed in the context of current theoretical ideas of hydromagnetic wave excitation in the Earths space environment.

Conjugacy of ELF-VLF emissions near L = 6

Abstract Conjugate observations of ELF-VLF emissions, magnetic pulsations and aurorae were carried out at Syowa Station in Antartica and Husafell in Iceland from 29 July, 1977 to 18 September, 1977. Husafell is located at a distance of about 50 km from the point of Syowa. The conjugacy of ELF-VLF emissions depends on their type, whether polar chorus, quasi-periodic emissions, bursts of discrete emissions or auroral hiss. Polar chorus and quasi-periodic emissions are observed simultaneously at the conjugate-pair stations. This suggests that the emissions are generated near the equatorial region in the outer magnetosphere and propagate to both hemispheres along the field lines. The conjugacy of bursts of discrete emissions and auroral hiss is generally low. The interrsity of auroral hiss is much stronger at Syowa (winter hemisphere) than at Husafell (summer hemisphere); just the opposite terrdency is observed for bursts of discrete emissions. The low conjugacy of these emissions may be due to differences in the geophysical parameters, such as the magnetic field, magnetic dip angle and the plasma density in the two conjugate ionospheres. Preferential precipitation in the southern hemisphere explains the strong discrete emissions in the northern hemisphere. The growth rate of auroral hiss is large in the low plasma density (winter hemisphere) ionosphere.